Texas Instruments bq77908AEVM User manual

User's Guide
SLUU854–February 2012
bq77908AEVM Evaluation Module
The bq77908AEVM-001 evaluation module (EVM) is a complete evaluation system for the bq77908A, a
4-series to 8-series cell Li-Ion battery protection integrated circuit. The EVM consists of a bq77908A circuit
module and a resistor cell simulator module, which can be used for simple evaluation of the bq77908A
functions. The circuit module includes one bq77908A integrated circuit (IC), sense resistor, power FETs
and all other onboard components necessary to protect the cells from overcharge, overdischarge, short
circuit, and overcurrent discharge in a 8-series cell Li-Ion or Li-Polymer battery pack. The circuit module
connects directly across the cells in a battery. With a compatible interface board and Windows®-based PC
software, the user can view the bq77908A registers and program the IC configuration and protection
limits.
Contents
1 Features ...................................................................................................................... 3
1.1 Kit Contents ......................................................................................................... 3
1.2 Required Equipment ............................................................................................... 3
2 bq77908A Circuit Module and Interfaces ................................................................................ 3
2.1 Circuit Module Connections ...................................................................................... 3
2.2 Signal Descriptions ................................................................................................ 4
3 bq77908AEVM Hardware Connection and Operation ................................................................. 5
3.1 Initial Considerations .............................................................................................. 5
3.2 Connecting the Cell Simulator .................................................................................... 6
3.3 Simulated Battery Connection .................................................................................... 6
3.4 Pack Connections .................................................................................................. 6
3.5 Basic Operation .................................................................................................... 7
3.6 Cell Connections ................................................................................................... 8
4 Software Installation ........................................................................................................ 8
4.1 System Requirements ............................................................................................. 8
4.2 Interface Adapter ................................................................................................... 8
4.3 Installing the bq77908GUI or bq77910GUI Evaluation Software .......................................... 10
5 Software Operation ........................................................................................................ 10
5.1 Menu Commands ................................................................................................. 12
5.2 Working With Register Values .................................................................................. 14
5.3 Status Section ..................................................................................................... 16
5.4 Basic Operation With Software ................................................................................. 17
5.5 Operation With Other Interfaces or Hosts ..................................................................... 17
6 Related Documents From Texas Instruments ......................................................................... 18
7 bq77908AEVM Circuit Description and Configuration ................................................................ 18
7.1 Battery Voltage Clamp ........................................................................................... 18
7.2 Device Power ..................................................................................................... 18
7.3 Cell Monitor Inputs and Configuration ......................................................................... 18
7.4 Ground Connection ............................................................................................... 20
7.5 Current Sense Connections ..................................................................................... 20
7.6 Filter Capacitors .................................................................................................. 20
7.7 FET Circuits ....................................................................................................... 21
7.8 Detection Sensing ................................................................................................ 21
7.9 Output Protection Components ................................................................................. 21
Windows, Microsoft are registered trademarks of Microsoft Corporation.
Aardvark is a trademark of Total Phase, Inc.
1
SLUU854–February 2012 bq77908AEVM Evaluation Module
Submit Documentation Feedback Copyright ©2012, Texas Instruments Incorporated

www.ti.com
7.10 Reserved Pins .................................................................................................... 22
7.11 Flag Outputs ...................................................................................................... 22
7.12 Thermal Sensor ................................................................................................... 22
7.13 ZEDE ............................................................................................................... 22
7.14 Programming Interface .......................................................................................... 22
8 bq77908A Circuit Module Physical Construction ...................................................................... 23
8.1 Main Board ........................................................................................................ 23
8.2 Resistor Cell Simulator .......................................................................................... 32
List of Figures
1 Basic EVM Setup ........................................................................................................... 7
2 Successfully Updated TI USB Interface Adapter ....................................................................... 9
3 EVM Connection for Communication and Programming............................................................. 11
4 GUI With Communication Established.................................................................................. 12
5 Communication Selection Window...................................................................................... 13
6 Commands Without Communication Established..................................................................... 13
7 Register Section ........................................................................................................... 14
8 Status Section.............................................................................................................. 16
9 Polling Status With Undervoltage Condition ........................................................................... 17
10 Top Silkscreen............................................................................................................. 23
11 Top Assembly.............................................................................................................. 24
12 Top Layer................................................................................................................... 24
13 Layer 2...................................................................................................................... 25
14 Layer 3...................................................................................................................... 25
15 Bottom Layer............................................................................................................... 26
16 Bottom Silkscreen ......................................................................................................... 26
17 Bottom Assembly.......................................................................................................... 27
18 Schematic Diagram, Sheet 1 of 2 ....................................................................................... 30
19 Schematic Diagram, Sheet 2 of 2 ....................................................................................... 31
20 Resistor Simulator Top Silkscreen ...................................................................................... 32
21 Resistor Simulator Top Layer............................................................................................ 33
22 Resistor Simulator Bottom Layer........................................................................................ 34
23 Resistor Simulator Top Assembly....................................................................................... 35
24 Resistor Simulator Bottom Assembly................................................................................... 36
25 Resistor Simulator Schematic Diagram ................................................................................ 38
List of Tables
1 Ordering Information........................................................................................................ 3
2 Cell Connections............................................................................................................ 4
3 PACK Connections ......................................................................................................... 4
4 Programming Interface Connections ..................................................................................... 4
5 Test Header Signals........................................................................................................ 5
6 Control and Status Connections .......................................................................................... 5
7 Adapter Cable Pinout ..................................................................................................... 10
8 Status Section Indicator Colors.......................................................................................... 16
9 Cell Count Component Configuration................................................................................... 19
10 bq77908A Circuit Module Bill of Materials ............................................................................. 27
11 Performance Specification Summary................................................................................... 32
12 Resistor Simulator Bill of Materials...................................................................................... 36
2bq77908AEVM Evaluation Module SLUU854–February 2012
Submit Documentation Feedback
Copyright ©2012, Texas Instruments Incorporated

www.ti.com Features
1 Features
•Complete evaluation system for the bq77908A 4-series to 8-series cell Li-Ion or Li-Polymer battery
protector
•Populated circuit module for 8-cell, parallel FET configuration for quick setup
–Pads for components for configuration of additional cell counts and series FETs
•Power connections available on terminal blocks or banana jacks
•Control and status signals available on terminal blocks
•Resistor cell simulator for quick setup with only a power supply
•Personal computer software available for configuration
1.1 Kit Contents
•bq77908A circuit module
•Resistor cell simulator
•Set of support documentation
Table 1. Ordering Information
EVM Part Number Chemistry Configuration Capacity
bq77908AEVM-001 Li-Ion 8 cells Any
NOTE: Although capacity Table 1 is show as Any, practical limits of the physical construction of the
module typically limit the operation of the EVM to a 1P or 2P battery construction. See
Section 8 for board details.
1.2 Required Equipment
The following equipment is required to operate the bq77908AEVM in a simple demonstration.
•DC power supply, 0-V to 34-V at 0.5 A
•DC voltmeter or oscilloscope,
•DC power supply, ~3 V at .1 A or an approximately 15-kΩ, 1/4-W resistor
•Test leads to connect equipment
The following equipment is required to operate the bq77908AEVM with a more extensive demonstration.
•TI USB-TO-GPIO interface adapter
•Computer with USB port and compatible Windows 32-bit operating system
•Electronic load
•Additional power supplies
•TI bq77910GUI Evaluation Software (see Section 4).
2 bq77908A Circuit Module and Interfaces
The bq77908A circuit module contains the bq77908A IC and related circuitry to demonstrate the features
of the IC. A FET with heatsink is provided for the high-current discharge path. A lower current FET is
provided for the charge path. A thermistor provides temperature sensing for the device. Other components
provide support for the IC and connections to the board.
2.1 Circuit Module Connections
Connections are provided for the following interfaces:
•Direct cell connections
•PACK connections
3
SLUU854–February 2012 bq77908AEVM Evaluation Module
Submit Documentation Feedback Copyright ©2012, Texas Instruments Incorporated

bq77908A Circuit Module and Interfaces www.ti.com
• Programming interface
2.2 Signal Descriptions
Signals available on the EVM are described in this section. For details on the location and connector
types, see Section 8. High current signals can be connected at either the terminal block or banana jack.
Refer to the physical construction section for identification.
Cell connections are described in Table 2. The default board assembly supports only 5 cells, so the upper
cell connections are not used. CELL0 and CELL5 are connected to the high current paths on the board
through 0-Ωresistors. This allows operation of the resistive cell simulator without external connections. If
the onboard resistors are removed, connections must be made off the board. See Section 8 for resistor
identification. Cell connection sequence is described in Section 3.6.
Table 2. Cell Connections
Reference Pin Number Signal Description
Designator
J13, J15 All BATT–Negative electrode of first (bottom) cell, high-current connection
Negative electrode of first (bottom) cell, optional separate monitor connection to
6 CELL0 cell
5 CELL1 Positive electrode of first (bottom) cell
4 CELL2 Positive electrode of second cell
J5 3 CELL3 Positive electrode of third cell
2 CELL4 Positive electrode of fourth cell
1 CELL5 Positive electrode of fifth cell,
5 CELL6 Positive electrode of sixth cell
4 CELL7 Positive electrode of seventh cell
J4 3 CELL8 Positive electrode of eighth cell, optional separate monitor connection to cell
2 NC9 Unused connection
1 NC10 Unused connection
J10, J11 All PACK+ Most positive cell output, high-current connection, shared with PACK+
Load connections are described in Table 3.
Table 3. PACK Connections
Reference Pin Number Signal Description
Designator
Positive output of evaluation board, shared with the battery high-current
J10, J11 All PACK+ connection
J12, J14 All DSG–Negative output of evaluation board for discharge
J16, J17 All CHG–Negative input to evaluation board for charge
Programming signals are described in Table 4. J3 signals are 3.3-V logic level.
Table 4. Programming Interface Connections
Reference Pin Number Signal Description
Designator
1, 2, 5, 7, 8 Not used
3 PGM Control signal for EEPROM programming voltage.
4 ZD Control signal for device ZEDE
J3 6 GND Signal reference for the IC
9 ECLK Serial interface clock connection
10 EDATA Serial interface data connection
1 14V Regulated 14-V input for IC programming
J2 2 GND Signal reference for the IC
4bq77908AEVM Evaluation Module SLUU854–February 2012
Submit Documentation Feedback
Copyright ©2012, Texas Instruments Incorporated

www.ti.com bq77908AEVM Hardware Connection and Operation
Test header or pattern signals are described in Table 5.
Table 5. Test Header Signals
Reference Usage Pin Number Signal Description
Designator
Default: shunt installed 1 Battery feed Power feed to 100-Ωshunt resistor
for normal operation.
J1 Remove shunt for U1 2 BAT Output of 100-Ωshunt resistor to IC BAT pin
supply current
measurement 1 VREG IC regulator output
IC zero delay test point and input pin, also connected
Default: no shunt. Install 2 ZEDE
J6 to J3
shunt to hold ZEDE high Pulldown resistor for strong pulldown of ZEDE if
3 PD required
Not populated. Alternate 1 TS IC temperature sense pin
J8 test point or remote 2 GND Signal reference for the IC
thermistor connection
Control and status signals are provided on terminal blocks. These signals are described in Table 6.
Table 6. Control and Status Connections
Reference Pin Number Signal Description
Designator
1 TS IC TS signal through a resistor
J7 2 GND Signal reference for the IC
Control signal for charger detection, connects through a resistor to the IC CHGST
1 CHGCTL pin
J9 2 DSGFLAG Diode and resistor isolated DSG signal
3 CHGFLAG Diode and resistor isolated CHG signal
3 bq77908AEVM Hardware Connection and Operation
This section describes the connection of the circuit module and EVM and simple operation in its default
configuration.
3.1 Initial Considerations
Boards are tested after assembly with a basic functional test. This test may not check every connection on
the board. Boards must be checked for function in the user’s environment before relying on the safety
features of the board. Operation of the board with test equipment before connecting cells is recommended
and described in this document.
The default configuration of the board is 8 cells with parallel FETs. Modifying the EVM for different cell
counts or FET configuration requires solder connections. It is recommended that the users familiarize
themselves with operation of the board in the default configuration before modifying the board, and check
the operation of the board with test equipment after any modification. Configuration of the board is
described in Section 7.
Be sure to observe the cautions and warnings in this document.
A variety of connections are provided on the EVM. The manufacturer's rating for the terminal blocks for
Pack and Battery connections is 32 A nominal. Parallel connections are provided for high-current
operation. The banana jacks are rated at 15 A. Safety agency ratings may be lower than the manufacturer
ratings; limit currents to appropriate values for your evaluation. Cell monitor terminal blocks and the
control signal terminal blocks are rated at lower currents and must not be used for high-current paths.
5
SLUU854–February 2012 bq77908AEVM Evaluation Module
Submit Documentation Feedback Copyright ©2012, Texas Instruments Incorporated

bq77908AEVM Hardware Connection and Operation www.ti.com
A communication interface is not required for basic operation; it must be connected to the computer and
EVM circuit module only after proper installation of software. The software along with an appropriate
communication interface allows setting the programmable safety limits of the device and checking the
status after fault detection. Installation of the software and its use are described in Section 4 and
Section 5, respectively.
3.2 Connecting the Cell Simulator
The cell simulator consists of headers to mate the board and ten 200-Ωresistors to divide the battery
voltage between the inputs. Only 8 of these resistors are used for the bq77908A EVM. Power is provided
through the Cell0 and Cell8 connections on the terminal block headers. Various test points are provided
on the board. See Section 8 for additional details.
•Be certain no power is applied to the board.
•Unplug the screw terminal blocks from J4 and J5 of the EVM, and save these for later use.
•Plug the cell simulator board onto J4 and J5. Support may be required on the bottom of the EVM while
the connectors are pressed together firmly.
CAUTION
Do not connect or remove the cell simulator board while power is applied to the
EVM. The resistor pulldown or pullup from intermittent connections
over-stresses the device inputs.
3.3 Simulated Battery Connection
Connect a power supply between BATT–(negative) and PACK+ (positive). This power supply connects to
the resistor cell simulator through default connections on the bq77908A circuit module.
3.4 Pack Connections
A load or charger is connected to the pack terminals using the terminal blocks provided. It is
recommended that the load or charger be connected with the current switched off to prevent arcing or
transients during connection of the wires to the terminal blocks. Charger detection is required for the
bq77908A with a signal at the CHGST pin. Charger detection can be provided by connecting a resistor
from the CHGCTL terminal of the board to the PACK supply, or with a logic level voltage supply for
evaluation. An external resistor is required due to the low resistance pulldown on the board. The selected
resistor must keep the CHGST voltage above the VCHG_DET1 data sheet threshold over the entire
evaluation voltage range while limiting the power in the 1-kΩpulldown resistor to 1/16 W or less. A 15-kΩ,
1/4-W resistor is typically suitable for the default configuration; a smaller value may be required for low
voltage or if the configuration is changed.
WARNING
The CHGCTL must not be tied to the power supply without the
external resistor because the 1-kΩresistor on the board becomes
very hot and may damage the board.
Although designed for 30-A operation, the board may not dissipate enough power to operate without
exceeding all component ratings. The user must monitor the temperature of the board and components
during evaluation and provide cooling air and/or heatsinks as required for operation. The thermal sensor
on the board may not respond to protect the FETs from damaging temperatures due to its location and
possible thermal gradients on the board.
6bq77908AEVM Evaluation Module SLUU854–February 2012
Submit Documentation Feedback
Copyright ©2012, Texas Instruments Incorporated

“Charger”
supply
+
-
Resistor
Cell
Simulator
“Battery”
supply
+
-
~ 15k ohm
Load+
-
www.ti.com bq77908AEVM Hardware Connection and Operation
CAUTION
The bq77908A circuit module may be damaged by overtemperature. To avoid
damage, monitor the temperature during evaluation, and provide cooling as
needed for your system environment.
WARNING
The bq77908A circuit module may become hot during operation
due to dissipation of heat. Avoid contact with the board. Follow all
applicable safety procedures applicable to your laboratory.
CAUTION
Some power supplies can be damaged by application of external voltages. If
using more than one power supply, check your equipment requirements, and
use blocking diodes or other isolation techniques as needed to prevent damage
to your equipment.
The connection of the EVM looks similar to Figure 1.
Figure 1. Basic EVM Setup
3.5 Basic Operation
The following steps are suggested for basic operation of a default EVM with the cell simulator and the
default configuration in EEPROM.
1. Confirm that the cell simulator board is installed on the EVM.
2. Connect a power supply between the BATT–(negative) and PACK+ (positive) terminals.
3. Connect a 15-kΩ, 1/4-W resistor to the CHGCTL terminal of the board.
4. Set the bench supply to approximately 29 V.
5. Connect a disabled load between the DSG–(negative) and PACK+ (positive) terminals.
6. Wake up the part by momentarily connecting the 15-kΩresistor to the bench supply positive.
7
SLUU854–February 2012 bq77908AEVM Evaluation Module
Submit Documentation Feedback Copyright ©2012, Texas Instruments Incorporated

Software Installation www.ti.com
7. Monitor the CHG and DSG test points using a meter or oscilloscope as desired.
8. Enable the load with a nominal 0.2-A or other current within the capability of the supply.
9. Increase the bench supply voltage to approximately 34 V, and observe that the CHG test point goes
low.
10. Reduce the voltage to approximately 29 V, and observe that the CHG test point returns high.
11. Decrease the voltage to approximately 20 V, and observe that the DSG test point goes low and the
load current drops. The device shuts down after 9 seconds at low voltage.
12. Remove the load, and connect the CHGCTL resistor to the supply to simulate a charger.
13. Increase the supply voltage to approximately 29 V, and observe that the DSG test point goes high,
and if the load is re-connected, that current flows again.
3.6 Cell Connections
For initial evaluation, it is suggested power supplies be used for cell simulation to observe the behavior of
the device. An isolated power supply with a resistor connected across its terminals may be connected to
test points on the resistor simulator to vary the voltage above or below the voltage of the other cells, or a
similar configuration may be used. The smaller the resistor value, the more current is required from the
battery simulator power supply and the smaller the influence on the voltages if cell balancing is operated.
Whether power supplies or cells are used, inductance in the high-current path must be minimized.
Inductance in this path can cause inductive transients at the board when the load current is stopped or the
bq77908A opens the discharge FET with current flow. Use heavy-gauge wires for the high-current
connections; minimize inductances by keeping leads close together.
When connecting cells to the EVM, the user must use care not to exceed the absolute maximum ratings of
the device. The bq77908A is designed with open-cell (wire) detection; however, fixturing must not pull
unconnected signals up or down. Signal reference (VSS) for the part is from the BATT–terminal of the
EVM, and this lowest potential must be connected first. Cells must be connected in sequence from lowest
to highest voltage as described in the data sheet. When terminating the cells to the removable terminal
blocks prior to connection to the EVM, the following steps are recommended:
1. Be sure the charger and any load is disconnected (CHGCTL is open).
2. Connect the cell stack negative high-current terminal to the EVM BATT–terminal.
3. Connect the lower cell group to the J5 connector.
4. Connect the upper cell group to the J4 connector.
5. Connect the cell stack positive high-current terminal to the EVM PACK+ terminal.
6. When removing cells, remove any charger and CHGCTL connection, then disconnect in the reverse
order.
4 Software Installation
This section describes how to install the software for the bq77908AEVM-001.
The BQ77908-10-GUI SW supports the bq77908A, and is described in this document as bq77908A
evaluation software.
4.1 System Requirements
The bq77908A evaluation software requires a 32-bit version of Windows XP, Windows Vista, or Windows
7. The computer must also have Microsoft®.NET framework version 2.0 or higher installed. Examples in
this document are from Windows XP.
4.2 Interface Adapter
The bq77908A evaluation software supports either the TI USB-TO-GPIO adapter (TI USB Interface
Adapter) or the Total Phase Aardvark™to provide communication with the EVM board from the computer.
The Total Phase Aardvark must be selected if desired. The EVM connector supports the TI USB Interface
Adapter; a special cable must be constructed if you wish to use the Aardvark.
8bq77908AEVM Evaluation Module SLUU854–February 2012
Submit Documentation Feedback
Copyright ©2012, Texas Instruments Incorporated

www.ti.com Software Installation
4.2.1 TI USB Interface Adapter
The TI USB Interface Adapter is the default option for the bq77908A evaluation software. Its pinout is
compatible with the bq77908AEVM board J3 connector.
The TI USB Interface Adapter http://focus.ti.com/docs/toolsw/folders/print/usb-to-gpio.html is actually a
separate EVM from Texas Instruments, and its default firmware is not compatible with the bq77908A. If
the firmware has already been updated to version 2.0.19 to work with other BMS-HCE products, additional
update is not required. If required, update the firmware using the following steps.
1. Obtain the USB-to-GPIO EVM Firmware Loader from
http://focus.ti.com/docs/toolsw/folders/print/usb2gpio-loader-sw.html, or search from power.ti.com
2. Download, extract, and run the installer
3. Installation requires the Microsoft .NET connection software. If a suitable version is not found on the
system by the installer, the user is prompted to obtain and install .NET.
4. Connect the TI USB Interface Adapter to the computer with the USB cable. The green LED illuminates.
5. Run the program, typically from Start →Run →Texas Instruments →USB-TO-GPIO Firmware
Loader.
6. Detailed instructions are provided in the Readme.txt file.
CAUTION
Do not disconnect the USB cable to the Interface Adapter during firmware
update. Loss of power may leave the adapter with corrupt firmware and be
unable to further update the firmware.
7. If you want to be able to return to the original configuration, back up the installed firmware before
update.
8. Load and update to the 2.0.19 version using the instructions provided.
9. If an error occurs, do not unplug the adapter. Re-try loading, load a different firmware, or re-start the
software and repeat until a load is successful.
10. After successful update, the window appears as is shown in Figure 2
11. After update, exit the program.
Figure 2. Successfully Updated TI USB Interface Adapter
9
SLUU854–February 2012 bq77908AEVM Evaluation Module
Submit Documentation Feedback Copyright ©2012, Texas Instruments Incorporated

Software Operation www.ti.com
4.2.2 Aardvark Adapter
Although the Total Phase Aardvark adapter can physically mate to the EVM J3 connector, the pinout is
incompatible. A special interface cable must be constructed to use the Aardvark. Refer to the schematics
and Table 7 below for information.
CAUTION
Do not connect the Aardvark to the EVM without a properly constructed cable.
Damage may result to the EVM and/or Aardvark.
Table 7. Adapter Cable Pinout
USB-TO-GPIO (Mates to J3) Aardvark
IC Pin Name
or Description Pin Signal Pin Signal
VSS –signal 6 GND 2 GND
reference
SCLK 9 SCL 1 SCL
SDATA 10 SDA 3 SDA
ZEDE –
communication 4 GPIO4 5 MISO/GPIO
enable
Programming
voltage control 3 GPIO5 7 SCLK/GPIO
signal for
EEPROM
4.3 Installing the bq77908GUI or bq77910GUI Evaluation Software
Get the latest software version in the bq77908 and bq77910 GUI Evaluation Software tool
folder:http://www.ti.com/tool/bq77908-10-gui-sw, or search from power.ti.com. Check periodically for
software updates. Use the following steps to install the bq77908A Evaluation Software:
1. Copy the archive file to a directory of your choice; extract and run the bq77910 Setup.msi installer.
2. Follow the instructions, and make selections as required on the setup windows, selecting next as
required.
3. On the last window, select "close" to complete the bq77910 software installation.
5 Software Operation
This section describes connection of the communication interface to the EVM and operation of the
software.
Although the software will run without connection to a powered device, it is recommended to have the
device on when starting the software. Figure 3 shows connections for operation with the GUI software.
10 bq77908AEVM Evaluation Module SLUU854–February 2012
Submit Documentation Feedback
Copyright ©2012, Texas Instruments Incorporated

“Charger”
supply
+
-
Resistor
Cell
Simulator
USB
Interface
Adapter
PC
“Battery”
supply
+
-
USB
~ 15k ohm
“Programming”
supply
(14V)
+
-
Load+
-
www.ti.com Software Operation
Figure 3. EVM Connection for Communication and Programming
To connect the computer to the GUI and start the software, use the following steps:
1. Connect the TI USB interface adapter to the computer.
2. Connect the 10-pin connector from the interface adapter to the EVM J3.
CAUTION
The communication interface is not isolated on the EVM. Be sure no ground
potential exists between the computer and the EVM. Also be aware that the
computer is referenced to the battery-potential of the EVM.
3. Remove any shunt installed on J6 so that the interface can control ZEDE.
4. Connect the battery power supply to the EVM, and adjust to approximately 29 Vdc.
5. Wake the bq77908A by connecting CHGCTL high.
6. Start the software, typically using Start →All Programs →Texas Instruments →bq77908A Evaluation.
When started, the software looks for the communication interface and the device. When communication is
established with the device, the main window appears as shown in Figure 4. The software copies the
EEPROM to the volatile registers.
11
SLUU854–February 2012 bq77908AEVM Evaluation Module
Submit Documentation Feedback Copyright ©2012, Texas Instruments Incorporated

Software Operation www.ti.com
Figure 4. GUI With Communication Established
Other than the menu selections, the software window has three sections. In the bottom border is a status
section. The middle section is a register section. The top section has a selection for the device used and a
status area useful for checking the device status when a fault is detected. Details are described in
following sections.
5.1 Menu Commands
5.1.1 Help Menu
The Help →About menu selection displays version information about the program.
5.1.2 Setup Menu
The Setup →Communication selection allows selection of either the USB Interface Adapter or the
Aardvark. Default is the TI USB Interface Adapter, and this window is not needed. Selecting the Save and
Exit button checks for the adapter. If the selected adapter is not present, a communications error window
appears. Selecting OK in the window returns to the Communication Selection window. To exit without
having the selected adapter connected, use the close window tool (red X button). Selection of an adapter
other than the two shown is not supported.
12 bq77908AEVM Evaluation Module SLUU854–February 2012
Submit Documentation Feedback
Copyright ©2012, Texas Instruments Incorporated

www.ti.com Software Operation
Figure 5. Communication Selection Window
5.1.3 Commands Menu
Most commands are only available after communication is established with the device. Figure 6 shows the
command window when communication is not yet established.
Figure 6. Commands Without Communication Established
The communication status in the bottom border of the window shows the adapter in use and the device
communication status. If the software is started and the adapter is not found, a Communication Error
message box is displayed. Selecting OK on the box displays the main window. If the device is not
recognized, a Device Not Found box is displayed. Selecting OK to this box also displays the main window.
The communication fault is displayed in the status area of the window. Communication can be re-tried by
selecting the menu command Commands →Find Target. Once communication is established with the
part, the Find Target command is no longer available.
The other commands relate to the register section. The register section is shown in Figure 7. Two sets of
registers are displayed: the right section can display the EEPROM settings, and the left side can display
the volatile registers waiting to be programmed in the EEPROM. When the software is first started, all
values are shown as zero. When the software is started and connects to the device, it will copy the
EEPROM values to the volatile registers. The software does not know if power has been removed from
the part and will continue to display the values, even though the device may have different values.
Registers should be read before use.
13
SLUU854–February 2012 bq77908AEVM Evaluation Module
Submit Documentation Feedback Copyright ©2012, Texas Instruments Incorporated

Software Operation www.ti.com
Figure 7. Register Section
The Read Volatile Registers command reads the values from the registers in the part and displays them in
the GUI window. When a part is first powered, these are typically zero. When connecting to a powered
part, they likely contain residual values.
The Read EEPROM Registers command reads the EEPROM values from the device and displays them in
the EEPROM registers section of the window for viewing. This is a viewing operation, and data
manipulation is not allowed in the displayed EEPROM data.
The Read All Registers command reads both the volatile and EEPROM registers from the device and
displays the values.
The Copy EEPROM to Volatile command copies the EEPROM register values to the corresponding
volatile registers and displays both in the GUI. This is a good starting point for making incremental
changes to the device settings.
The Verify Volatile Registers command checks whether the volatile registers match the contents of the
device. This can be useful as a check before programming the EEPROM.
The Program EEPROM command writes the volatile register values
5.1.4 File Menu
The Load Registers from File command reads a properly formatted file and fills the volatile register section
with the values. This is useful for loading a device with a saved configuration. A windows navigation tool
allows selection of the file. Whereas files can be edited, it is recommended to load files saved by the
software, and if any editing is performed on the file, check all values before programming the device.
The Save Registers to File command creates a file. A windows navigation tool allows selection of the
location and file name. Files have the .cfg extension.
The Exit command exits the program.
5.2 Working With Register Values
When the software initially connects to a device it will copy that device's EEPROM to its volatile registers
and display those results. Since the device does not know if power has been lost to the device, the
register display may be stale. If the device has been changed or power cycled to the part, the registers
should always be read before making changes. If a file is loaded with values matching the displayed
values, the software will not know the data is different from the part. Reading the registers or copying
EEPROM values to the volatile registers is recommended before any change.
14 bq77908AEVM Evaluation Module SLUU854–February 2012
Submit Documentation Feedback
Copyright ©2012, Texas Instruments Incorporated

www.ti.com Software Operation
EEPROM values are displayed but are not directly editable in either the device or the GUI. Changes are
made to a volatile register set by changing the volatile register value which is written to the volatile register
in the device and later written to the device EEPROM by the programming process. Changes in the
volatile registers do not affect operation of the device until written into the EEPROM.
The software does not know the difference between the bq77908A and bq77910A. The user must select
the device connected with the selection buttons in the top section of the window. Selecting the bq77908A
will add some limit checking for the SYS_CFG CNF field to avoid programming an invalid configuration
into the device. Attempting to program an invalid configuration with the bq77908A selected will display an
error box and will not program the part. The devlce selection also changes the device name in saved
configuration files.
Values in the Volatile Registers section can be typically be changed in three ways:
•Loading a register file
•Changing a check box or drop-down selection
•Entering a data value in the box corresponding to the register name
The SYS_CFG register bits are displayed as selection boxes; these are green for a value 0 and orange for
a value 1.
The following steps describe changing a device EEPROM setting on the EVM using the GUI with a
connected adapter:
1. Power the EVM (device) with the battery supply, and wake it up with charger detection.
2. Maintain a logic high on the CHGCTL pin of the EVM (CHGST device pin).
3. Copy the EEPROM values to the volatile registers with the Copy EEPROM to Volatile command.
4. Edit the values in the Volatile Registers section as desired.
5. Provide a 14 V ±0.5 V at approximately 0.1-A programming voltage at the EVM J2 connector.
6. Select the Program EEPROM command.
7. After a short delay, a programming complete status window appears. Select OK in this window.
8. Disconnect the programming voltage from the EVM J2 connector.
Programming the EEPROM from a file uses a similar sequence. This can be useful in evaluation when
replacing a device or duplicating a design on a small number of boards. The following steps describe
programming a device EEPROM on the EVM from a saved configuration file using the GUI with a
connected adapter:
1. Power the EVM (device), and wake it up with charger detection.
2. Maintain a logic high on the CHGCTL pin of the EVM (CHGST device pin).
3. Copy the EEPROM values to the volatile registers with the Copy EEPROM to Volatile command if the
software is not restarted for each device.
4. Select the File →Load Register File command, navigate to, and open the desired file.
5. Provide a 14 V ±0.5 V at approximately 0.1-A programming voltage at the EVM J2 connector.
6. Select the Program EEPROM command.
7. After a short delay, a programming complete status window appears. Select OK in this window.
8. Disconnect the programming voltage from the EVM J2 connector.
After programming, it may be necessary to clear fault status because programming requires
communication with the device and that requires setting ZEDE high. ZEDE high may make the part
respond to noise. SCC is typically the lowest value threshold in the device and is common after
programming or other communication with the part, depending on the device settings and operating
environment.
15
SLUU854–February 2012 bq77908AEVM Evaluation Module
Submit Documentation Feedback Copyright ©2012, Texas Instruments Incorporated

Software Operation www.ti.com
CAUTION
Although the software may be useful for producing a small number of boards, it
is not intended as a production programming tool. Accidental manipulation of
the registers when the file is loaded and when the programming command is
sent is not prohibited.
During programming, the software checks that the device volatile registers match the values shown. If
they do not match, an error message is displayed. Continuing with programming when the values do not
match will unexpectedly alter the configuration of the device. If the error is displayed, it is recommended to
read the volatile registers to examine the contents, correct any communication error, and re-start the
software or device as needed for proper programming.
5.3 Status Section
The status section of the GUI is shown in Figure 8. This section allows the user to display internal status
registers of the devices fault condition. This data is not part of normal operation of the device and is not
shown in the data sheet. Accessing the data is disruptive to the device; however, it can be beneficial in
evaluation.
Figure 8. Status Section
The status is read by selecting the Polling Enable button on the left side of the status section. This
periodically sets ZEDE high to the device, reads the status registers, and returns ZEDE low. The polling
period can be selected with the drop-down box next to the button. The button function and label change to
Disable. The button label indicates the action of the next button actuation.
A consequence of polling is that a pending fault delay is terminated by the status read. Polling is typically
independent of any system change, and a fault may be recorded as soon as the poll occurs. This may
lead to unexpected results in evaluation. The following text describes a couple examples which can occur:
•The user has selected a 2-second undervoltage delay and wants to observe the timing on a scope.
The user leaves polling active and decreases the device voltage. The poll occurs just after the voltage
drops, and the zero delay causes the fault to be registered. The FETs turn off and the user thinks the
delay setting is not working. This situation occurred because the poll set ZEDE high and terminated the
undervoltage delay.
•The user is polling status to watch faults. CHGST is tied high to prevent the part from shutting down
due to undervoltage. The user begins switching currents and is surprised when a SCC fault occurs.
Observing the sense resistor voltage, the user does not see a charge current. This situation occurred
because the poll set zero delay and eliminated noise filtering on the current. The SCCT is typically a
low and thus most sensitive to any noise; having CHGST high prevents recovery from the fault.
The values display in several colors. See Table 8.
Table 8. Status Section Indicator Colors
Color Meaning
Gray Status is not read
Device is polling and status is normal with connected device, or adapter is not
Bright green connected
Bright red Device is polling and status is fault
Dark green or dark red Device is not polling and value is residual from last poll
16 bq77908AEVM Evaluation Module SLUU854–February 2012
Submit Documentation Feedback
Copyright ©2012, Texas Instruments Incorporated

www.ti.com Software Operation
Figure 9 shows a typical status display polling with undervoltage.
Figure 9. Polling Status With Undervoltage Condition
Another use of the status section is to determine the reason the part has turned off the FETs. For
example, if during test the EVM has turned off the FETs but the VREG is still on, the interface might be
connected and the status polled to see what fault the device identifies.
5.4 Basic Operation With Software
The following steps are suggested for exercising more of the device features using the EVM in its default
8-cell configuration and EEPROM settings. The board is connected as shown in Figure 3. Remember that
timing as described in Section 5.3 will be incorrect.
1. Install the software.
2. Connect the USB Interface Adapter to the computer with the USB cable.
3. Remove the screw terminal blocks from J4 and J5, and save for later use. Connect the cell simulator
board to the bq77908A main board J4 and J5. Support the under side of the EVM board as the
connectors are pressed together.
CAUTION
Do not connect or remove the resistive cell simulator from the board with power
applied. The resistor pulldown or pullup from intermittent connections
over-stresses the device inputs.
4. Connect the 10-pin ribbon cable from the USB Interface Adapter to the EVM J3.
5. Connect an isolated power supply negative to BATT–and positive to PACK+. Adjust the voltage to
approximately 29 V.
6. Connect an approximate 15-kΩresistor from the power supply positive to the CHGCTL terminal. This
wakes up the part; leave the resistor connected.
7. Start the software.
8. Connect a disabled load to the pack terminals.
9. Select the Polling Enable button in the software window.
10. Observe that the status values are bright green.
11. Set a current on the load within the capability of the supply and board.
12. Decrease the power supply voltage to approximately 20 V. Observe that using the load current stops,
and the UV status indicator turns red.
13. Increase the supply voltage to approximately 29 V. Observe that the UV indicator turns green.
14. Load current may not resume until the load is disabled or disconnected.
15. Increase the supply voltage to approximately 34 V. Observe that the OV status indicator turns red.
16. Decrease the power supply voltage to approximately 29 V. Observe that the OV indicator turns green.
17. Disable polling.
18. Disable the load
19. Set the supply to 0 V, and turn off equipment.
5.5 Operation With Other Interfaces or Hosts
The bq77910 GUI software does not support other interfaces.
17
SLUU854–February 2012 bq77908AEVM Evaluation Module
Submit Documentation Feedback Copyright ©2012, Texas Instruments Incorporated

Related Documents From Texas Instruments www.ti.com
Communication with the bq77908A from other hosts must be straightforward. See to the data sheet for
timing and interface details. On the EVM, zero delay mode can be set to allow communication using a
0.1-inch shunt (not provided) at J6 pins 1 to 2, or a signal at ZD on J3. To program, the onboard
programming voltage switch can be used by controlling the PGM signal on J3. Signals must be 3.3-V
CMOS levels.
6 Related Documents From Texas Instruments
To obtain a copy of any of the following TI document, call the Texas Instruments Literature Response
Center at [phone] or the Product Information Center (PIC) at [phone]. When ordering,
identify this document by its title and literature number. Updated documents can also be obtained through
the TI Web site at www.ti.com
Document Literature Number
bq77908A Multi-Cell Lithium-Ion/Polymer Precision Protector SLUSAV5
Data Sheet
7 bq77908AEVM Circuit Description and Configuration
This section describes the circuit on the bq77908A circuit module and how to configure it for changes the
user may want to make to the board for specific evaluations. In many cases, an EVM schematic is used
as a starting point for a circuit design. This can result in unnecessary extra components on the product
design that take up space and add cost. Refer to the schematic in Section 8 while reading the following
descriptions. Note that the schematic has two pages: the first shows the main functions, and the second
page shows primarily cell count configuration and protection components.
7.1 Battery Voltage Clamp
The TVS diode D9 provides a clamp for transients on the pack. A common transient is due to system
inductances and sudden load shutoff. The breakdown voltage of D9 must be set near or below the 5-V per
cell absolute maximum of the device. As a transient pushes the voltage up the I-V curve, a substantial
device here reduces the demands on other clamping components in the system, which may be needed to
protect the device. Alternatives to D9 may be to control the system inductance and current switching rate,
use capacitance to absorb transients, or other transient protectors such as MOVs where appropriate.
7.2 Device Power
The device is powered through the BAT pin. C12 is a bypass capacitor near the IC; the footprint is large in
order to make it easy to mount larger capacitors, in the event that this is desired in evaluation. R5 and J1
provide a way to measure current to the device during evaluation and are not needed in an application. D2
provides power from the battery to the IC and prevents the IC power from being pulled down when the
battery voltage dips suddenly due to a heavy load on the battery. C2 provides an operating reservoir for
device current during battery voltage droop. D1 limits the voltage to the BAT pin preventing overvoltage
from rectification of transients by D2.
Power is provided through R4. The 200-Ωresistor provides for a voltage drop when an overvoltage
charger pulls down BAT through D8. For lower cell counts, this resistor may be a smaller value. R3 is a
0-Ωconnection to the high-current battery positive connection BATT+ which is shared with the PACK+.
This jumper is provided in case the user wants to power the part from the current monitor line instead.
7.3 Cell Monitor Inputs and Configuration
The cell monitor inputs are provided through an RC filter network. The series resistors RVCX connect the
cells to the device to allow voltage measurement and limit the balancing current. Balancing current is
approximately the cell voltage divided by twice the resistor. The EVM is circuit-designed to use the internal
balancing path at near the maximum current. The 47-ΩRVCX value on the EVM is nominally within 10% of
the 50-Ωminimum recommended in the data sheet and prevents exceeding the absolute maximum
balancing current up to 4.3 V per cell. The input capacitance is typically connected between cell inputs,
except the capacitances at VC8 and VC9 are connected to ground to avoid pushing the inputs below
ground during transients. The capacitance must not be increased beyond the 1 µF shown because the
18 bq77908AEVM Evaluation Module SLUU854–February 2012
Submit Documentation Feedback
Copyright ©2012, Texas Instruments Incorporated

www.ti.com bq77908AEVM Circuit Description and Configuration
capacitors are discharged into the device during balancing. The filter effect both reduces cell transients to
the device inputs and slows voltage recovery after balancing. The resulting time constant is complicated
due to the multiple components but relatively short due to the small resistors used for high balancing
current. Due to the cell input voltage measurement after balancing, the time constant (RVCX) must not be
made too large.
Note that two limits are implied by the absolute maximum cell-to-cell differential rating of the part. One is
the applied differential voltage, or 5 V on any cell regardless of the other inputs. Note also that this is an
applied voltage, not the voltage induced by the part during balancing, which may be higher. The second
voltage limit is the voltage to ground the cumulative voltage from summing the individual limits. Because
the input filter time constant is small, clamping the inputs to safe values may be required. While a Zener or
TVS diode per cell may be a suitable way to protect the device in some applications, the EVM provides
patterns D14 to D18 to clamp the inputs for cells 8 to 4 to ground. The top cell input is clamped (VC1 with
D14 on the EVM), and cell 4's input, VC7, is clamped with D18 on the EVM because this input showed
more sensitivity than others in testing. For nominal transients, these clamps along with the capacitors
between cells hold the inputs to safe values; however, different or additional clamping may be required in
evaluation or the target application.
The EVM has resistor jumper positions and is populated to connect to the cells with N+1 wires where N is
the number of cells. R42 connects the high-current BATT–connection to the lowest cell monitor point.
Similarly, R57 connects cell 8 input to the high-current path through R3. Additional resistor patterns R53 to
R58 allow the same connections when the board is configured for other series cell counts. The board may
be configured to monitor the cell voltages directly at the cells (N+3 wires) by removing R42 and R59 or the
equivalent.
When configuring the part for fewer than 8 cells, the unused inputs must not be left floating and must be
connected to avoid exceeding absolute maximums. The EVM provides patterns to allow flexible
connections. The unused pin group may be connected together on the EVM by shorting the capacitors
between them or shorting the appropriate resistor jumper positions R62 to R64. The unused pin group
then needs to be connected to a safe level, either to the top cell through one of the unused cell RVCX
patterns or to the highest used VCx pin using the appropriate R63 to R65. When configuring for fewer
than 8 cells and using the cell simulator, be sure to remove components to avoid parallel paths. Due to the
flexibility allowed by the EVM for configuration, it is recommended evaluators study the schematic before
modifying the board to achieve their desired configuration. Table 9 shows possible configurations for
different cell counts assuming use of the cell simulator, retaining the N+1 wiring plan, and adjusting the
transient protection. The board operates at a lower cell count without the transient protection adjustment,
but users must be sure they provide adequate protection for the IC in the evaluation and system design to
prevent damage. The table describes a change from the 8-cell default to one of the other configurations.
The users must check configurations if multiple changes are made. D14 is shown removed in the table for
less than 8 cells to avoid any possible leakage current or unexpected clamp during evaluation.
Table 9. Cell Count Component Configuration
Cell Count/
Reference 8 Cells (Default) 7 Cells 6 Cells 5 Cells 4 Cells
Designator
C6 Installed Remove Installed Installed Installed
C7 Installed Installed Remove Installed Installed
C8 Installed Installed Installed Remove Installed
C9 Installed Installed Installed Installed Remove
D1 Installed <35 V <30 V <25 V <20 V
D9 Installed <35 V <30 V <25 V <20 V
D14 Installed Remove Remove Remove Remove
D15 — < 35 V ———
D16 — — < 30 V — —
D17 — — — < 25 V —
D18 Installed Installed Installed Installed Installed
R18 Installed Remove Remove Remove Remove
R19 Installed Installed Remove Remove Remove
19
SLUU854–February 2012 bq77908AEVM Evaluation Module
Submit Documentation Feedback Copyright ©2012, Texas Instruments Incorporated

bq77908AEVM Circuit Description and Configuration www.ti.com
Table 9. Cell Count Component Configuration (continued)
Cell Count/
Reference 8 Cells (Default) 7 Cells 6 Cells 5 Cells 4 Cells
Designator
R20 Installed Installed Installed Remove Remove
R21 Installed Installed Installed Installed Remove
R53 — — — — 0Ω
R54 — — — 0Ω —
R55 — — 0Ω — —
R56 —0Ω — — —
R57 Installed Remove Remove Remove Remove
R62 —100 Ω0Ω0Ω0Ω
R63 — — 100 Ω0Ω0Ω
R64 — — — 100 Ω0Ω
R65 — — — — 100 Ω
The cell count programmed in the EEPROM must match the physical connection for proper operation. If
the device is programmed for more than the connected cells, the unused cells are still checked by the
device and show undervoltage or open-cell faults. If the device is programmed for fewer than the
connected cells, the upper cells are ignored and faults on these cells are not checked. Also be aware that
the voltage applied to the part can exceed the absolute maximum or show undervoltage when used with
the resistor simulator.
WARNING
When the device is configured for fewer than the connected cells,
the device does not monitor the upper cells and does not protect
against faults on those unmonitored cells.
7.4 Ground Connection
The IC VSS (ground) reference on the bq77908AEVM-001 circuit module is connected to the BATT–at
the sense resistor. Note the range of the inputs when considering moving the ground location in an
application design. The ground connection must be made at one location on the high-current path to avoid
differential voltages on the board ground due to high currents.
7.5 Current Sense Connections
R50 and R52 in parallel make the current sense resistor. Two resistors allow for lower heat dissipation per
component at a given current and allow flexibility in evaluation. R43 and R44 isolate the sense input pins
from the current path transients; C20 and C25 provide filtering. Be aware that C20 and C25 add a time
delay to the system current response depending on where sense resistor voltage falls in relation to the
threshold voltage. A mismatch in C20 and C25 can convert a common-mode signal to a differential signal
at the device pins; the C22 pattern is available if a differential filter is desired.
7.6 Filter Capacitors
The regulator filter capacitor C17 value of 4.7 µF exceeds the minimum data sheet value of 1 µF. The
1-µF DCAP and CCAP filter capacitors C21 and C26 are the data sheet recommended typical values
20 bq77908AEVM Evaluation Module SLUU854–February 2012
Submit Documentation Feedback
Copyright ©2012, Texas Instruments Incorporated