Texas Instruments bq76925EVM User manual

User's Guide
SLUU514–July 2011
bq76925EVM Evaluation Module
This user's guide for the bq76925EVM evaluation module can assist designers in their evaluation of the
bq76925, Analog Front End for 3- to 6-Series Lithium-Ion Cells. This guide discusses setup and operation
of the module and contains schematics, bill of materials, and printed-circuit board layout.
Before designing a battery management system with the bq76925, designers are advised to read the
bq76925 data sheet (SLUSAM9).
Contents
1 Overview ..................................................................................................................... 4
1.1 Features ............................................................................................................. 4
1.2 Kit Contents ......................................................................................................... 4
1.3 Equipment Requirements ......................................................................................... 4
2 Circuit Details and Configuration .......................................................................................... 6
2.1 Connections ........................................................................................................ 6
2.2 Configuration Jumpers and Switches (J1 –J6, S2, S4) ...................................................... 8
2.3 Pushbuttons (S1, S3) ............................................................................................ 10
2.4 Test Points ........................................................................................................ 10
2.5 bq76925 ........................................................................................................... 11
2.6 MSP430F2122 .................................................................................................... 11
3 Quick-Start Demonstration ............................................................................................... 11
3.1 Evaluation Software and USB-TO-GPIO Adapter ............................................................ 11
3.2 Configuration Switches and Jumpers .......................................................................... 12
3.3 Power to the bq76925EVM ...................................................................................... 12
3.4 Connect USB-TO-GPIO Adapter ............................................................................... 12
3.5 bq76925 Evaluation Software ................................................................................... 13
4 Control Register Demonstration ......................................................................................... 16
4.1 View Control Registers .......................................................................................... 16
4.2 Control Registers Introduction .................................................................................. 18
4.3 Modifying Control Registers ..................................................................................... 19
4.4 Sleep Mode and Wake Up ...................................................................................... 19
5 Control Panel Demonstration ............................................................................................ 21
5.1 Access to the Control Panel .................................................................................... 21
5.2 Measurement Tab ................................................................................................ 22
5.3 Analog Output Section ........................................................................................... 22
5.4 VCOUT Readings ................................................................................................ 23
5.5 VIOUT Readings .................................................................................................. 23
5.6 Auto Control ....................................................................................................... 23
5.7 EEPROM Correction Registers ................................................................................. 24
5.8 Startup Config Tab ............................................................................................... 24
5.9 Configuration Control ............................................................................................ 24
5.10 Power Control ..................................................................................................... 25
5.11 Logging Tab ....................................................................................................... 25
5.12 Log File ............................................................................................................ 26
Adobe, Reader are trademarks of Adobe Systems Incorporated.
Pentium is a trademark of Intel Corporation.
Mentor Graphics, PADs are trademarks of Mentor Graphics Corporation.
Microsoft, Windows, Excel are trademarks of Microsoft Corporation.
I2C is a trademark of Philips Electronics N.V..
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5.13 Log File Options .................................................................................................. 26
5.14 Enable/Disable Logging ......................................................................................... 26
5.15 Log File Example ................................................................................................. 26
5.16 Communications Tab ............................................................................................ 27
5.17 Monitor Window ................................................................................................... 27
5.18 Transactions During a Connect to Device Command ....................................................... 28
5.19 I2C .................................................................................................................. 29
5.20 I2C Register Read ................................................................................................ 29
5.21 I2C Register Write ................................................................................................ 29
5.22 I2C Communications With MSP430F2122 .................................................................... 29
5.23 Example of I2C Communications from MSP430F2122 ..................................................... 30
6 3-, 4-, and 5-Cell Operation .............................................................................................. 31
6.1 Introduction ........................................................................................................ 31
6.2 Using Onboard Cell Simulator .................................................................................. 31
6.3 Five-Cell Operation ............................................................................................... 31
6.4 Four-Cell Operation .............................................................................................. 32
6.5 Three-Cell Operation ............................................................................................. 32
7 Operation With Cells ...................................................................................................... 32
7.1 Preparing Circuit for Operation ................................................................................. 32
7.2 Battery Connection Sequence .................................................................................. 33
7.3 Six-Cell Operation ................................................................................................ 33
7.4 Five-Cell Operation ............................................................................................... 33
7.5 Four-Cell Operation .............................................................................................. 33
7.6 Three-Cell Operation ............................................................................................. 34
7.7 Battery Removal Sequence ..................................................................................... 34
8 Schematic and Bill of Materials .......................................................................................... 34
8.1 Schematics ........................................................................................................ 35
8.2 Bill of Materials .................................................................................................... 37
9 Printed-Circuit Board ...................................................................................................... 38
List of Figures
1 Home Screen of the Evaluation Software.............................................................................. 13
2 Poll Button in the Evaluation Software.................................................................................. 13
3 Poll Button in the Evaluation Software.................................................................................. 14
4 Demo With Two Power Supplies........................................................................................ 15
5 Voltage, Temperature, and Current Measurement in the Evaluation Software ................................... 15
6 Select Cell Count Set to Three Cells ................................................................................... 16
7 Volatile Control Registers Checkbox.................................................................................... 16
8 Volatile Control Registers Access....................................................................................... 17
9 Volatile Control Registers Bit Legend................................................................................... 18
10 Sleep Mode Showing 3.3-V Status...................................................................................... 20
11 Wake Up From Sleep Mode ............................................................................................. 20
12 Open Control Panel ....................................................................................................... 21
13 Control Panel Details ..................................................................................................... 21
14 Measurement Tab in the Control Panel ................................................................................ 22
15 Startup Config Tab in the Control Panel................................................................................ 24
16 Change to the Current Comparator Threshold to 175 mV at Start-Up............................................. 25
17 The Logging Tab .......................................................................................................... 26
18 Communications Tab ..................................................................................................... 27
19 Schematic –Page 1 of 4 ................................................................................................. 35
20 Schematic –Page 2 of 4 ................................................................................................. 36
21 Schematic –Page 3 of 4 ................................................................................................. 36
22 Schematic –Page 4 of 4 ................................................................................................. 37
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23 Top Silkscreen Layer ..................................................................................................... 38
24 Top Copper Layer......................................................................................................... 39
25 Inner Copper Layer........................................................................................................ 39
26 Inner Copper Layer........................................................................................................ 40
27 Bottom Copper Layer ..................................................................................................... 40
28 Drill Drawing................................................................................................................ 41
List of Tables
1 Cell Voltage Connections.................................................................................................. 7
2 USB Interface Connection ................................................................................................. 7
3 JTAG Interface Connection................................................................................................ 8
4 Pack Status Connection.................................................................................................... 8
5 J1, BAT Pin Circuit Configuration......................................................................................... 8
6 J2, VCTL Pin Circuit Configuration ...................................................................................... 8
7 J3, V3P3 Pin Circuit Configuration ....................................................................................... 9
8 J4, V3P3 Pin Capacitor Circuit Configuration ........................................................................... 9
9 J5, SENSEP Pin Circuit Configuration ................................................................................... 9
10 J6, DVCC Pin Circuit Configuration ...................................................................................... 9
11 DIP Switch, S4 .............................................................................................................. 9
12 DIP Switch, S2............................................................................................................. 10
13 Test Points ................................................................................................................. 10
14 Circuit Configuration ...................................................................................................... 12
15 Default Register Values .................................................................................................. 18
16 Formulas to Convert VCOUT to either °C or mV...................................................................... 23
17 Example Log File.......................................................................................................... 26
18 Example of a Device Connect Command.............................................................................. 28
19 Data From MSP430F2122 ............................................................................................... 29
20 Example of a Device Connect Command.............................................................................. 30
21 Bill of Materials............................................................................................................. 37
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Overview www.ti.com
1 Overview
This section describes the features of the bq76925EVM and the equipment that is typically required to
demonstrate and use the EVM.
1.1 Features
A summary of the features of the bq76925EVM follows.
•One bq76925 and one MSP430F2122 device with associated support circuitry
•Support for 3-to 6-series connected cells
–Pluggable terminal block for cell connections, or
–Onboard simulation of cells for operation from a power supply
•bq76925 circuit is jumper configurable for internal or external 3.3-V source
•MSP430 application circuit includes
–JTAG connector
–Reset and SOC buttons
–Four, controllable LEDs
–I2C™interface to bq76925 and to USB-to-GPIO
–Pack status connector
•Supports nominal 4.2-V to 26.4-V pack voltages, 30 V maximum
•20-A continuous charge/discharge current rating
–0.001-Ω(equivalent) shunt resistor
–High-current, stud-type connections for battery power and pack power
•Onboard thermistor for temperature measurement
•Transient voltage protection of PACK±terminals
•Connector for USB-TO-GPIO Adapter
•Test points for monitoring of cell voltages and other important circuit nets
•EVM design files in Mentor Graphics™PADs™2009 format available on request
•Gerber files available on request
1.2 Kit Contents
The bq76925EVM includes the PWR008 printed-circuit board (PCB). Evaluation software is downloadable
from the Texas Instruments Web site (www.ti.com).
1.3 Equipment Requirements
The bq76925EVM includes one PCB containing a bq76925 application circuit. The following equipment
and software are typically needed for operation. Some items depend on the usage case.
1.3.1 bq76925 Evaluation Software
The bq76925 Evaluation Software is the Microsoft™Windows™application that controls and interfaces
with the bq76925. Installation of this software on a compatible personal computer (PC) is required. The
installation file can be found on the product page for the bq76925 on the Texas Instruments Web site.
1.3.2 Microsoft Windows-Compatible Computer
The minimum requirement for the PC and operating system are as follows:
•Pentium™III class or better processor at 1.6 GHz
•Microsoft Windows 2000, XP, or later (32-bit OS)
•512 MB or more RAM
•15 MB of free hard-disk space
•CD-ROM drive
•Adobe™Reader™5.0 or later
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•A color monitor with 1024 ×768 or better resolution
1.3.3 USB-TO-GPIO Adapter
The USB-TO-GPIO Adapter is actually an EVM available from Texas Instruments. It is used to provide the
I2C connection between the bq76925 and the PC.
CAUTION
The USB-TO-GPIO Adapter original firmware is 1.0.10. Firmware version
2.0.19 or later must be installed using the USB-TO-GPIO Firmware Updater
software available (free) on the TI Web site at
http://focus.ti.com/docs/toolsw/folders/print/usb2gpio-loader-sw.html.
1.3.4 Power Supply for Onboard Cell Simulator
A resistor divider network is provided on the bq76925EVM to simulate cells. This allows basic evaluation
of the bq76925 without the use of cells. In this case, a power supply connected between BATT+ and
BATT–is required to power the resistor network. A 24-V power supply with a current capability of 100 mA
is required to power the circuit .
1.3.5 Power Supply for Simulation of Current
A second power supply is used to simulate battery current. The bq76925 expects a sense resistor value of
0.001 Ωand 1 mV is equal to 1 A. A jumper (J5) allows the sense resistor to be disconnected from the
current input of the bq76925 and be replaced with a millivolt source. A power supply that can accurately
provide up to 100 mV can allow for simulated testing of up to 100 A without actually running this
dangerously high current.
1.3.6 Battery
Lithium-ion, rechargeable-type cells can be used with this EVM. Typical cell voltage rating is 3.3 V to 3.7 V
nominal and the pack consists of 3- to 6-series connected cells. Almost all Lithium-ion chemistries can be
used with the bq76925.
WARNING
This EVM has no battery current control devices (MOSFETs) that
can stop the flow of charge or discharge current in the event that a
dangerous condition is induced through discharging or charging
of a battery. Exercise extreme caution when using a battery with
this EVM.
1.3.7 Power Supply to Charge Battery
A power supply can be connected to the PACK±terminals to provide charge current if a battery is
connected to the BATT±inputs.
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WARNING
Use caution when mating batteries with a charger power supply.
Some power supplies cannot tolerate current being fed into their
output terminals. A battery connected to a power supply can easily
cause this to happen. A properly sized blocking diode connected
to the positive output voltage of the power supply can provide
adequate protection against backfeed from the battery and into the
power supply electronics.
1.3.8 Electronic Load
An electronic load is often needed to sink current or power from the battery and through the EVM. A
constant-current load provides a good means of evaluating the performance of the bq76925 when a
battery is used. Equipment rating depends on the application. Typical criteria for electronic load selection
are a voltage rating of up to 4.5 V/cell and up to 20-A discharge capability with 10-mA resolution.
1.3.9 Digital Multimeter
One or two digital multimeters (DMM) capable of voltage, current, and temperature measurement equal to
or greater than the accuracy ratings of the bq76925 are needed for adequate evaluation. Numerous test
clips on the PCB can accept a DMM.
1.3.10 Oscilloscope
An oscilloscope may be needed if evaluation of waveforms or timing measurements is required. Typical
waveforms that a user may be interested in are the I2C signals (100 kHz), cell-balancing waveforms or
capture of the activation time of the ALERT signal after an overcurrent event may be of interest. These
signals can happen down to the 10s of microseconds time base.
2 Circuit Details and Configuration
This section highlights the important features of the EVM circuit, gives some operating instructions, and
also provides a description of the connector pin assignments. Read through this section before using the
EVM for the first time.
CAUTION
Do not connect the battery, power supplies, or interface at this time. Wait until
the next section.
2.1 Connections
Pin 1 on all multisignal-pin headers is indicated by a square solder pad.
2.1.1 BATT+, BATT–(CN1, CN2)
These connections connect the battery terminals to the circuit.
The positive, current-carrying connection of the battery connects to the BATT+ terminal (CN1).
The negative, current-carrying connection of the battery connects to the BATT–terminal (CN2).
The BATT±connections are single, heavy-duty screw terminals that feature a 6-32 ×1/4-in.-long screw.
This connector is rated to 30 A, maximum. Actual current is limited to a lower value (20 A) by other circuit
board components.
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2.1.2 Cells (CN6)
The cell-sensing wires of the battery pack provide the connection for cell voltage measurement and
resistive cell balancing. If the cell count is N, the number of cell wires is N+1.
Table 1. Cell Voltage Connections
Header Name Terminal Label Purpose
1 Cell 6 Cell 6 positive terminal.
2 Cell 5 Cell 5 positive terminal.
3 Cell 4 Cell 4 positive terminal.
CN6 4 Cell 3 Cell 3 positive terminal.
5 Cell 2 Cell 2 positive terminal.
6 Cell 1 Cell 1 positive terminal.
7 Cell 0 Cell 1 negative terminal.
2.1.3 PACK+, PACK–(CN3, CN4)
The positive, current-carrying connection of the load or charger connects to the PACK+ terminal (CN3).
The negative, current-carrying connection of the load or charger connects to the PACK- terminal (CN4).
The PACK±connections are single, heavy-duty screw terminals that feature a 6-32 ×1/4-in. screw. This
connector is rated to 30 A, maximum. Actual current is limited to a lower value (20 A) by other circuit
board components.
2.1.4 USB Interface (CN8)
The USB interface connector (CN8) is for connection to the USB-TO-GPIO Adapter. The pin assignment
is as follows:
Table 2. USB Interface Connection
Header Name Terminal Label Purpose
CN8 1 –V3P3 Monitor and Input
2–ALERT Output
3–None
4–None
5–+3.3V Output
6–Ground
7–None
8–None
9–I2C Clock (SCL)
10 –I2C Data (SDA)
2.1.5 JTAG Interface (CN7)
The JTAG Interface connector (CN7) is for connection to an MSP430 programmer, such as the
MSP-FET430UIF. Use of this connector is not required for evaluation of the bq76925. This header is for
those users who wish to write code for the MSP430F2122 resident on the EVM. The pin assignment is as
follows:
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Table 3. JTAG Interface Connection
Header Name Terminal Label Purpose
CN7 1 1 TDI/TDO
2–VCC-TOOL
3–TDI/VPP
4–VCC-TARGET
5–TMS
6–NONE
7–TCK
8–TEST/VPP
9–GROUND
10 –NONE
11 –RESET
12 –NONE
13 –NONE
14 –NONE
2.1.6 Pack Status (CN5)
The Pack Status header is provided as a convenience for those users desiring to develop firmware for the
MSP430. The default firmware does not use these pins. This connector can be used for GPIO or for an
SPI interface. Total current sourcing from these pins must be limited such that the current rating of the
3.3-V source of the bq76925 circuit is not exceeded. Consult the data sheet for details.
Table 4. Pack Status Connection
Header Name Terminal Label Purpose
CN5 1 GPIO1 GPIO, RXD, SOMI
2 GPIO2 GPIO, TXD(1), SIMO
3 GPIO3 GPIO, SCLK
4 GND Ground
(1) Silkscreen on the board incorrectly reads RXD
2.2 Configuration Jumpers and Switches (J1 –J6, S2, S4)
Two- and three-terminal headers allow the user to configure the operation of the EVM by installing a shunt
at the header. The description of each jumper header is shown in the following tables. Shunts are
provided with the EVM in the default position.
Table 5. J1, BAT Pin Circuit Configuration
Header Name Position Purpose
1 - 2 Zener diode and series diode in BAT pin circuit
(default)
J1 2 - 3 Only series resistor in BAT pin circuit.
Table 6. J2, VCTL Pin Circuit Configuration
Header Name Position Purpose
1 - 2 Internal V3P3 selected. Not recommended when
SOC LEDs are being used.
J2 2 - 3 External V3P3 selected. (default)
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Table 7. J3, V3P3 Pin Circuit Configuration
Header Name Position Purpose
1 - 2 External V3P3 source in circuit (default).
J3 OFF External V3P3 source in circuit
Table 8. J4, V3P3 Pin Capacitor Circuit Configuration
Header Name Position Purpose
1 - 2 External V3P3 source in circuit 1-µF + 4.7-µF
capacitance used (default).
J4 OFF Internal V3P3 source in circuit and 1-µF capacitance
used
Table 9. J5, SENSEP Pin Circuit Configuration
Header Name Position Purpose
1 - 2 SENSEP connected to sense resistor for normal operation
(default).
J5 OFF SENSEP disconnected from sense resistor. This is a test mode
operation where a mV source is applied to J5:pin 1 for simulation
of current.
Table 10. J6, DVCC Pin Circuit Configuration
Header Name Position Purpose
1 - 2 Power to MSP430 during programming is from VCC-Tool. (default)
J6 2 - 3 Power to MSP430 during programming is from VCC-Target.
2.2.1 Cell Simulator DIP Switch (S4)
The eight-position DIP switch (S4) allows the user to simulate cell-voltage inputs to the bq76925 rather
than supply actual cell voltages. See Table 11 for details of the operation of the DIP switch.
CAUTION
Use silkscreen labeling and square pin 1 pad to determine orientation and
operation of the eight-position DIP switch. Ignore numbers actually printed on
the switch.
All S4 dip switches must be opened when using a battery with the EVM.
Table 11. DIP Switch, S4
Switch Terminal Label Purpose
Name
S4 1 Battery Switch to connect power supply to resistor network. Closure
activates LED D13.
2 Cell 6 Applies simulated cell voltage to VC6.
3 Cell 5 Applies simulated cell voltage to VC5.
4 Cell 4 Applies simulated cell voltage to VC4.
5 Cell 3 Applies simulated cell voltage to VC3.
6 Cell 2 Applies simulated cell voltage to VC2.
7 Cell 1 Applies simulated cell voltage to VC1.
8 Cell 0 Applies simulated cell voltage to VC0.
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2.2.2 Circuit Isolation DIP Switch (S2)
The eight-position DIP switch (S2) allows the user to isolate the MSP430 circuit from the bq76925 circuit.
Circuit isolation may be needed to measure some performance characteristics of the bq76925 or during
MSP430 programming.
CAUTION
Use silkscreen labeling and square pin 1 pad to determine orientation and
operation of the eight-position DIP switch. Ignore numbers actually printed on
the switch.
Table 12. DIP Switch, S2
Switch Name Terminal Label Purpose
S2 1 V3P3 Controls application of V3P3 from bq76925 to MSP430
2 Therm Isolates the THERM circuit when opened.
3 VCOUT Isolates the VCOUT circuit when opened.
4 VIOUT Isolates the VIOUT circuit when opened.
5 SDA Isolates the SDA circuit when opened.
6 SCL Isolates the SCL circuit when opened.
7 ALERT Isolates the ALERT circuit when opened.
8 VRef Isolates the VREF circuit when opened.
2.3 Pushbuttons (S1, S3)
The two pushbuttons on the EVM are normally open, momentary-style buttons. The pushbutton labeled
RESET (S1) is the reset button for the MSP430. Pressing this button restarts the MSP430.
The pushbutton labeled LEDs (S3) is intended to be a display control for the state of charge (SOC) display
formed by the four LEDs (D8 –D11). Pressing this button triggers an input on the MSP430 that
incrementally lights the four LEDs –despite what the actual SOC of the battery may be that is connected
to the EVM. This is the default functionality defined by the firmware. The user can choose to use the
pushbutton in another way by creating new firmware for the MSP430.
2.4 Test Points
Twenty-nine test loops are located on the EVM. Table 13 names the circuit connected to each test point.
The first 20 test points correspond one-to-one to the pin number on the bq76925.
Table 13. Test Points
Label Ground Reference Test Point
TP1 VCTL
TP2 BAT
TP3 VC6
TP4 VC5
TP5 VC4
TP6 VC3
TP7 VC2
TP8 VC1
TP9 VC0
TP10 VSS
TP11 SENSEN
TP12 SENSEP
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Table 13. Test Points (continued)
Label Ground Reference Test Point
TP13 ALERT
TP14 VIOUT
TP15 VCOUT
TP16 VTB
TP17 VREF
TP18 SDA
TP19 SCL
TP20 V3P3
TP21 BATT+
TP22 PACK–
TP23 P2.5 ON MSP430
TP24 P3.7 ON MSP430
TP25 P3.5 ON MSP430
TP26 P3.4 ON MSP430
TP27 P3.0 ON MSP430
TP28 VSS
TP29 VSS
2.5 bq76925
The bq76925 application circuit provided allows for complete evaluation of the device performance with 3-,
4-, 5-, or 6-cell battery packs. Cell voltages, battery current, and temperature can be monitored.
Monitoring is possible with the firmware that is preloaded into the MSP430 microcontroller and with the
bq76925 Evaluation Software provided. Alternatively, the user can develop a custom system if desired.
2.6 MSP430F2122
The MSP430F2122 application circuit is provided to read the analog signals from the bq76925 and make
them available for reading over the I2C bus by the bq76925 Evaluation Software. The MSP430 circuitry is
designed to allow the user to create custom firmware if desired.
3 Quick-Start Demonstration
This section demonstrates the measurement system of the bq76925 using the onboard cell simulator.
To quickly get the bq76925EVM up and running, follow the instructions in this section. The following
equipment and software are required:
•bq76925EVM Evaluation Module
•A 24-Vdc power supply
•Power supply capable of up to 100 mV and at least 100 mA of drive capability.
•PC with MS Windows operating system
•bq76925 Evaluation Software
•USB-TO-GPIO Adapter
3.1 Evaluation Software and USB-TO-GPIO Adapter
The bq76925 Evaluation Software and the USB-TO-GPIO Adapter must be installed and set up.
The USB-TO-GPIO Adapter is an EVM that is sold separately from the bq76925EVM. The firmware in it
must be changed to work with the bq76925 because this EVM was developed for generic applications. Go
to the TI Web site to download the firmware loader.
http://focus.ti.com/docs/toolsw/folders/print/usb2gpio-loader-sw.html
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With the USB-TO-GPIO Adapter connected to the PC, follow the instructions included with the firmware
loader software, and change the firmware version to 2.0.19. All necessary files are included with the
USB-TO-GPIO Firmware Updater.
CAUTION
If the firmware download fails, do not disconnect the USB-TO-GPIO Adapter.
Try to load the firmware again until it is successful. Removing power after a
failed download can permanently damage the USB-TO-GPIO Adapter.
The bq76925 Evaluation Software is free to download from the product page for the bq76925 on the TI
Web site. Follow the installation instructions in the install package.
3.2 Configuration Switches and Jumpers
Before applying any power to the board, ensure that all of the jumpers and switches are set up correctly
for this demonstration. A summary of all of the jumper and switch positions appears in Table 14.
Table 14. Circuit Configuration
Header Shunt or Switch Notes
Name Position
J1 1 –2 Zener and blocking diode on BAT Pin
J2 2 –3 External Pass Transistor enabled
J3 ON External Pass Transistor enabled
J4 ON 5.7- µF capacitance on V3P3 pin.
J5 ON Normal mode
J6 1 –2 VCC from Tool
S2 ON All eight switches to the closed position.
S4 ON All eight switches to the closed position.
3.3 Power to the bq76925EVM
Ensure that the configuration described in Table 14 has been verified.
The bq76925EVM must be powered from a power supply for this demonstration. The power supply drives
an onboard cell simulator as well as powers the bq76925 and MSP430 circuitry. No battery is required at
this point.
Connect a 24-V power supply with current drive of at least 100 mA between the BATT+ and BATT–. Turn
on the output of the power supply.
On application of power, the red LED, D13, illuminates.
A voltmeter can be used to verify that the 3.3-V output is working. Place the voltmeter between test points
TP20 and TP10.
3.4 Connect USB-TO-GPIO Adapter
Connect the USB cable provided with the USB-TO-GPIO Adapter between the PC with the Evaluation
Software installed on it and the USB-TO-GPIO Adapter.
The green LED near the USB connector illuminates to indicate that the USB-TO-GPIO Adapter is properly
connected. Because of the marginal mechanical design of the case, the USB connection can sometimes
become intermittent. The green LED is a good indication if a connection problem exists.
Connect the ribbon cable provided with the USB-TO-GPIO Adapter from it to header CN8 on the
bq76925EVM. The red LED, D12, illuminates.
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3.5 bq76925 Evaluation Software
3.5.1 Open the Application
Having followed the instructions in the previous sections, open the bq76925 Evaluation Software.
The following screen appears (Figure 1). This main screen is often referred to as the home screen.
Figure 1. Home Screen of the Evaluation Software
3.5.2 Start Polling Data
Data from the bq76925 can be polled and displayed in the application. To start polling, click on the Poll
button.
Figure 2. Poll Button in the Evaluation Software.
With polling active, the cell voltages and temperatures update on a periodic basis. The poll indicator light
next to the word POLL flashes between green and orange for each poll cycle.
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Figure 3. Poll Button in the Evaluation Software
3.5.3 Add Second Power Supply to Simulate Current
One way to easily simulate battery current is to apply a millivolt source to the current-sense inputs of the
bq76925. Tens of amperes can be simulated where each 10 mV is equal to 10 amperes.
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+-
24.0V 100mA
Power Supply1
50mV 100mA
Power Supply2
- +
Personal Computer
Windows XP32 Bit
with
bq76925 Evaluation
Software Installed
USB
USB-TO-
GPIO
Adapter
www.ti.com Quick-Start Demonstration
Figure 4. Demo With Two Power Supplies
Remove the shunt from header J5. Use the second power supply to apply 50 mV between pin 1 of header
J5 and the BATT- terminal. This simulates approximately –50 A or –50,000 mA, of discharge current.
Figure 5. Voltage, Temperature, and Current Measurement in the Evaluation Software
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The drop-down box labeled Select Cell Count determines the number of cell voltage measurements that
are displayed: 1 to 6. This function is independent of the cell count. For example, if the user only wanted
to display 3 cells of a 6-cell pack, then the Select Cell Count box is changed to 3. This convenience
feature avoids seeing a somewhat random number being displayed for unconnected cell inputs.
Figure 6. Select Cell Count Set to Three Cells
4 Control Register Demonstration
The Quick-Start demonstration from the previous section presents the fundamental measurement system
of the bq76925. The method to access and modify the Control Registers using the Evaluation Software is
presented in this section.
4.1 View Control Registers
4.1.1 Introduction
Open the Evaluation Software, if not already open, and click the checkbox marked Show Volatile Control
Registers.
Figure 7. Volatile Control Registers Checkbox
This expands the home window to show the six registers.
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Figure 8. Volatile Control Registers Access
All of the bits that are assigned for reading and writing are shown. Bit positions that are unnamed are not
used. These bits must always be left as zero.
A legend that can be clicked explains the bit colors. A zero value for a bit is displayed as a grey
background. A one is shown as either a green background or as an orange background.
Clicking each bit toggles the bit value in real time. If a bit turns green, it is set to a 1. If a bit is white or
grey, it is a zero. Each of the STATUS bits is displayed in orange when they are a value of 1.
If the SLEEP bit is a 1, it halts communications, so that the status of this bit is unable to be displayed. The
SLEEP bit always appears to be OFF or MASKED.
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Figure 9. Volatile Control Registers Bit Legend
4.1.2 Factory-Programmed Register Values
The Control Registers are programmed at the factory to have a default value. Table 15 shows these
values.
Table 15. Default Register Values
Address Register Default Value
0x00 STATUS 0x01
0x01 CELL_CTL 0x10
0x02 BAL_CTL 0x00
0x03 CONFIG_1 0x00
0x04 CONFIG_2 0x81
0x05 PWR_CTL 0x00
4.1.3 Register Values When Polling
When the Polling button is pressed, the PWR_CTL register is forced to the value of 0x1F. This turns on all
measurement systems as well as the current comparator. This is shown in the Control Register Display.
Note that other bits are automatically updated (written) during polling but are not displayed (read). The
update rate of the bits during polling is in the 10s of milliseconds and does not make sense to display.
4.2 Control Registers Introduction
The Control Registers of the bq76925 are used to configure and control the device. A summary of the
read/write Control Registers follows. This user's guide, however, does not provide the necessary details
on the operation and settings of these registers that are given in the bq76925 data sheet . For those
details, see SLUSAM9.
Mousing over a bit in the Control Register section of the software displays a brief description of the bit.
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4.2.1 STATUS: 0x00
Bit 0 is the Power On Reset Flag (POR). It is set on a each power-up and wake up from sleep.
Bit 1 is the CRC Error Status Flag (CRC_ERROR). It is updated on every I2C write packet.
Bit 2 is the Overcurrent Alert Status Flag (ALERT). This reflects the state of the overcurrent comparator.
4.2.2 CELL_CTL: 0x01
Bits 0-2 are the cell select bits (CELL_SEL) that determine which cell voltage input (VC1 –VC6) is sent to
the VCOUT pin.
Bits 4-5 are the VCOUT multiplexer selector bits (VCOUT_SEL). These bits determine the output of the
VCOUT pin: either VSS, VCn, Vref x 0.5, or Vref x 0.85.
4.2.3 BAL_CTL: 0x02
Bits 0-5 are for cell balance control (BAL_1…BAL_6).
4.2.4 CONFIG_1: 0x03
Bit 0 is the current amplifier gain select bit (I_GAIN). The gain can be set to 4 or 8.
Bit 2 is the current amplifier calibration bit (I_AMP_CAL). It is used to select the current measurement:
from SENSEN or SENSEP.
Bit 3 is the current comparator polarity select bit (I_COMP_POL). This determines the current direction
used to trip the comparator: charge or discharge.
Bits 4 –7 determine the current comparator threshold setting (I_THRESH). Sixteen different mV levels are
available.
4.2.5 CONFIG_2: 0x04
Bit 0 is used to set the reference voltage level (REF_SEL). VREF has two different voltage levels.
Bit 7 is used to enable or disable the I2C CRC.
4.2.6 POWER_CTL: 0x05
Bit 0 is used to enable or disable the reference voltage (REF_EN).
Bit 1 is used to enable or disable the thermistors bias voltage (VTB_EN).
Bit 2 is used to enable or disable the cell voltage amplifier (VC_AMP_EN).
Bit 3 is used to enable or disable the current amplifier (I_AMP_EN).
Bit 4 is used to enable or disable the current comparator (ICOMP_EN).
Bit 6 is used to disable the sleep mode (SLEEP_DIS).
Bit 7 is used to enter sleep mode (SLEEP).
4.3 Modifying Control Registers
Control register bits that are writable can be modified by simply clicking on the bit that the user wishes to
change. The modification is immediately communicated by the Evaluation Software to the bq76925.
4.4 Sleep Mode and Wake Up
The bq76925 can be put into a low-power mode called Sleep. Bit 7 in the PWR_CTL register is called
SLEEP. When this bit is set to a 1, the part shuts down the V3P3 output and enters the low-power state.
To enter sleep mode, simply click the SLEEP bit in the Control Registers display.
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The bq76925 shuts down the 3.3-V level at the V3P3 pin. The Hardware IO section shows a red light next
to V3P3 to indicate that the 3.3-V level is now zero. The Evaluation Software actually monitors the V3P3
output of the bq76925 via the USB-TO-GPIO Adapter input on pin 1.
Figure 10. Sleep Mode Showing 3.3-V Status
The method to wake the part from sleep is to apply a voltage, 3.3 V in the case of the bq76925EVM, to
the ALERT pin. This is accomplished easily by clicking the Wake button in the Hardware IO Section.
Figure 11. Wake Up From Sleep Mode
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