Texas Instruments BQ76905 User manual

EVM User's Guide: BQ76905EVM
BQ76905 Evaluation Module
Description
The Texas Instruments' BQ76905EVM is a complete
evaluation system for the BQ76905, The BQ76905 is
a highly integrated, high accuracy battery monitor and
protector for 2-series to 5-series Li-Ion, LiPolymer,
and LiFePO4 battery packs.
The circuit module connects directly to the cells in
a battery, or can be connected with a power supply
and the included cell simulator resistors. With the on-
board interface or compatible external interface board
and Microsoft® Windows® based PC graphical user
interface (GUI) software, the user can view the device
registers, evaluate voltage, current and temperature
accuracy, adjust protection limits and enable FET
control outputs.
Get Started
1. Order the BQ76905 EVM from ti.com.
2. Download the latest BQSTUDIO-TEST from the
BQSTUDIO tool page.
3. Follow the instructions in this user's guide to get
started.
Features
• Complete evaluation system for the BQ76905 2-
cell to 5-cell Li-Ion, LiPolymer, and LiFePO4 high
accuracy battery monitor
• Power connections available on test points
• Communication available with included USB
interface adapter or available on 4-pin connector
• Resistor cell simulator for quick setup with only a
power supply
• PC software available for configuration
Applications
•Cordless power tools and garden tools
•Vacuum cleaners
•Non-military drones
•Other industrial battery pack (2-series to 5-series)
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1 Evaluation Module Overview
1.1 Introduction
The BQ76905 features a high accuracy monitoring system with dedicated coulomb counter and accumulated
charge integration, a highly configurable protection subsystem, and support for host controlled cell balancing.
Integration includes low-side protection NFET drivers, a programmable LDO for external system use, and an
I2C host communication interface supporting up to 400-kHz operation with optional CRC. The evaluation module
includes one BQ76905 integrated circuit (IC), sense resistor, one thermistor, power FETs, and all other onboard
components necessary to protect the cells from overcharge, over discharge, short circuit, overcurrent discharge,
over temperature, and under temperature.
1.2 Kit Contents
• BQ76905 circuit module
• USB A to microUSB cable
1.3 Specification
This section summarizes the performance specifications of the BQ76905 circuit module in the default 5-cell
series FET configuration.
Typical voltage depends on the number of cells configured. Typical current depends on the application. Board
cooling can be required for continuous operation at or below maximum current.
Table 1-1. Performance Specification Summary
Specification Min Typ Max Unit
Input voltage BATT+ with respect to BATT– 3 – 25 V
Continuous charge or discharge current 0 – 6 A
Operating temperature range 20 25 30 °C
1.4 Device Information
Table 1-2. Device Information
EVM Part Number Chemistry Configuration Capacity
BQ76905EVM Li-Ion 5 cells Any
Note
Although capacity is shown as Any, practical limits of the physical construction of the module typically
limits the operation of the EVM to a 1P or 2P battery construction. Refer to the physical construction
section for board details.
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2 Hardware
2.1 Before You Begin
The following warnings and cautions are noted for the safety of anyone using or working close to the BQ76905
EVM. Observe all safety precautions.
Warning
The BQ76905EVM circuit module can become hot during operation due to
dissipation of heat. Avoid contact with the board. Follow all applicable safety
procedures applicable to your laboratory.
!
Caution Do not leave the EVM powered when unattended.
CAUTION
The default settings of the BQ76905 do not limit performance to the ratings of the EVM. Set all
protections appropriately and limit current for safe operation.
CAUTION
The circuit module has signal traces, components, and component leads on the bottom of the board,
which can result in exposed voltages, hot surfaces or sharp edges. Do not reach under the board
during operation.
CAUTION
The circuit module can be damaged by over temperature. To avoid damage, monitor the temperature
during evaluation and provide cooling, as needed, for your system environment. Do not operate
beyond the current and voltage limits in the Specification Table.
CAUTION
Some power supplies can be damaged by application of external voltages. If using more than
1 power supply, check your equipment requirements and use blocking diodes or other isolation
techniques, as needed, to prevent damage to your equipment.
CAUTION
The communication interface is not isolated on the EVM. Be sure no ground potential difference
exists between the computer and the EVM. Also, be aware that the computer is referenced to the
battery-potential of the EVM.
CAUTION
Connections for rated current must be made at the terminal block. Test points are not rated for the
board current.
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2.2 Required Equipment
The following equipment is required to operate the BQ76905 EVM in a simple demonstration:
• DC power supply, 0–35 V at 2.5 A
• DC voltmeter
• Computer with USB port and compatible Windows operating system and access to the internet
• Test leads to connect equipment
• Electronic load or assorted resistors
Additional equipment can be desired to operate the BQ76905 with a more extensive demonstration.
2.3 BQ76905 Circuit Module Use
The BQ76905 circuit module contains the BQ76905 IC and related circuitry to demonstrate the features of the
IC. Surface mount FETs are provided for the high current path. A thermistor provides temperature sensing on the
board. Other components provide support for the IC and connections to the board. Basic operation is described
in Section 3. For details of the circuit, refer to Section 5.
2.3.1 Cell Simulator
The EVM includes a resistive cell simulator made up of 200-Ω series resistors. The taps of the resistor network
are connected to the cell inputs using shunts on the J10 header. BAT- is always connected to the resistor divider
network. Installing a shunt on the top cell location connects the top cell input to the resistor divider to provide
simulated voltages for the other cell inputs. If the shunt is not installed on the top cell position of the header,
then all lower inputs are pulled to VSS. Installing shunts for the lower cell positions connects the input to the
simulated voltage. Since here is no indication of the cell simulator connection, the user must be aware of the
shunt installation.
2.3.2 Evaluating with Load Current
With the BQ76905 configured and the FETs enabled, discharge current can be demonstrated by attaching
appropriate resistors or a DC load at the PACK terminals as shown in Figure 2-1.
DC Power Supply
+ -
Install cell
simulator shunts
DC Load + -
Figure 2-1. Evaluating with Load Current
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2.3.3 Evaluating Charge and Discharge Currents
Bipolar power supplies source or sink currents to maintain the set voltage. When bipolar supplies are available,
the bipolar supplies can be used for both the battery and pack side of the board to allow charge and discharge
currents without re-connecting the equipment. Be sure to set the supplies appropriately to prevent exceeding the
ratings of the EVM.
Bipolar DC Power Supply
(source/sink)
+ -
Install cell
simulator shunts
Bipolar DC Power Supply
(source/sink) + -
Figure 2-2. Evaluating with Charge or Discharge Current
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2.3.4 Evaluating with Simulated Current
Section 3 describes connection for basic operation. Providing more than recognizable current in that
configuration can require a power supply with a significant power rating. Applying a charge current can damage
some power supplies. Figure 2-3 shows a method to force current through the control path without a high
wattage power supply or special equipment. The load power supply must be set at a low voltage in a constant
current mode. Polarity can be reversed on the load supply to simulate a charge current. The battery simulation
supply must never be reversed.
DC Power Supply
+ -
Install cell
simulator shunts DC Power Supply
(Simulated load) +
-
Figure 2-3. Simulating Current Setup
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2.3.5 Reducing the Cell Count
The BQ76905 must have the top and bottom cells used for proper operation. Cell count can be reduced by
shorting the unused cell inputs from the next-to-top down. Cell count can be reduced for basic evaluation by
shorting unused cells at the input terminal block. Follow the recommendations in the data sheet for which cells to
short. This works for both operation with the cell simulator and cells, but can have some side effects in transient
tests because the shorted resistors are parallel to the cell IC where the capacitor provides a signal path to
the used input. See Figure 2-4 for an example of simple reduced cell configuration for 3 cells. For the best
evaluation with reduced cells in a transient environment, short the VCx pins at the capacitor and remove the
unused input resistor. When using the cell simulator, shorting the unused cell at the terminal block is still required
to eliminate the simulated cell voltage. Shorting the cell inputs at the terminal block screw terminals is suggested
since the cell inputs are apparent if the board is re-used for a different cell count. Table 2-1 shows configuration
recommendations for reduced cell count, this table assumes the board has been set-up as detailed in Section 3.
By default, the BQ76905 EVM has VC4A/B and VC3A/B shorted at the IC inputs. However, the user
must make sure to also short CELL6 to CELL5 and CELL4 to CELL3 on the cell input terminals prior
to making any cell reduction, as explained in Section 3.
Table 2-1. Reducing Cell Count
Unused cell
(numbered from bottom
cell 1)
Short cell input
terminals
Input resistor to
remove
Replace capacitor with
0 ohm IC inputs shorted
Cell 4 CELL5 to CELL4 R8 C7 VC4A/B to VC3A/B
Cell 3 CELL3 to CELL2 R11 C9 VC3A/B to VC2
DC Power Supply
+ -
Install cell
simulator shunts
Short
CELL6 all the way
down to CELL2
Figure 2-4. Example 3 Cell Simple Evaluation Configuration
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2.3.6 Connecting Cells
The EVM is constructed with a single connection to the top and bottom of the cell stack. Cell voltage for these
cells is sensed on the board.
The cell simulator provides resistors between the cell inputs. When the cell simulator shunts are installed, these
resistors load the cells and divide the voltage to any unconnected inputs as cells are connected. If desired, then
the cell simulator shunts can be installed during cell connection and removed after cell connection. The shunts
must be removed after connection of cells or the cells are discharged by the constant drain of the cell simulator
resistors.
BAT- is the reference voltage for the IC and must be connected first. After BAT- cells can be connected in any
order. Cell connection from the bottom up minimizes the voltage step size applied to the board. Recommended
connection sequence for the EVM when connecting cells is bottom up:
1. Connect BAT–
2. Connect cells bottom up: CELL1, CELL2, CELL3 ...
3. Be sure the cell simulator shunts are removed
Figure 2-5 shows an example connecting cells with an EVM configuration reduced to 4 cells.
Remove cell
simulator shunts to
avoid draining cells
If connecting cells confirm operation before connecting.
Use all appropriate fusing, insulation, isolation and
shielding necessary for safe operation. Board has exposed
contacts. Do not leave unattended
For 4 cells, connect 3th
cell to CELL6 to CELL3
inputs
Figure 2-5. Example Connection with 4 Cells
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2.3.7 Connecting to a Host
After initial operation of the monitor with the BQStudio software, consider operating the board connected to and
controlled by a microcontroller board. To do this, unpopulate J6 and J2, and populate J1 and J5. J6 and J2
disconnect the I2C lines of the BQ76905 from the on-board MCU. J1 and J5 connect the I2C pullup resistors to
REGOUT.
DC Power Supply
+ -
Install cell
simulator shunts
Add shunts for
pull-ups if pull-
ups not provided
on MCU board
MCU
Evaluation Board
SCL
Remove shunts
for on-board MCU
connection
SDA
Figure 2-6. Host Connection Concept
2.3.8 Hardware Configuration
2.3.8.1 Configuration Jumpers
Certain features on the BQ76905EVM can be configured by jumpers or shunts on headers. See Section 5.1 for
details of the header pins.
J1 and J5 connect the BQ76905 I2C lines to pull-up resistors at REGOUT for off-board MCU communications.
J2 and J6 connect the I2C lines of the BQ76905 to the on-board MCU.
J7 connects the ALERT pin to a pull-up resistor at REGOUT.
J8 connects/disconnects the on-board thermistor from the TS pin.
J10 cell simulator connections.
The cell simulator headers and are discussed in board connection diagrams.
2.3.9 Configuration Register Programming
Configuration register programming is done once hardware configuration is set with jumpers. Configuration
registers are set in the Data Memory screen and are different from the status registers displayed in the Registers
screen. See the BQ76905 data sheet (SLUSF45) and supporting documentation for register information. When
a configuration file is available, the file can be imported to set all operational selections at once. However, a
configuration file loaded with Data Memory Import can load as little as 1 parameter, so the user must be familiar
with the contents of imported files. With a new device or after loading a configuration file, individual register
changes can be made. Configuration register programming typically involves the following general principles
selected in various register names:
1. Selection of the protection features to be enabled
2. Selection of the protection thresholds for the enabled features
3. Setting the FET control options
4. Exporting (saving) the configuration register file for future use
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3 Quick Start Guide
The BQ76905 registers must be configured to enable most protections, select the monitored cells, and enable
the protection FETs on the EVM. This section does not describe current protection settings.
These steps describe quick connection of the BQ76905 EVM to demonstrate operation of the AFE portion of the
EVM. For more detailed descriptions, refer to other sections of the user's guide.
Refer to Figure 3-1 for the following steps.
1. Download the BQSTUDIO software from the tool folder link www.ti.com/tool/BQSTUDIO or search from
www.ti.com.
2. Install the BQStudio software (see Section 4.1.2).
3. Install the cell simulator shunts.
4. VC4A to VC4B and VC3A to VC3B are shorted directly at the pins. However, CELL6 to CELL 5 and CELL4
to CELL 3 must also be shorted at the cell-side for proper circuit module functionality.
5. Position shunts for the I2C to MCU connection.
6. Attach the on-board communication adapter USB connector to the PC using USB cable.
7. Connect a 0-V DC power supply capable of 250 mA minimum between the “BAT-” and "7P" terminals and
adjust to approximately 15 V.
8. Start the BQStudio software. If there is proper communication, then the GUI opens with a register display.
Click on the Scan button to enable repeated update of the display. The power supply can be adjusted within
range of the part to observe voltage changes in the GUI register display.
9. Select the Data Memory button in the BQStudio window.
10. Select the Settings button. Set the Enabled Protections A CUV bit.
11. Select the Protections button. Set the Cell Undervoltage Protection Threshold to 2800.
12. In the Commands panel click on the FET_ENABLE button.
13. In the Registers view click on the Scan icon so that the registers update periodically. Observe that the CHG
and DSG bits in the Battery Status register are on. Measure the PACK voltage on the board if desired.
14. Adjust the supply voltage to approximately 12.5 V. In the registers view observe that the DSG bit goes off.
15. Make other adjustments as desired for evaluation. See other sections of this user guide for details of
operation.
16. When complete with this quick start demonstration, exit the BQStudio software and turn off the power supply.
Refer to other sections of this user's guide for additional details.
Short
CELL6 to CELL5 and
CELL4 to CELL3
DC Power Supply
+ -
Install cell
simulator shunts
Position shunts
to uC_SCL and
uC_SDA
Figure 3-1. EVM Connection for Basic Operation
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