Texas Instruments bq77905 User manual

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bq77905 3-5S Low Power Protector Evaluation Module
User's Guide
SLVUAN2A–May 2016–Revised July 2016
bq77905 3-5S Low Power Protector Evaluation Module
This evaluation module (EVM) is a complete evaluation system for the bq77905 3-5S low power protector
for lithium-ion cells. The EVM includes one bq77905 and FETs to control current in a configuration typical
for switching current in a lithium-ion battery pack. The circuit module includes one bq77905 integrated
circuit (IC), a sense resistor, thermistor, two CSD18534Q5A FETs, and all other onboard components
necessary to switch charge and discharge current. The circuit module connects between a "battery"
source and a "pack" load. In addition to the current and voltage applied to the module the user can
remove on-board jumpers to simulate over- or under-temperature conditions to observe FET control under
different charge and discharge conditions.
1 Features
• Complete evaluation system for the bq77905 3-5S Low Power Protector IC
• Populated circuit module for quick setup
1.1 Kit Contents
• bq77905 circuit module
1.2 Ordering Information
The EVM orderable part number is bq77905EVM-707. For complete ordering information, see the product
page at www.ti.com.
1.3 Documentation
See the device data sheet for bq77905 (SLUSCM3)onwww.ti.com for information on device hardware.
1.4 bq77905 Circuit Module Performance Specification Summary
This section summarizes the performance specifications of the bq77905EVM.
Table 1. Performance Specification Summary
Specification Minimum Typical Maximum Unit
Input voltage BATT+ to BATT– 3 18 25 V
Output voltage PACK+ to PACK- 0 18 25 V
Charge and discharge current 0 2 3 A
Operating temperature 20 25 30 oC
While the board is rated at 3A, this is the nominal over current limit of the installed bq77905 configuration.
Other components may have a higher rating.

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2 bq77905EVM Quick Start Guide
This section provides the step-by-step procedures required to use a new EVM and configure it for
operation in a laboratory environment.
2.1 Before You Begin
The following warnings and cautions are noted for the safety of anyone using or working close to the
bq77905 EVM. Observe all safety precautions.
CAUTION
The circuit module has signal traces and component leads on the bottom of the
board. This may result in exposed voltages, hot surfaces, or sharp edges. Do
not reach under the board during operation. Do not operate the EVM on a
conductive surface.
CAUTION
The circuit module may be damaged by overtemperature. To avoid damage,
monitor the temperature during evaluation and provide cooling, as needed, for
your system environment.
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.
CAUTION
The circuit module is not a finished product or electrical appliance. It must be
used by qualified personnel with additional equipment for evaluation only. Do
not leave EVM powered when unattended.
2.2 Items Needed for EVM Quick Start Evaluation
• A bq77905 circuit module
• An adjustable DC power supply that can provide 10 V to 23 V and 1 A minimum (a voltage range,
bipolar operation, and constant current – constant voltage capability is desirable)
• Five resistors for cell voltage simulation such as 200 Ω1% 1/4-W or other suitable value
• A load such as a 5-kΩ, 1/4-W or other suitable resistor
• A DC meter or measurement instrument
• Some suitable cables for connection
2.3 EVM Connections
This section covers the hardware connections for the EVM (see Figure 1).

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Figure 1. bq77905 Circuit Module Connection for Simple Demonstration
• Supply terminal block (J2)
These are the supply terminals for the board. BATT+ or CELL5 is the positive terminal of the power
supply and BATT– is the negative terminal of the power supply. The inputs CELL1 through CELL4 are
divided between the BATT+ and BATT- voltages. When using a power supply for evaluation, be sure
the power supply can accept or is protected from any reverse current such as with a blocking diode if
another supply is used in the system.
• Pack terminals (J6)
PACK+ and PACK– terminals are for attachment for the load or charger. If using a power supply to
simulate a charger, be sure it can accept or is protected from any reverse current.
• "H" shunt (J3)
This shunt shorts J3 pins 1 and 2 connecting the IC VTB pin to the temperature measurement path. A
hot temperature is simulated when the shunt is removed.
• "L" shunt (J3)
This shunt shorts J3 pins 3 and 4 connecting the IC TS pin to the thermistor. A cold temperature is
simulated when the shunt is removed.
2.4 Quick Start Sequence
These steps describe a simple demonstration or check of the operation of the bq77905EVM in a 5S
configuration with a typical 18-V stack voltage.
1. Connect 5 200-Ωresistors between the cell terminals of J2.
2. Confirm the "H" and "L" shunts are in place on J3.
3. Connect an 18-V adjustable DC power supply across the BATT+ and BATT– terminals of J2.
4. Enable the supply.
5. Measure the voltage on the pack terminals. Observe that this is the same voltage as the supply
because both charge and discharge FETs are on, approximately 18 V.
6. Connect a load such as a 5-kΩresistor across the PACK terminals
7. Adjust the supply voltage to 23 V to simulate an overvoltage condition. Observe that the voltage on the
PACK terminals is approximately 600 mV below the supply voltage because the charge FET is off.
8. Adjust the supply voltage to 18 V to cause recovery from the overvoltage condition. Observe that the
voltage on the PACK terminals is the supply voltage.
9. Remove the shunt at the J3 H position to simulate a hot condition. Observe that the pack voltage drops
to approximately 0 V, and returns to normal when the shunt is re-installed.

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10. Remove the shunt at the J3 C position to simulate a cold condition. Observe that the pack voltage
drops to approximately 0 V and returns to normal when the shunt is re-installed.
11. Adjust the supply voltage to 12 V to simulate an undervoltage condition. Observe that the pack voltage
drops to approximately 0 V.
12. Adjust the supply voltage to 18 V to allow recovery from the undervoltage condition. Observe that the
pack voltage remains at approximately 0 V with the load resistor in place.
13. Remove the load resistor on the PACK terminals. Observe that the pack voltage returns to the supply
voltage because undervoltage recovers on the installed part configuration with both voltage and load
removal.
14. Disable the power supply and disconnect, if complete.

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supply
(2 quadrant)
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(2 quadrant)
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3 Additional Evaluation Setups
CAUTION
The bq77905 EVM does not contain capacitors on the input or output current
paths to dampen transients. Be sure to use appropriate transient suppression
to avoid damage to the board from cable or equipment transient responses
during evaluation.
3.1 Operation With Charge and Discharge Currents
If bipolar power supplies are available, current control can be demonstrated through the board in both
directions, see Figure 2. A battery voltage in range must be applied to the BATT side of the EVM for
operation. The instrument on the PACK side can be used as a load if it is set to a lower voltage than the
battery side or as a charger if set to a higher voltage. Additional equipment can be used to adjust the
voltage across the individual input resistors to simulate different cell voltages.
Figure 2. Bipolar Operation
Operation can also be demonstrated with conventional supplies and loads. Connect and operate the
equipment within its performance limits.
3.2 Reducing the Cell Count
The bq77905 EVM may be modified to provide monitoring of three or four cells. A concept of simple three-
cell evaluation is shown in Figure 3. Cells are connected from the bottom up with unused top cell inputs
connected to the top cell at J2. While this is not the direct IC pin connection shown in the datasheet, it will
work for general evaluation. The CCFG pin must also be connected to AVDD or GND to select monitoring
of three or four cells. This can be done by adding a jumper at the J4 pattern between pins 1 and 2 or 2
and 3 as desired. The board is marked with "4" next to pin 1 and "3" next to pin 3. If the board will be used
for further evaluation be sure to remove the jumper at J4 after the reduced cell test.
CAUTION
With a jumper installed at the J4 pattern the bq77905 will not evaluate the top
one or two cells depending on the jumper installation. Remove any jumper to
monitor all cell inputs.

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supply
+ -
Add jumper
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Figure 3. Operation with Reduced Cell Count
3.3 Connecting to Cells
It is recommended that the user operate the bq77905 EVM with power supplies to become familiar with
the operation and features of module and bq77905 before connecting cells. The bq77905 EVM may be
connected to cells so that the cells can provide the power for the bq77905, a concept is shown in
Figure 4. The cells should be connected together before connecting to the board. The BATT- connection
should be made first, then other cell connections can be made in any sequence.
Figure 4. Connecting to cells

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supply
RLOAD
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Modify components
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3.4 Stacking Modules
While the bq77905 EVM modules do not stack as delivered, they can be modified for a basic
demonstration of stacking by adding additional components. The resulting circuit is not ideal because the
ESD capacitors will remain across each module rather than across the pack terminals. The charge and
discharge FETs installed are 60-V rated and will normally accommodate connection of two EVMs.
Connection of more than two EVMs is not supported by the patterns on the board and is not
recommended. Before connecting the modules, the bottom module must have component additions and
changes shown in Table 2 to enable the stacking inputs and support the UV load removal recovery
detection for the upper device. A connection example of the two modules is shown in Figure 5.
Table 2. Bottom Module Modifications for Stacking
Reference Designator Action Function
R2 Install 10-MΩresistor
Stacking interface
R3 Install 10-MΩresistor
R6 Remove
R7 Remove
R20 Install 470-kΩresistor UV Load Detect Recovery
D3 Install BAS16J switching diode
Figure 5. Stacking Circuit Modules

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CAUTION
The bottom bq77905 module will not receive fault conditions from the top
module unless properly modified and connected. Confirm operation of your
modified evaluation setup.
Once modified, the bottom module will not enable FETs when disconnected from the top module.
3.5 Troubleshooting
If the bq77905 does not appear to be operating, check the VDD voltage at TP1 as this should be the
same as the BATT+ voltage. Check the AVDD voltage at J4 pin 1, this should be approximately 2.5 V.
Check that the shunts are installed at the H and L positions on J3 shorting pins 1 to 2 and pins 3 to 4.
Check that the cell input voltages are within the operating range of the part. If a fault has been induced,
check that the recovery condition has been met. The configuration of the supplied IC requires load
removal for recovery from undervoltage, therefore remove any load from the PACK terminals or supply a
charge voltage to recover from UV after the cell voltages have returned to normal. The Quick Start
Sequence section is a good procedure to check the basic operation of the board. If the board has been
used for stacking evaluation be sure the R6 and R7 resistors have been replaced.
3.6 Changing Configuration or Conditions
If the board is modified to change the IC or other components or is operated at an expanded temperature
range, be sure to check component temperatures and other operating characteristics to be sure the board
does not provide a hazard in evaluation. A sample IC device may allow more current flow with higher
surface temperatures. Alternate FETs may require a change to the gate resistor to provide an appropriate
switching time.
4 bq77905EVM Circuit Module Schematic
This section contains information on other EVM features.
4.1 Alternate FETs
The EVM has TO-220 footprints for use as test points or power FETs as options for evaluation.
4.2 BATT Transient Pattern
D1 is a pattern for a TVS on the battery input terminals, if desired.
4.3 Other Uninstalled Components
The bq77905 EVM contains patterns for cell count configuration and stacking interface. Refer to the
schematic diagram and Section 3 for additional information.

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5 Circuit Module Physical Layouts
This section contains the printed-circuit board (PCB) layout, assembly drawings, and schematic for the
bq77905 circuit module.
5.1 Board Layout
This section shows the PCB layers and assembly drawing for the bq77905 module (see Figure 6 through
Figure 11). The board is a single sided assembly, no components are located on the bottom.
Figure 6. Top Silk Screen
Figure 7. Top Assembly
Figure 8. Top Layer

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Figure 9. Internal Layer 1
Figure 10. Internal Layer 2
Figure 11. Bottom Layer