Helpful Tips - Texas Instruments BQ25638 Series User Manual

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3.2.5 Helpful Tips

1. The leads and cables to the various power supplies, batteries and loads have resistance. The current meters
also have series resistance. The charger dynamically reduces charge current depending on the voltage
sensed at the VBUS pin (using the VINDPM feature), BAT pin (as part of normal termination), and TS pin
(through the battery temperature monitoring feature via battery thermistor). Therefore, voltmeters must be
used to measure the voltage as close to the IC pins as possible instead of relying on the digital readouts of
the power supply. If a battery thermistor is not available, then that shunts JP11 and JP13 in place.
2. When using a source meter that can source and sink current as your battery simulator, TI highly
recommends adding a large (>=1000+ μF) capacitor at the EVM BATTERY and GND connector to prevent
oscillations at the BAT pin due to mismatched impedances of the charger output and source meter
input within their respective regulation loop bandwidths. Configuring the source meter for 4-wire sensing
eliminates the need for a separate voltmeter to measure the voltage at the BAT pin. When using 4-wire
sensing, always make sure that the sensing leads are properly connected to prevent accidental overvoltage
by the power leads.
3. For precise measurements of input and output current, especially near termination, the current meter in
series with the battery or battery simulator must not be set to auto-range and needs to be removed entirely.
An alternate method for measuring charge current is to either use an oscilloscope with hall effect current
probe or by a differential voltage measurement across the relevant sensing resistors populated on the
BQ25638xEVM.
SLUUCR0A – SEPTEMBER 2023 – REVISED DECEMBER 2023
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BQ25638x Evaluation Module 11