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 its VAC/VBUS pin (using the VINDPM feature), BAT pin
(as part of normal termination), and TS pin (through its 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, make sure shunt jp16 is in place.
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 connectors in order 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 ensure that the sensing leads are
connected in order to prevent accidental overvoltage by the power leads
For precise measurements of input and output currents,
especially battery charging current regulation near termination, the current
meter in series with the battery or battery simulator should not be set to
auto-range and may need 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 BMS026 EVM.