BQ40Z50EVM-561: The difference between reported pack pin voltage and measured pack pin voltage

John Chou62

Intellectual 2070 points

Part Number: BQ40Z50EVM-561
Other Parts Discussed in Thread: BQ40Z50

hi Team,

it's observed from the bq40z50 EVM.

it's calibrated with CFET and DFET ON, the SBS display and the multi meter measurements are the same value for pack pin voltage

however, once we turn off the CFET by CFET toggle command

the SBS report voltage is ~40mV less than the measured voltage.

1. what might be causing the difference from the reported voltage and measured voltage? measured voltage to be ~40mV higher

2. if a loader is connected to the P+ (with no load) the reported voltage will become the same with measured voltage again (within 1~2mV)

3. measuring on either side of the R12 on the EVM board, voltage on the side of R12 to Pack Pin is lower than R12 to connector side around 40mV, but why this difference doesn't show when CFET is ON

is there an explanation for the observation?

Thanks for the help

over 6 years ago

0 Batt over 6 years ago

TI__Mastermind 42535 points

Hi John,

When you calibrate the gauge if the FETs are on, you will see BAT voltage at PACK. I usually calibrate with fets off and independent sourcemeters powering BAT and PACK and input the voltages measured at each end to the calibration screen. I believe what you are seeing is expected.

0 John Chou62 over 6 years ago in reply to Batt

TI__Intellectual 2070 points

hi Batt,

Thanks for your feedback.

i tried to calibrate it with both CHG and DSG FETs off. and using an independent power source at the pack pin. (at ~12V)

once calibrated.

with both FET ON.

PACK pin measured at the connector = 11970mV, SBS report pack voltage = 11970mV

with CHG FET OFF and DSG ON

PACK pin measured at the connector = 11600mV SBS report pack voltage = 11570mV -> 30 mV difference~!

we are wondering on why with CHG FET OFF it can introduce this difference~!? this can be seem on the EVM board

Thanks for the help

0 Batt over 6 years ago in reply to John Chou62

TI__Mastermind 42535 points

I'll check on this and reply back in a day.

0 Batt over 6 years ago in reply to Batt

TI__Mastermind 42535 points

Please give me until Friday to check this out for you.

0 John Chou62 over 6 years ago in reply to Batt

TI__Intellectual 2070 points

noted, Thanks for the help

0 Batt over 6 years ago in reply to John Chou62

TI__Mastermind 42535 points

Hi John,

The reason is because the afe draws power for the chg pump through the pack pin. Basically the fet driver comes through the pack pin.

Power management

Power management forum

BQ40Z50EVM-561: The difference between reported pack pin voltage and measured pack pin voltage