BQ25756EVM: Input Rsense current reading not as expected

Part Number: BQ25756EVM
Other Parts Discussed in Thread: BQ25756, BQSTUDIO

Tool/software:

Hi,

We are evaluating BQ25756 Charger IC, In which we observed Rsense current reading from Battery management studio (BQstudio) is showing incorrect value.
Observation: 
IAC_ADC- use field view  = 2334mA (Read value)
ICHG_REG = 800mA (Set value)
IBAT_ADC-use field view = 668mA (Read Value)
And the real value on ammeter is 0.996A at 24V input and battery voltage is 27622mV.

Our observation is IAC_ADC is showing very high value when compared with ammeter.

Thanks,
Mukunda M

  • Hi Mukunda,

    Can you measure the charge current with an ammeter on the charge current? It seems as though the device is charging at the proper current based on the input voltage and current and the output voltage.

    The ADC on the BQ25756 is meant as a general indicator of device functionality and can provide information about how the device is operating, but if accurate measurements are needed, we recommend using an external measurement device such as a battery monitor where the ADC is the main purpose of the device.

    Best regards,
    Michael Bradbourne

  • Hi Micheal,

    Charge current is almost similar to IBAT_ADC in BQ studio. We verified it with ammeter as well, It is showing similar value as IBAT_ADC.

    For the ADC we do not want highly accurate input current measurement, But as of now we are seeing double the value (IAC_ADC- use field view  = 2334mA, real value being 0.996A). So we want to know if some setting needs to be modified, Could be a scaling issue which can be resolved through a minor change.

    Thanks,
    Mukunda M

  • HI Mukunda,

    I believe most of the ADC error comes from an offset or is induced by switching noise. What does the IAC_ADC look like across different currents?

    Best regards,
    Michael