• State Resolved
  • Locked Locked
  • Replies 3 replies
  • Subscribers 62 subscribers
  • Views 516 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

Original question:

BQ25703A: bq25703A / ADC_ FULLSCALE

BQ25703A: bq25703A / ADC_ FULLSCALE, current shunt resistors, and LSB register values

Ishaan Govindarajan
Prodigy 20 points
Part Number: BQ25703A
Other Parts Discussed in Thread: BQ25703

Hi,

I'm using the BQ25703 for a low current solar application and have several questions regarding using a larger current shunt and changing gain values:

1) When changing ADC_FULLSCALE to 2.04V in the ADCOption() register, are all the LSB values for all the ADC registers affected (2/3rd their original datasheet value) or just the PSYS and CMPIN registers?

2) Does changing this ADC_FULLSCALE affect the resolution of any of the non-ADC registers, like the MinSystemVoltage() and IIN_HOST()?

3) Would doubling the IADPT Amplifier Ratio from 20x to 40x also double the resolution of the ADCIIN(), IIN_HOST() and IIN_DPM() registers?

4) Would using a 20mOhm charge shunt resistor (Rsr) double the resolution of the ChargeCurrent() and ADCIBAT() registers?

5) Related to the previous question, would using a 20mOhm input current shunt (Rac) double the resolution of ADCIIN(), IIN_HOST() and IIN_DPM() registers?

Sorry for the barrage of questions, but the datasheet wasn't super clear about the effects of changing these gain and shunt values. Thanks in advance,

-Ishaan

  • 0
    TI__Guru 56650 points
    Ishaan，
    1. If ADC_FULLSCALE is set to 2.04V, all the LSB values for all the ADC registers follows that change.
    2. ADC is a voltage measurement, it cannot change MinSystemVoltage() and IIN_HOST() resolution.
    3. IADPT Amplifier Ratio from 20x to 40x is independent from the ADC resolution.
    4. ADC is a voltage measurement, it cannot change Vsrp-srn result and resolution.
    5. ADC is a voltage measurement, it cannot change Vacp-acn result and resolution.
  • 0 in reply to Wang5577
    Prodigy 20 points

    Hi Wang,

    Thanks for the follow up. I should clarify my intentions:

    Since our system deals with relatively low battery charge current, discharge current, and adapter input current, I want to see if I can increase the current sensing resolution, acknowledging that it will decrease the sensing range. I think the following questions might make more sense:

    1) By using a 20mOhm input current shunt (Rac) and changing the IADPT_GAIN to 40x, will the IIN_HOST() and IIN_DPM() registers have a 12.5mA LSB resolution?

    2) By using a 20mOhm input current shunt (Rac) and changing the ADC_FULLSCALE to 2.04V, will the ADCIIN() register have a ~16.6mA LSB resolution?

    3) By using a 20mOhm battery current shunt (Rsr), will the IDCHG_VTH bits in PROCHOTOption0() have a 256mA LSB resolution?

    4) By using a 20mOhm battery current shunt (Rsr) and changing the ADC_FULLSCALE to 2.04V, will the ADC ICHG() and IDCHG() registers have a LSB resolution of ~21.3mA and ~85.3 mA respectively? 

    Thanks! -Ishaan

  • 0 in reply to Ishaan Govindarajan
    TI__Guru 56650 points

    Ishaan,

    1.  40x IADPT_GAIN cannot change the IIN_HOST() and IIN_DPM() gain. If original  IIN_HOST() and IIN_DPM() resolution is 50mA. 20mohm Rac can make 25mA resolution.

    2. With 10mohm Rac and 3.06V ADC scale range, the ADCIIN() resolution is 50mA. If use 20mohm Rac and 3.06V ADC scale range, the ADCIIN() resolution is 25mA. If use 20mohm Rac and 2.04V ADC scale range, the ADCIIN() resolution is 16.7mA.

    3. By using a 20mOhm battery current shunt (Rsr), the IDCHG_VTH bits in PROCHOTOption0() has a 256mA LSB resolution.

    4) By using a 20mOhm battery current shunt (Rsr) and changing the ADC_FULLSCALE to 2.04V, the ADC ICHG() and IDCHG() registers have a LSB resolution of ~21.3mA and ~85.3 mA respectively.