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BQ25886: Recommendation to measure TS pin

Eduardo Garcia68
Intellectual 385 points
Part Number: BQ25886
Other Parts Discussed in Thread: BQ25882

Hello:

We are using the BQ25886 and using the TS pin as recommended in the datasheet to limit charge from 0*C to 60*C. We have 

RT1 = 5.24kΩ

RT2 = 30.31kΩ

10k NTC

However we would also like to connect the TS pin to a microcontroller's ADC to measure the cell's temperature. However the voltage at said pin can swing over 3.3V at lower temperatures and damage our ADC.

 I wanted to ask if there is a way you would recommend for us to be able to measure this pin on an MCU's ADC that can go up to 3.3V. We were thinking to use an opamp to scale the voltage into the MCU. Maybe I am missing an easier way.

On a similar note, assume if I have a simple opamp that consumes very low power. Could I power it from the REGN pin to perform this function? Would it not be advisable? This is for a very cost sensitive application so removing BOM components is desired.

Thank you for your time,

Eduardo Garcia

  • 0
    TI__Guru*** 143980 points

    Hi Eduardo,

    You opamp idea is the way the go.  You will need an op-amp with high Z input in order to prevent loading the TS pin.  

    You can use REGN to power additional circuitry as long as the tested current of 20mA dc / 50mA fast tranisent for regulation.

    As an alternative, we have an I2C controlled version of BQ25886, BQ25882, with integrated ADC that reads the voltage at TS pin.  From that voltage, you can compute the thermistor value and therefore battery temperature.

    Regards,

    Jeff 

  • 0 in reply to Jeff F
    Intellectual 385 points

    Hi Jeff, thanks! I have seen the I2C alternatives but for this very cost sensitive application the savings on using the other one merit the use of the opamp. I will re-evaluate however. Thank you!

    -Eduardo