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BQ25302: TS and REGN pin without USB

Ue
Genius 16285 points
Part Number: BQ25302

Hi all

My customer is working on a design with the BQ25302 and they have this question:

How do the TS and the REGN pins behave when USB is not connected ?

Are they tristate ? What is the internal circuit one has to consider ?

They want to monitor the battery temperature with the uC and at the same time the NTC is connected to the TS pin.

The reference voltage for the NTC is generated by the REGN pin of the BQ25302. If the battery is charged from the USB this works fine.

If the battery is discharged and there is no USB cable connected the REGN voltage is no longer there and they cannot read out the NTC.

Their idea is to put a high level at the ADC2_NTC_REF pin of the uC and to then read out the NTC_OF_Battery pin with the ADC of the uC.

They will do this only if no USB cable is connected. As soon as a USB cable is connected the ADC2_NTC_REF pin will be reconfigured and has again the ADC reference function.

Please also look at the schematic copied below and comment if this works as expected.

Best regards

Ueli

  • 0
    TI__Mastermind 24075 points

    Hi,

       REGN is part of the input source powerup sequence, so you would need a valid VBUS source for the REGN rail to come up. For the other design forcing high voltage on MCU pin, I would recommend testing with MCU and EVM setup to verify if it would work.

  • 0 in reply to Kedar Manishankar
    TI__Genius 16285 points

    Hi Kedar

    Thank you for the quick first reply.

    Let me reiterate the customer questions:

    How do the TS and the REGN pins behave when USB is not connected ?

    Are they tristate ? What is the internal circuit one has to consider ?

    Please also look at the schematic copied and comment if this works as expected.

    Please work on these and provide feedback.

    Best regards

    Ueli

  • +1 in reply to Ue
    TI__Mastermind 24075 points

    Hi,

       TS voltage is detected as a % of the pull up rail. In this case, REGN is used as the pullup rail for the internal comparator network detecting which TS mode of operation you are in.

    For customer application, it should be possible to source a voltage on REGN from an external source (when USB is disconnected) and continue to monitor the midpoint of TS resistor divider to monitor battery temperature. As both new pull up rail, and voltage at mid point of TS network are known by MCU, MCU can calculate battery temperature. It is better to connect the external voltage source on REGN through a diode. Recommended to still test on prototype or EVM.

  • +1
    TI__Genius 16285 points

    Hi Kedar

    Thank you for this additional input.

    Best regards

    Ueli