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BQ79631-Q1: CSADC current value always near zero

Daniele Guazzarotto
Prodigy 20 points
Part Number: BQ79631-Q1
Other Parts Discussed in Thread: BQ79616

Hi, 

I'm facing a problem with the shunt current reading (CURRENT HI/MID/LO registers).

The BQ79631's Main and CS ADCs are configured in Continuous run (MAIN_MODE = 0x10).

In this case, I'm giving a single start of conversion command together within the ADC configuration. The problem is that the current value read back from the CURRENT HI/MID/LO registers is always near 0 (raw value from ADC) and the conversion to ampers is also accordingly in the order of tens of mA. I tried to apply different values of differential voltages between SRP and SRN pins (5-10-20-30 mV), but with the same result. 

I also noted that the auxiliary current value, sampled through the main ADC (CSAUX_HI/LO registers), is correctly sampled and agrees with the voltage applied to the SRP-SRN pins.

I think that this problem could be related to the ADC configuration that I used.

Could you please explain how the CS ADC works and how to properly configure it to obtain a correct reading?

Thanks in advance,

Daniele

  • 0
    TI__Intellectual 2365 points

    Hi Daniele,

    Could you let me know what configuration steps you did before running CS ADC sample? Also, do you observe this on one device or multiple devices?

    thank you,

    Helen

  • 0 in reply to Helen Sun
    Prodigy 20 points

    Hi Helen, 

    Yes, I observed this behavior on two different devices.

    I'm currently using this configuration:

    BQ79600 -> BQ79631 -> BQ79616

    After the wakeup and auto address routine for the chain, the devices are configured as follows:

    - set number of connected Vsense

    - set GPIO's functions

    - Enable TSREF

    - Configure ADC_CONF1: 0xF7 

    - Configure COMM_TIMEOUT_CONF

    After this configuration, I execute the start of the conversion routine as follows:

    - configure ADC_CTRL1: 0x5E

    - configure ADC_CTRL3: 0x06

    After those configuration steps, I poll for the data every 10 ms. I receive correctly all the data sampled from the Main ADC (AUX CS current included), the only data that is not coherent is the one coming from the CURRENT HI/MID/LO registers.

    Little update, I tried also the Single Run mode, but with the same results.

  • 0 in reply to Daniele Guazzarotto
    TI__Intellectual 2365 points

    Hi Danielle,

    So you are able to read the correct values in CSAUX_HI/LO ok ? 

    Could you try the below:

    1.Below are the full configuration steps, could you try doing the full set up before starting CS_MAIN_GO?

    2. Could you try higher VCS_RANGE( for example 70mV) to see if you can read anything off the 3 registers?

    3. Try doing a single conversion, then wait >13ms before reading the 3 registers

    thanks,

    Helen

  • 0 in reply to Helen Sun
    Prodigy 20 points

    Hi Helen, 

    I tried to change the configuration.

    1. The Main and CS ADC is configured with single mode, no LPF and CS_DR 3 ms.

    3. I tried using the single-mode configuration with 100ms polling. The result is really strange. If I apply a voltage lower than 1.6mV to the shunt pin, I obtain a correct measurement. After this threshold, the current value starts to go down to 0 near 2mV. After that the reading is always near zero.

    2. Same as above. After 1.6mV the current goes down to zero.

  • 0 in reply to Daniele Guazzarotto
    TI__Intellectual 2365 points

    HI Daniele, 

    Could you please check the below:

    1. Please send a scope shot of srp/srn during the continuous mode measurement.

    2. Are you using the TI bq79631 GUI to read the registers? if not , can you download the TI GUI and check if the 3 registers read with the same test condition?

    3. Are you using a TI EVM for bq79631 or using a custom board? If using a custom board, can you send over a schematics for review?

    thank you,

    Helen