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.

BQ25890: REGN has ripple at Hi level

Part Number: BQ25890

Hi team,

Here's an issue from the customer may need your help:

The product is a Bluetooth speaker with output wattage Mono 10W Does the REGN voltage level of the BQ25890 have a ripple effect on the accuracy of battery temperature detection?

Basic conditions are as follows:

  1. VBUS is not plugged in
  2. The ADC Conversion rate is set at Start 1s Continuous Conversion
  3. The Bluetooth speaker is set at maximum volume

RENG waveform without playing music:

RENG waveform with playing music:

From the above two waveforms, it is found that when playing music, the REGN has riple at Hi level, and no Hi level is playing music without ripple.

The customer want to make sue if it will affect the accuracy of the battery temperature? What can be done to affect the accuracy of the battery temperature?

The Power map of the bluetooth speaker is as follows:

Could you help check this case? Thanks.

Best Regards,

Cherry

  • Cherry,

    In battery only mode without valid VBUS, the REGN LDO is usually off (except in boost mode).

    1. Referring to 8.2.8 Battery Monitor on the d/s, when battery monitor is active, the REGN power is enabled temporarily in short period for ADC measurements.
    2. For 1 second continuous conversion (CONV_RATE = 1), The battery monitor provides conversion result every 1 second automatically, then REGN is turned on every 1 second automatically.

    Thanks,

    Ning.

  • Hi Ning,

    Thanks for your help.

    The RENG's ripple is a little bit larger, as shown in the red box below.

    This will affect the voltage fluctuations of the TS, which will cause the BQ25890 internal ADC to detect a large error in the battery temperature. The customer would like to figure out the mechanism of the BQ25890 internal ADC. Could you help clarify this?

    The following figure is the actual measured waveform on the board, which is indeed larger:

    Thanks and regards,

    Cherry

  • Cherry,

    Referring to JEITA THERMISTOR COMPARATOR (BUCK MODE) and COLD/HOT THERMISTOR COMPARATOR (BOOST MODE) specs on the Electrical Characteristics table, it is the (VTS/VREGN)% (e.g. 44.74%) determining the temperature status, but not VREGN. The internal network is biased by REGN. The variation of REGN will be cancelled when the external network is biased by REGN. That's why Figure 14. TS Resistor Network uses REGN as pull-up, but not a random power supply.

    Thanks,

    Ning.