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BQ25713: Charger Noise

Saeedeh Ghaffari
Prodigy 100 points
Part Number: BQ25713

Our system has the following features:

  • Two batteries: primary and secondary
  • Primary can be swapped, but secondary is fixed
  • Support on-board charging for both batteries
  • Support the hot swap feature for the primary battery (i.e. a primary battery change without a reboot)
  • Support external DC power supply

To implement above features, two charger ICs (BQ25713B and BQ25713) are used on a single board daisy chained as shown below:

However, a significant noise is coupled to the system as soon as the external DC input is connected. And it increases as the batteries are becoming full. I've tried disabling the charging which made it worse, and changing the charging current had no effect.

Could someone advise what could be the cause of the noise? Perhaps the implementation is not correct, and to support all the features required on our system, we had to have another approach? 

 

  • 0
    TI__Mastermind 25800 points

    Hey Saeedeh,

    Just to make sure the nomenclature is correct, when you say primary and secondary, you DO NOT mean Non-rechargeable and Rechargeable? Primary and secondary are priorities correct, i.e. like 'main' battery and 'backup' battery?

    Second, do you have any schematic or waveforms to share of your system? Does a single charge show normal operation without the other present?

    Regards,

    Joel H

  • 0 in reply to Joel Hernandez II
    Prodigy 100 points

    Hi Joel,

    They are both rechargeable and act like main battery and backup battery as you said.

    • The system was tested without the main battery, and the noise was there when DC power supply is present.
    • To ensure that the external power supply itself is not a source of noise, I've also tested the system by bypassing the Charger ICs (removing the jumper resistors, so that the charger ICs were completely isolated and not a part of the circuitry). And supplied the SYS_VIN directly from the power supply, and the noise was gone.

    Here are the Schematics:

  • 0 in reply to Saeedeh Ghaffari
    TI__Mastermind 25800 points

    Hey Saeedeh, 

    Thanks for the schematic. I should have been a bit more clear with my question: 

    Have you tried each charger individually powered from the external supply? I am trying to determine if the noise is function of each charger on its own, or the daisy chain itself. 

    Can you take a waveform of the SYS output of the first charger by itself (you may remove R259 to isolate the second charger)

    And then please take a waveform of the SYS output of the second charger by itself (you may bias the Daisy chain rail directly)

    For each, please capture SYS pin voltage, SW1 pin voltage, SW2 pin voltage, and VBUS pin votlage or the output current

    Regards,

    Joel H