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BQ24715: /BATDRV gate waveform

Sam Ting
Expert 3630 points
Part Number: BQ24715

Hi team,

Could you comment on whether the gate waveform of /BATDRV is normal? After adding 3A load to the system, the ripple will become larger, and the battery status is close to full charge.
Is it affected by the input voltage ripple? Because we found that the peak-to-peak value of the VIN ripple voltage is about 2V. Thanks for your support!

CH1: VIN (19V); CH2: VSYS; CH3: VBAT (3S); CH4: /BATDRV

Best regards,
Sam Ting

  • 0
    TI__Genius 11850 points

    Hi Sam,

     

    In order to turn the BATFET on, /BATDRV goes approximately 6V below SRN. Since VIN, VSYS, and VBAT in your waveform all have significant ripple, it is not surprising that /BATDRV has ripple as well.

     

    Overall, it seems like the ripple is caused by instability with the 3A system load connected, not a problem with /BATDRV itself. The ripple frequency is <10 kHz, which is much lower than the converter's switching frequency, so I don't think the ripple is directly caused by the converter either. What kind of load do you have connected to VSYS? Is it a 3A e-load in constant current mode?

     

    Best regards,

    Angelo

  • 0 in reply to Angelo Zhang87
    TI__Expert 3630 points

    Hi Angelo,

    Yes, it is 3A e-load in CC mode.

    Best regards,

    Sam Ting

  • 0 in reply to Sam Ting
    TI__Genius 11850 points

    Hi Sam,

     

    Can you please share the schematic and capture some waveforms at different load current levels (for example, 1A, 2A, and 3A) so we can see how the ripple is affected? Also, are you charging the battery at the same time while you are powering the 3A load? If so, what is the charge current?

     

    Best regards,

    Angelo

  • 0 in reply to Angelo Zhang87
    TI__Expert 3630 points

    Hi Angelo,

     

    After reducing the e-load from 3A to 2A, the ripple becomes smaller. The problem only occurs when it is almost full charged (with a capacity of 99% to 100% from gauge) and the fast charge current is set to 1.65A.  

     

    Best regards,

    Sam Ting

  • +1 in reply to Sam Ting
    TI__Genius 11850 points

    Hi Sam,

     

    Thanks for sharing the schematic offline. We can continue the discussion via email.

     

    Best regards,

    Angelo