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BQ25713: Boost mode

lucien lu
Prodigy 20 points
Part Number: BQ25713

Hi,

We use BQ25713RSNR to charge a 2-cell battery.

Situation and Phenomenon:
Boost mode,VBUS 5V,VBAT 7.4V
We measure the boost-mode MOSFET Gate drive signal.
CH3: Highside Vgs(Q209)
CH1: Lowside Vgs
Vgs(th)=1V (Min.)
Low side MOSFET rise over Vgs(th) before highside fall bellow Vgs(th);
High side fall slowly, and there is a step when falling down.There is risk that the Vin may be shorted to Ground.

Question:

Please help refer to the attached schematic and test result and check if they are OK.

BQ25713_MOSFET Switching Dead time.docx

Thanks

  • 0
    TI__Expert 5330 points

    Hi Lucien,

    I took the following two captures on EVM.  I did this with VIN=5V and VBATT=7.4V and measured

    CH1 = Yellow = TP11 (LODRV)

    CH2 = BLUE = TP14 (HIDRV)

    CH3 = Purple = TP3 (SW)

    MATH = Red = CH2 - CH3

    Here I am seeing the expected dead time between GS of HIFET (red Math channel) and GS of LOFET (CH1).  Can you take captures with similar time scale so that we can compare?  Please be certain that all three channels are set to full bandwidth capture (on my scope/probes this is 500 MHz bandwidth), that you have the highest resolution (10 M data points on my scope) and that you are capturing on as narrow a timescale as possible, I'm doing 20 nS per division on the capture here.  These signals are very easy to alias, so following these steps is really important or you can get very confusing scope captures. 

    Here is what I captured for your reference, and if you can take similar captures we can compare.  I did not see any concern in your schematics that you sent.

    Here is the high-side FET turning on.

    And here is the High-side FET turning off

    Regards,

    Steve

  • 0 in reply to Steve Preissig
    TI__Expert 5330 points
    Hello Lucien,

    I haven't seen a response on this in a few weeks. Hopefully the provided scope captures and procedure were sufficient to help you resolve the issue, so I am going to close the ticket. If this is not the case, you can reopen the ticket and let me know the latest status.

    Regards,
    Steve