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BQ76200: not working

Dinesh Gread2
Intellectual 340 points
Part Number: BQ76200

Hi Ti,

i am using Bq76200 and Enable charge and discharge MOSFET together , i am just trying to make a switch , Here the problem is the gate voltage is not started or boost , but at boot cap the voltage is perfectly ok.

can you please help me what to do to make circuit work.

the input is 40V i am giving  at boot cap 48v i can measure. At charge Mosfet gate i am not able to receive  48V after enable signal at input of controller Bq76200.

Pre-charge is working fine .

MOSFET :IAUT300N10S5N015ATMA1

  • 0
    TI__Guru 54715 points

    Hi Dinesh,

    The problem is likely the value of C66.  0.1 uF will likely cause the charge pump to dump into this capacitor during DSG turn on pulling the charge pump into UVLO, turning off the drivers and leading to a cycling.  See the application note https://www.ti.com/lit/pdf/slua794 for example waveforms and more description of the part.  C66 should be 10 nF typically.  The part will work better if C66 is smaller.  C61 may be ok but is also typically recommended to be 10 nF.  If the 40IN is very dynamic during operation a smaller C61 is helpful to avoid UVLO from the variation of the 40IN vs the filtered BAT reference.

    At 40V DSG will have a large step at turn on, it would be best to optimize turn on with a resistor at R12, see the application note.  The Zener and 100 ohm between DSG and PACK pins may be helpful also to avoid internal losses at turn on.  R10 and R11 should likely have some non-zero value also, 100 ohm to a few k ohm will isolate the pins from any transients on the 40IN bus.

  • 0 in reply to WM5295
    Intellectual 340 points

    Hello ,

    Thanks for clarification.

    the circuit works for 1 time but i have tried to connect a electronic load to the end of mosfet and than this problem started.

    Should i change the the controller with new one?

    Because i am giving enable to the controller and the DSG and CHG pin not increasing the voltage to 50V for gate of MOSFET also i have used 1uf for BOOT cap as i have 2 Power MOS.

    in depth i have two electronic switch where i have two driver and two bunch of MOSFET can you please check below circuit if i am doing something wrong.

    I will change R10, R11,R12 ,R13,R14,15 with 100E, C61 and C66,C67,C62 with 10nf,

    may be i dont have 10nf can i change it with 22 nf ??

    Can you please comment , as per your suggestion it looks like the out is loaded by 2 capacitor and with 2 resistor. Should i replace with one RC or the below circuit is fine from driver side. R66,C66,R67, C67.

  • 0 in reply to Dinesh Gread2
    Intellectual 340 points

    Hello Ti Team,

    Could you please give your suggestions based on my query in above i got stuck and wait for your reply.

    Thanks,

    Dinesh Gread

  • 0 in reply to Dinesh Gread2
    TI__Guru 54715 points

    Hi Dinesh,

    I think each part should have its own filter.  If 10 nF is not available I would use smaller capacitors rather than 22nF.

    An electronic load may have large output capacitors, it could look a lot like a short circuit even when "off" due to the large capacitance.

  • 0 in reply to WM5295
    Intellectual 340 points

    Hello Sir,

    i found 6.8nf and connect C66 nd C67.

    At gate of each mos i have replace it with 100E from 0E.(R10,11,12,13,14 15)

    i have change the controller again i lost 3 nos, Now it started to work with new .

    1. But request you to please explane me why this controller gone bad if i connect  electronic load to the out of the MOSFET.

    2. Once the MOSFET started work can i give step load at once as like 30 Amp ,or 40 Amp.

    3. Is there any thing else i need to connect to driver to save it.

    Also please share your recommendation if any this is missed.

  • 0 in reply to Dinesh Gread2
    TI__Guru 54715 points

    Hi Dinesh,

    1. An electronic load should have no output when connected, I would not expect it to damage the driver.  When you connect the batteries the FETs should be off, the ESD capacitors will divide some voltage to the OUT.  Again it should not cause any damage.  If the load is connected with a voltage present to OUT, again the ESD capacitors will divide voltage to the battery pack inputs.  This will drop off with time.  Again I don't see a reason for damage.

    2. Seems like normal expected operation, good.

    3. I don't recognize a reason for issue.  You might check to see that the 12V stays at 12V or if there is some transient.  Also if you know what is damaged on the driver you may know where to look.  If a pin draws excessive current or limits its voltage it could indicate it encountered a damaging signal.