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DRV8701: DRV8701E don't start or stop for a while at load

Ilkay
Intellectual 310 points
Part Number: DRV8701

Hi All

I'm using DRV8701E version with 500W 24V DC motor. I used soft start start almost %10 and increase %10 in 1 sec to max. speed. I tried a lot of posibility for soft start. I also tried 700Hz to 20kHz PWM signals but I didn't solve that. 2200uF capacitor placed + and - lines.

If I used motor with no load or small load, there is no problem. If I will use with normal load, motor don't start or stop after for a while and give fault.

I checked AVDD and VCP are OK when fault occur. Two options are External FET overload and Pre-driver fault. 

I used IRF1405 which Qg is typical 170 nC (Max. 260 nC). I think mosfet Qg is a problem. I will check three different mosfet tomorrow which are IXTP110N055T2 (110A), IXTP140N055T2 (140A), IXTP200N055T2 (200A). Qg are small than 100 nC. 

Do you have any idea what is problem for this ? I attached schematic below.

  • 0
    TI__Guru 56650 points

    llkay,

    For a DC motor, the load is proportional to the winding current. The soft start needs to check the output current slew rate. It is related to the output voltage ramp-up. But, the output voltage ramp-up is not same as the output current ramp-up. That is why no load is no problem, the normal load don't start or stop after for a while because soft start current level is different.

    Please check output current to understand the soft start.

  • 0 in reply to Wang5577
    Intellectual 310 points

    Dear Wang Li

    Thank you for answer. I changed mosfets but it don't affect. After that, I checked my soft start algorithm than I solved issue which added current control to soft start algorithm.