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DRV8301 GVDD fall when PVDD increase beyond 28V.

theophile.alary
Prodigy 160 points
Other Parts Discussed in Thread: DRV8301

Hello,

I'm trying to make work my custom board featuring a DRV8301. As long as PVDD remains below 28V, the motor turns well, but as soon as I increased the voltage beyond, GVDD start becoming very noisy (a square wave at switching frequency, with low dutycycle, is visible on the GVDD and BST_x pins), and if I continue to increase PVDD voltage, a little more (let's say 28.3V), the DRV8301 triggers a fault (0x600 in SR1), and stop switching.

Capacitor (X7R or X5R) are about the same values and voltage rating than those of the DRV8301-HC2 kit, and below 28V, waveforms appear to be clean on all pin (a small ripple is present on PVDD though but I wonder less than 200mV pp should be acceptable ?), even if current measurement is noisy (1mOhm shunt at no load (10W, board is designed to run up to 55V, 40A continuous).

What is really strange is the threshold which does not change with switching frequency or when increasing GVDD cap.

An other important thing : when motor is disconnected, the problem does not occur (up to 30V, maximum voltage of the power supply I'm using)

Any idea ? 

Thank you for any suggestion !

  • 0
    Prodigy 160 points
    Actually, the same problem appears with no load, but when PVDD is a bit higher (from 30V), and waveform are more like triangle than squares...

    I'll disconnect mosfet gates and perform a new try...
  • 0 in reply to theophile.alary
    Prodigy 160 points

    When all mosfet gates are disconnected, the problem disappears. As soon as I connect only one gate, its happens again. Mosfet have a typ. Qg tot.of 170nC and switching frequency is 16 kHz, so I think the DRV8301 is able to provide enough current.

  • 0 in reply to theophile.alary
    TI__Guru** 114905 points
    Hi Theopile,

    Our expert has been contacted and should reply soon.
  • 0 in reply to Rick Duncan
    Prodigy 160 points
    Other information : I've used 4.7uf cap on AVDD and DVDD instead of the recommended value of 1 uf. I will test as soon as new DRV8301 IC will be delivered (I burned the all 3 circuits by making shortcuts will doing measurements)
  • 0 in reply to theophile.alary
    Prodigy 160 points
    I tried to put 4.7 uF caps for DVDD and AVDD on DRV8301 HC C2, to see if what happens, but signals seems to remain as they should be whatever the voltage applied on PVDD.
  • 0
    TI__Mastermind 21320 points

    Hi,

    It is not recommended to change the AVDD and DVDD capacitors from 1uF.

    Can you share the schematic/layout for this board? Have you confirmed this on multiple boards? Please also confirm the PowerPAD connection of the device, it is the ground for the charge pump.

    I would also check the CP1, CP2, GVDD pins for any type of short circuit or low-impedance path.

  • 0 in reply to Nicholas Oborny
    Prodigy 160 points

    Hello Nick,

    Shame on me, I checked the capacitor at CP pins, and instead of being a 22nF as written on the tape of capacitor I have used, it was a 470nF capacitor. The voltage rating of these capacitor is probably lower than the 100V I was expecting, as it is in 0603 package. (probably 10 or 16V, I use this value of capacitance mainly for the Vcore pin of MSP430 MCU), and probably the dielectric began to breakdown at 28V, but as the charge pump immediately stopped to work, it has protected the capacitor ?

    This is a board I design for my second employer, I will check at the end of this week if it changing the capacitor solves the problem, but I'm quite sure it will ! (I've checked the point you mention, and no short circuit have been detected. Concerning the power pad, I solder it first (with a hot air gun) ; I check that the DRV8301 is strongly fixed, then solder the other pins with a solder iron.

    Thank you for your support.

    Theo

  • 0 in reply to theophile.alary
    TI__Mastermind 21320 points

    Hi Theo,

    That is a tricky one, good find. Thanks for verifying the remaining points. Let me know how the testing goes.