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DRV8301 supply current versus transistor total charge

Lukas Palkovic39
Intellectual 420 points
Other Parts Discussed in Thread: DRV8301, CSD18533Q5A

Hello everyone,

I am working on a desing with DRV8301.

It works fine but I experience the circuit is warmer than expected.

The plan is to drive 3 or more Mosfets in parallel.

I have more prototypes and I measured the current to PVDD.

When I use 6pcs (1 in parallel) CSD18533Q5A with 29nC @ 10V with 45kHz and 8.3V I expect Igate = 29e-9 * 6 * 45e3 = 8mA

The supply current is 22mA. I'd expect slightly more than 8mA, but 22mA is too much (though still bellow 30mA maximum for DRV8301)
 

When I use 18pcs IRQF (59nC @10V), the current is much larger - 90mA, though theoretical one is Igate = 59e-9*18*45e3 = 50mA

I measured worse (150mA @45kHz) values for 6pcs of NTMFS4935NT1G (50nC @10V) but was not able to reproduce it other day with other day (then it was 30mA - still out of expected 14mA ). This actually initiated the investigation.

1. Can a "rough" soldering (hot air 400 degC) affect the transistor total charge in some way?

2. Can a variation of transistor parameters contribute to these results so significantly?

3. How much of the supply current goes to "Igate" and how much is consumed "internally".

4. Is 30mA a value that must not be exceeded or is it somehow limited internally?

5. I there anything else that should be taken into account and I might be omitting it?

Note: Constant 56mA supplying buck converter have been substracted from the real measurements.

Thank you in advance

  • 0
    TI__Guru** 114905 points
    Hi Lukas,

    Are you measuring PVDD or GVDD current when switching? The calculation is for GVDD, the gate drive supply.

    How are you measuring this current; current probe, current meter, or some other method? What is the accuracy of the measurement device?
  • 0
    TI__Mastermind 21305 points

    Lukas,

    Some additional comments.

    1. I am unsure here. You would have to check on the Power MOSFET forums.

    2. Variation could have a small effect, but not significant. Qg MAX at 10 V = 36 nC

    3. The DRV8301 consumes 5-10 mA nominally. So this explains some of the missing "supply current".

    4. 30 mA is the MAX recommend draw from the GVDD regulator. It is not clamped internally but this should not be exceeded.

    5. As Rick mentioned, how are you measuring the current? Can you share the schematic?

  • 0 in reply to Nicholas Oborny
    Intellectual 420 points

    Hi Nicholas and Rick,

    Thank you both for your answers.

    I measure voltage dropout on 1R resistor in the PVDD and PVDD2,3 and subtract the value measured when the transistors are not switching.

    The current is proportional to the frequency (not mentioned in the original post).

  • 0 in reply to Lukas Palkovic39
    TI__Mastermind 21305 points

    Since PVDD2 supplies the buck regulator, is there any 3.3V devices that consume more power when the motor is switching? This might explain some of the current.

    Yes, it is expected the current will increase with switching frequency. The MOSFETs will require more charge.

  • 0 in reply to Nicholas Oborny
    Intellectual 420 points
    Hi,
    no, there is a negligible change in the current of the 3.3V circuit (different calculation).


    The fact that the gates are driven from GVDD helped me to identify that there is a DC/DC converter stabilizing some 10.5V on GVDD and it requires higher current (the power supply is 8.4V).
    Then taking into account efficiency of the stabilizer, burning energy on gate resistors and internal gate resistance, internal current of DRV it seems my measurements fit the theory.

    I even measured the gate charge "estimating of integral of the charging current seen on oscilloscope" and it's in range +10% from catalog value.

    The mentioned "150mA @45kHz) values for 6pcs of NTMFS4935NT1G (50nC @10V)" problem remains without explication and was not reproduced.

    Thank you for your help.