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  • TI Thinks Resolved

DRV8323: High current consumption while operating without load

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Replies: 8

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Part Number: DRV8323

Hi, I'm driving totally 18 MOSFET's with DRV8323RSRG used with MCU TMS320F28069. Total gate charge of single mosfet is 91nC. When I apply 45KHz pwm with 50% duty cycle (VDD 12V), supply current is approximately 170mA. Output voltages are always OK. But when the power supply voltage increases, the current consumption increases too and DRV starts heating. 

Measured values in various power supply voltage with no load: 

when DRV disabled:  12V:  50mA,

20V:  30mA

30V:  20mA

DRV enabled(without pwms): 12V: 70mA

     20V: 40mA

     30V: 30mA

all 3 phases active(18x active MOSFET) :  12V:170mA

20V: 210mA

30V: 230mA

only one phase active(any)(6x active MOSFET) : 12V: 100mA

     20V: 90mA

     30V: 90mA

I tried to adjust IDRIVE, TDRIVE, and also check deadbands on the scope if pwms don't cross, but that has no effect on curent consumption. 

Screenshots of VGS when supply was 12V:

high side VGS:

low side VGS: 

Please help if anybody knows what may cause this problem.

Thanks a lot. 

Tomas Vrsansky

  • Hello,

    Please share your schematic.

    Regards,

    -Adam

  • In reply to Adam Sidelsky:

    Hi,

    I enclose the schematics related to DRV. Device is composed of two boards, control and power part which are connected by 1.25mm pitch connectors. 

    Tomas Vrsansky

  • In reply to user5958720:

    Hi again,

    Maybe my original question was too complex, so I want to ask something straightforward.

    Is there any reason that the DRV driving current and power dissipation increases significantly with the VDD voltage? I expect lower current if an appropriate charge pump is used or constant current if linear regulator is used in the worst case. What approximately should be the right values? 

     

    After some additional experiments with IDRIVE and TDRIVE I achieved a small improvement on power consumption. Actual measurements are:

    VDD=10V -> 170mA total -> from which DRV charging current part=100mA (1W power)

    VDD=20V -> 190mA total-> from which DRV charging current part=150mA (3W power)

    VDD=30V -> 190mA total-> from which DRV charging current part=160mA (4.8W power)

    (PWM 45kHz 50%, with no load)

     

    I would be grateful for your response as soon as possible.

    Tomas Vrsansky

  • In reply to user5958720:

    Hello,

    Are you including current into VIN when mentioning the DRV charging current?

    According to all our information, the current should not increase as the VDD increases once the CP has exited doubler mode.

    Since you have three parallel FETs, have you tried with gate resistors or when installing only one of the three FETs for each HS or LS?

    Regards,

    -Adam

  • In reply to Adam Sidelsky:

    Hello, thank you so much for your quick reply,

    As the "DRV charging curent" I ment total current measured on power supply minus state, when DRV is enabled with PWMs off. 

    When I tried to solder only one FET for each side the current was as follow:

    10V supply -> 110mA total current

    20V supply -> 100mA total

    30V supply -> 90mA total

    -         When I subtract current when PWMs are off, the current consumed by “DRV charging” seems to be constant here.

    With 2 FET’s on each side:

    10V supply -> 140mA total

    20V supply -> 140mA total

    30V supply -> 140mA total

     

    As you suggested, I tried to add gate resistors (to each FET) with both 4R7 and 8R2 values, but any of these has effect on current consumption. I also watched the gate voltages on the scope, but I didn’t notice any undesirable ringing with or without the gate resistors.

    Thanks for your help.

    Tomas Vrsansky

  • In reply to user5958720:

    Tomas,

    I believe you are seeing the current of the Buck inside the chip. Can you confirm this is not the case?

    Regards,

    -Adam

  • In reply to Adam Sidelsky:

    Hi Adam, thanks for your reply,

    I do not think that the internal buck is the reason. When DRV is off and I supply MCU with 3.3V from that internal buck, the current consumption is OK which you can see too in my first post.    

    Regards,

    Tomas Vrsansky

  • In reply to user5958720:

    Tomas,

    Was this issue resolved?

    Regards,

    -Adam

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