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DRV8323R: Voltage of VM, VDRAIN

KIM Andy
Expert 2530 points
Part Number: DRV8323R

HI

We separated VM and VDRAIN from the PCB as shown below.

They are controlled from different external power sources (Vs1, Vs2).

This is a condition for disconnecting the logic power and DCLINK power separately.

After turning on the power to the VM, the Enable signal is set to High and the power of the VDRAIN stage is cut off (Vs2 is cut off in the figure).

At this time, the voltage corresponding to VM is measured at VDRAIN.

Since the power of Vs2 is cut off, if all the capacitors connected to VDRAIN are discharged, the voltage of VDRAIN should be 0V.

However, even if the capacitor is discharged to 0 V instantaneously, it will continue to charge slowly and generate voltage.

It seems as if the power of the VM charges the capacitor of the VDRAIN stage by the internal circuit. Is it abnormal behavior?

  • 0
    TI__Guru 62390 points

    Kim,

    VM and VDRAIN should not be more than 5V different as internally the charge pump and protection circuitry are connected to both VM and VDRAIN. Since the high side gate and source are shorted when the high side is off, you may see charge pump voltage at the SHX/GHX node but since VGS is 0, the FET is off.

    Regards,

    -Adam