DRV8306: Charge Pump Failure

Onkar Bhakare

Part Number: DRV8306

I'm using DRV8306 in my motor control application. I am facing issue during measurement of voltage across inline sense resistor. When I connect the reference terminal of probe to switch node, charge pump fails and driver enters into fault mode.This results into permanent failure of charge pump and no further switching observed at CPL and CPH pins after this incident. I am interested to know reason behind this.

over 6 years ago

0 Adam Sidelsky over 6 years ago

TI__Guru 65170 points

Onkar,

Please show a schematic of your circuit and where you are measuring including the scope probe GND.

Regards,

-Adam

0 Onkar Bhakare over 6 years ago in reply to Adam Sidelsky

Intellectual 550 points

0 Adam Sidelsky over 6 years ago in reply to Onkar Bhakare

TI__Guru 65170 points

Onkar,

Likely the issue is that you are shorting the motor switch node to GND when you add the probe reference terminal.

What you should do is use two single ended probes, one on either side of the sense resistor, then connect the two probe reference terminals to the PCB GND. Then use the math function on the scope to find the difference and therefore the drop across the resistor.

Regards,

-Adam

0 Onkar Bhakare over 6 years ago in reply to Adam Sidelsky

Intellectual 550 points

But I didn't understand why and how it affects the charge pump ?. There was no damage to MOSFETs but charge pump failed permanently.

0 Adam Sidelsky over 6 years ago in reply to Onkar Bhakare

TI__Guru 65170 points

Onkar,

Actually you are missing a connection in your schematic drawing, there is a connection from the switch node to the SHx pins on the DRV.

The SHx node does have a connection to the charge pump through the body diodes of the internal FETs so it is possible there was an undershoot event that damaged the charge pump due to a short to GND.

Please see figure 12 in the datasheet.

It is recommended not to use the GND reference of a scope at any node where there is voltage present.

Regards,

-Adam

0 Onkar Bhakare over 6 years ago in reply to Adam Sidelsky

Intellectual 550 points

Thanks Adam

0 Onkar Bhakare over 6 years ago in reply to Onkar Bhakare

Intellectual 550 points

But in this case internal body diodes will be in reverse bias so how charge pump can be shorted to ground ?

0 Adam Sidelsky over 6 years ago in reply to Onkar Bhakare

TI__Guru 65170 points

Onkar,

The VGS clamp will conduct the charge pump voltage out to the SHx node if the SHx node is shorted to GND and damage the internal charge pump components.

As designed, if the VGS clamp sees more than ~16V, it will break down and conduct to save the external FET from damage. Since the SHx node would be at 10V and the VCP at 20V usually, when the SHx node is shorted to GND, the VGS clamp sees 20V differentially and will conduct.

Regards,

-Adam

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DRV8306: Charge Pump Failure