DRV8412: Vreg is not up

Wee Chang Liew

Part Number: DRV8412

Hi,

I have issue where the Vreg is not always up, sometime is does, sometime it doesn't. When Vreg doesn't go up to 3.3V, all logic circuit are not responding.

When it is up, it looks like:

When it doesn't, it looks like:

Anyone has any similar experience? any clues to troubleshoot?

over 6 years ago

0 Rick Duncan over 6 years ago

TI__Guru** 114905 points

Hi Wee Chang,

Have you confirmed this behavior on multiple parts and multiple boards?

Can you provide a scope capture of the VDD vs VREG ramp zoomed in as much a possible?

Is this related to the post: e2e.ti.com/.../1636338 vreg#1636338 ?

0 Wee Chang Liew over 6 years ago in reply to Rick Duncan

Prodigy 100 points

Hi Duncan,

Yes, it happens on multiple parts and multiple boards.

Yes, it is linked to the previous post. I thought the issue has resolved, but it doesn't, someone filtered the boards to reach me so I thought the issue has been resolved.

The behaviour is random. Out of 10 power cycles, it may have upto 80% chance the Vreg doesn't up.

I have 2 same parts on the ame PCB, one drive a stepper motor, and the other drives 2 DC motor.

Both suffer the same issue but probability of occurance is much more on the stepper driver than the DC driver.

I'll get the signal captured as per ur request.

0 Wee Chang Liew over 6 years ago in reply to Wee Chang Liew

Prodigy 100 points

Hi Rick,

If the thermal pad is not connected to GND, due to PCBA process, will it change the ground reference? in the datasheet, it only mentioned 'should be connected to GND'. Does thermal pad has electrical connection?

0 Rick Duncan over 6 years ago in reply to Wee Chang Liew

TI__Guru** 114905 points

Hi Wee Chang,

The thermal pad is not used for electrical connection, but there are indirect connections (substrate diodes) which is why the recommendation to connect to GND.

0 Wee Chang Liew over 6 years ago in reply to Rick Duncan

Prodigy 100 points

Hi Rick,

Thanks for looking after the thread, I think I have found the root cause of the issue.

Vreg has been driven by the logic input pin, which power rail start much earlier than Vdd.

I removed this condition, the Vreg starts up normally.

By removing the potential divider on SHDN pin, which is the root cause of the delay of VDD to other logic power. the problem resolved.

Thank you very much for your support.

0 Wee Chang Liew over 6 years ago in reply to Wee Chang Liew

Prodigy 100 points

Added improved condition snapshot:

0 Rick Duncan over 6 years ago in reply to Wee Chang Liew

TI__Guru** 114905 points

Hi Wee Chang,

Thank you for the information.

We are glad to hear the problem is resolved, but we will continue to investigate. If we find anything, we will let you know.

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DRV8412: Vreg is not up