DRV8412 will not start motor when hot.

Hi Steve,

I am assuming you are using your EVM. Is that correct?

Can you clarify your post? You stated that you have an overtemp fault in the description, but it looks like you are describing an overcurrent or undervoltage event (!FAULT = 0 & !OTW=1 when it is failing). Am I understanding this properly?

When you stop and re-start in <1 s, does the motor actually stop?

It may be that you are having overtemp issues. How much current is the motor consuming?

Are you sure the thermal pad is soldered down properly and there is a good thermal plane to dissipate the heat?

We are using our own board not an EVM.  Sorry on the over temperature fault confusion, I do not think we are getting an over temperature fault.  Yes, when we stop and re-start the motor for < 1 Sec, the motor does actually stop turning.  Our motor is consuming ~2A.  Yes, the thermal pad is soldered & the plane is ~1 IN^2.

The confusing part is that if we do not stop the motor, we can increase the ambient temperature up to 110 degC and to driver / motor combination work fine.

Hi Steve,

Thanks for clearing up the over temp fault.

Based on the fault pins, you are getting either an overcurrent or undervoltage. It is confusing that either one of these would appear because of temperature.

Do you have a second board or motor to swap out to isolate the problem?

If you have a current probe, can you look at the current out of the DRV8412? 

Can you check for a bulk cap near the DRV8412 plus 1uF caps next to the GVDD_x pins?

Do you have inductors or ferrite beads at the outputs prior to connecting the two outputs in parallel?

If you can send the schematic and scope shots of the current, that should help narrow down the problem.

5483.DRV8412.pdf

This is occurring on multiple boards and motors so it is not an isolated incident.

The is a 100uF bulk capacitor plus a 1.0uF capacitor at each of the GVDD_x pins.

There is a 220uF bulk capacitor plus a 0.1uF capacitor at each of the PVDD_x pins.

I do have ferrite beads connecting the outputs together.

Schematic is attached.

Running some high temperature testing here.  At room temperature the leads of the motor show a 0.5% duty cycle when the commanded motor speed is zero.  This 0.5% is there to satisfy pg. 11 of the datasheet requirement to keep the bootstrap caps charged.  Once the oven is ramped up to ~75 degC and allowed to soak for several hours, we checked the motor terminals again and the 0.5% duty cycle is no longer present.  Any ideas?

Hi Steve,

I will address the last two posts here. Thanks for the schematics. I didn't see any thing of concern there.

Let's ignore the nfault = 0 for now.

Since you are using CBC current limit, are you toggling both PWM_A and PWM_B during each cycle? If not, this could be the reason for the duty cycle to disappear. Please refer to the first paragraph on the right side of page 14 for details (it should say modes 1, 3, 4; mode 2 is latched oc).

When the commanded motor speed is zero, what do you want the outputs to be; both high, both low, or both floating? If both low or both floating, I don't think you need the 0.5% duty cycle. As you noted this is to charge the bootstrap caps.

By setting the outputs low, the bootstrap cap is charged until the output is set high.  If the outputs are floating, then the output should first be set low to charge the bootstrap cap. Then it can be operated as usual.