DRV8701EVM: Abrupt switch to sleep mode & Standby temperature

Hi Franz,

one of my customers is testing DRV8701EVM and wants to add an emergency stop. If they implement this by putting the device into sleep mode at very high load would this pose a risk of damaging the circuit? Would this be a risk if this would take place lots of times?

Assuming none of the Absolute maximum ratings are violated, this should not be a risk. When stopping at high loads, the VM may need to be clamped.

They also measured temperatures of the board and saw 48°C on the chip, when in standby at about 37V. Is there a specific reason for the temperature to be elevated and can it be decreased?

There is no reason for this. Sleep current should be in the uA range.
The higher temperature may depend on the configuration.
Is the temperature rise measured on the EVM or the customer PCB?
If the customer PCB, can you send a schematic?
How is the load configured?

One more question: Is there a reason why the EVM is only available with the E version (without coasting) and not the P version (with coasting)?

The DRV8701E is more popular. The DRV8701E can be removed from the EVM and a DRV8701P placed on the EVM.
Most of the GUI will work. The Motor Control section will not operate properly.
Remove the two resistors connect the mcu to the PH and EN pins, and connect a two channel pulse generator to drive the IN1 and IN2 pins. 

Hi Franz,

Have you heard back from your customer?

I am assuming the EVM was used, so there is no need to send a schematic.

I am most interested in how the load is configured.

Hi Rick,

Yes, the EVM was used. Now it's also on the customer board and shows the same temperature.

There was a misunderstanding on my side though. During measurement the DRV wasn't in standby. It was just in standard operation while not driving the motor. So the motor driver was supplied with 37V but didn't receive drive signals. The temperature is not a problem. Anyways it would be interesting to know why that's the case and whether it can be decreased.

Thank you,

Franz

Hi Franz,

Sorry for the delay.

We will investigate and should have an answer by the end of the week.

Please confirm the following assumptions:
The load is configured as shown in the Functional block diagram (one coil to SH1 and one coil to SH2)
The inputs are set as: nSLEEP = hi, EN = low

Hi Franz,

After running a quick lab experiment, the current in the DRV8701 when awake appears to be ~16mA. At 37.1C/W, this would account for approximately 20C rise using Theta jA (16mA * 37V * 34.8 ThetaJA)

Hi Rick,

thank you for the quick support!

Yes, nSLEEP was high and EN low during measurement. Also temperature didn't change when there was no load or a DC motor connected to SH1 and SH2 as load .

According to your experiment and calculation the temperature rise is reasonable then.

The customer also needs to get TÜV certification for the product. Is it possible to get an extended datasheet with detailed block diagrams and information on complexity (total number of transistors and failure rate)? Is there additional information to the general MTBF and FIT numbers?

TÜV is concerned about the probability that the controller sends a stop signal to the DRV8701 and it doesn't react because of internal faults causing the motor to keep on moving. The same question arises for the current measurement. How high is the possibility that the DRV sends the wrong current information to the controller.

Best regards,

Franz