DRV8873: HPWPR

Dears:

I hope you can help me solve the problem. Thank you.

1. During the test, the chip was always broken occasionally and could not be used again. Please help me to analyze whether there was a problem in the peripheral circuit design.

2、During the test, it was detected that the surface temperature of the motor drive chip reached 91℃. Is the temperature inside the chip already overheated? And cause chip damage

3、pwm_out1 is the control PWM output by MCU, and pwm_back is the PWM returned by the motor drive chip. In the test process, when pwm_out1 is 100% duty cycle, the maximum load current is occasionally 5A, generally about 4A. However, the overcurrent protection threshold is set to 6A. In this case, the nfault2 foot is pulled down by about 70ms in a cycle.This will not damage the chip because of overcurrent protection too many times.

Cherry Zhou：

Hi we have received your questions and are checking the problem. If there is anything new I will follow up to you asap. Thanks!

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Cherry Zhou：

Jingjing Li 说：1. During the test, the chip was always broken occasionally and could not be used again. Please help me to analyze whether there was a problem in the peripheral circuit design.

Can you provide more detail. How was the test performed? Can you provide waveform captures to help with my analysis.

Jingjing Li 说：2、During the test, it was detected that the surface temperature of the motor drive chip reached 91℃. Is the temperature inside the chip already overheated? And cause chip damage

91C is well below the TSD rating for this device so there should not be any damage to the IC caused by the high temperature.

Jingjing Li 说：3、pwm_out1 is the control PWM output by MCU, and pwm_back is the PWM returned by the motor drive chip. In the test process, when pwm_out1 is 100% duty cycle, the maximum load current is occasionally 5A, generally about 4A. However, the overcurrent protection threshold is set to 6A. In this case, the nfault2 foot is pulled down by about 70ms in a cycle.This will not damage the chip because of overcurrent protection too many times.

Can you provide a scope shot of the nFAULT and motor current when nFAULT drops low? If you set the OCP mode to automatic retry, the device will re-enable the driver after sometime and disable it again after the deglitch time if the OCP fault condition persists. If this repeats multiple times, the device should not be damaged.

Has this issue been observed in more than one IC?

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Jingjing Li：

test pwmwave.docx

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Jingjing Li：

This is the case with more than one IC。

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Cherry Zhou：

Thanks for your info, and I have feedback it to the engineer, if there is any updates I will follow up asap.

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Cherry Zhou：

Looking at the waveforms, this seems to be an overtemperature shutdown fault happening. You can see from the waveforms that as the current is lowered, it takes longer for the nFAULT to go LOW. Lowering the current will cause a slower temperature rise. The cause of the high temperature can be due to poor thermal on the PCB or the GND PAD not soldered properly. Please compare your layout to the recommended guidelines specified in this app-note. If you'll like, we can also review your layout.

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Jingjing Li：

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Cherry Zhou：

Thanks for your image, I will feedback it to the engineer and if there is any new info, I will update to you asap.

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Cherry Zhou：

Hi, is this a 4 layer board? If it is only a two layer board, we think the thermal performance of this board will not be good. You need to have enough GND copper connecting to the GND thermal PAD of the DRV8873. Also, if there is enough space on the bottom layer, there should enough a large area of GND underneath the thermal GND PAD of the driver to help with thermal dissipation. If 4-layer board, having a dedicated GND layer will drastically improve the thermal performance of the board.

We strongly recommend re-designing the board if possible to improve the thermals. Specially since you are driving high currents (up to 5-A at maximum operation). Make sure to follow the guidelines on the app-note we linked in previous reply.

Hope this is helpful for you.