DRV8832: Fault pin doesn'r assert when the motor stalls.

Wayne Wang20

Part Number: DRV8832
Other Parts Discussed in Thread: TEST2,

Hi team,

My customer is using DRV8832. The scheamtic is as below.

F_VCC = 3.6V

Please note that R33 is not soldered so VSET=VREF=1.285V and the desired output voltage=Vout=1.285*4=5.14V which is larger than F_VCC. So DRV8832 will operate in 100% duty cycle which makes actual output voltage=F_VCC=3.6V.

Motor spec：3.6V rated voltage，stall current=330mA

We found below different behavior on Fault pin：

Test1：set Rsense=1ohm，so current limit=200mA. When the motor stalls, Isense pin gets to 200mV limit and the fault pin can assert.

Blue=Isense pin voltage

Yellow=Fault pin voltage

Test2：set Rsense=0.75ohm，so current limit=266mA. When the motor stalls, Isense pin gets to 200mV limit but the fault pin didn't assert.

Blue=Isense pin voltage

Yellow=Fault pin voltage

Could you please help analyze why fault pin cannot assert when we set Rsense to 0.75ohm?

Best regards,

Wayne

over 3 years ago

0 Wang5577 over 3 years ago

TI__Guru 56650 points

Wayne,

On the schematic, the current sense resistor 2.4ohm. But, it should be under 1ohm. Would you change the sense resistor to 1ohm?

0 Wayne Wang20 over 3 years ago in reply to Wang5577

TI__Expert 4360 points

Hi,

Please ignore the Rsense value in the schematic. Like I mentioned, in test 1, we tried Rsense=1ohm and in test 2, we tried Rsense=0.75ohm.

The issue is Fault pin cannot assert in test2 but it works in test1.

Best regards，

Wayne

0 Wayne Wang20 over 3 years ago in reply to Wang5577

TI__Expert 4360 points

Hi Li,

Could you help advise the next step plan to debug? Can you help try the same test with DRV8832EVM and a similar motor to customer? Thanks.

Best regards,

Wayne

0 Wang5577 over 3 years ago in reply to Wayne Wang20

TI__Guru 56650 points

Wayne,

Let me check our lab tomorrow morning to see I can find a DRV8832EVM.

0 Wang5577 over 3 years ago in reply to Wang5577

TI__Guru 56650 points

Wayne,

I duplicated this issue with a low input voltage. When the input voltage is very close to the under voltage lock off voltage, the issue can be duplicated.

Would you reduce the input voltage drop from the input wires or increase the input voltage a little bit? And then, we can check the issue goes away or not.

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DRV8832: Fault pin doesn'r assert when the motor stalls.