Tool/software:
Hello Team,
can you please help my customer:
We use the DRV8872-Q1 to control a DC motor. It was used as a replacement because the original one from infineon went EOL.
During tests I noticed something strange that I would not have expected.
When I block the motor and then give the command to drive, pin 5 (VCC) burns out. The corner of the housing looks blown open, and a piece of pin 5 has actually melted away.
I looked at pin 4 (/FAULT), but it remains constant at 3.3V.
My assumption was that the internal protection mechanisms take effect in the event of an overload and pin 4 reports an error. Or in the worst case there is something on pin6 or pin8, i.e. on the outputs.
The motor current jumps to just under 4A and then drops. However, I cannot determine the exact sequence when the IC dies.
Here is the circuit diagram in which only the motor driver has been replaced.
I have also soldered an additional 220µ electrolytic capacitor across the IC's supply pins, because the data sheet mentions a bulk capacitor, but unfortunately that didn't help either.
The offpages on the right go directly to the plug. There are no more components hanging in the branch.
The driver looks exactly like the picture in this thread.
I measured the pin to ground resistances on a defective and good IC on the LP:
|
|
Defect /R |
Good /R |
|
Pin1-GND |
0,2 |
0,2 |
|
Pin2-GND |
99k |
99k |
|
Pin3-GND |
99k |
99k |
|
Pin4-GND |
3,5k |
3,5k |
|
Pin5-GND |
- |
217k |
|
Pin6-GND |
0,2 |
4,1M |
|
Pin7-GND |
0,2 |
0,2 |
|
Pin8-GND |
0,2 |
1M |
-> The two outputs (PIN 6 & 8) have a termination to GND (Note: Pin 7 (ISEN) is connected directly to GND)
In1 and IN2 were as follows before the defect:
Idle state: Brake IN1=1, IN2=1
Motor was stopped
Motor start with IN1 =0, IN2 = 1
The two In pins are controlled statically, i.e. no PWM.
I looked at the VCC current, but unfortunately it was not saved correctly on an old oscilloscope. No abnormalities were visible, except that this IC had another defect. PIN 5 has not melted away, the motor continues to turn, with periodic short interruptions. The IC reaches approx. 140°C, then pauses and restarts after approx. 200ms. The driver does this even though it is not activated (IN1 and IN2 should both be set to 1).
Thanks
Jan
