Part Number: DRV8871
Hi,
We have a problem with the DRV8871.
We control the speed of the engine by measuring the back EMF, the generator voltage of the motor.
The firmware then corrects the speed.
For this we let the motor regularly (every 6ms) for 400μs coast. IN1 = 0 IN2 = 0.
We observe that suddenly and sporadically the voltage breaks down. (OUT2 Sporadic Low, Is there a FET in the H-bridge pulling ti GND?)
C1: Pin DRV_OUT1
C2: Pin DRV_OUT2
C3: Back-EMK (Voltage on the net after the 2 diodes, at 20K)
C2: motor current
C1: Pin IN1
C4: Pin IN2
C3: Back-EMK (Voltage on the net after the 2 diodes, at 20K)
C2: Motor current
C1: Pin ILIM
C4: Pin VM
driver circuit
motor connection
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- For regulated driving we use PWM with approx. 30 KHz.
- ILIM at about 500mA
- travel current nom. about 150mA
- Chopper (peak current, defined by ILIM resistor) is only active while start up, shortly thereafter the current decreases.
- trying 100nF above Rilim, no effect
- trying Rilim = 15K. No effect.
- Motor disturbances suppressed. No effect
- motor with similar parameters from other manufacturers shows the same behavior.
- Motor parameters: R = 65 ohms, 260μH (RLC-meter, 1kHZ), nominal voltage 8.5V.
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Best regards, Alen
