[Motor Driver full H-bridge VNH5050A-E] PWM maximum frequency problem

Robotics and electronics discussion Electronics
1

I had a problem with this component VNH5050A and I need your support.ﾠ
My test bench is composed by:

  1. A PCB board (created by myself), where I solder the VNH5050 with the same resistors and capacitor shown in the typical application found on datasheet.ﾠ
  2. Input capacitor of 1000 uF on supply voltage.ﾠ
  3. A DC Brushed Motor.
  4. Signal generator.
  5. Oscilloscope.
  6. DC Power Supply (Work condition 10V without current limitation; Max 50V, 30A).ﾠ

I had this problem with two different DC Brushed Motors (motor A: max operate at 16V, 5 A; motor B: works max 16V, 20A) without load.
The configuration of VNH5050 is: PWM [0-5]V, INA connect to 5 V, INB connect to GND, ENA_DIAGA and ENB_DIAGB pull-up with 3.3 kOhm to 5V.ﾠ
I read from datasheet that I could work up to 20 kHz PWM Frequency but when I reach 5 kHz of PWM Frequency I see on oscilloscope the output does not follow the input PWM signal. The output jumps some PWMs input, for more details I attach the images of the oscilloscope for the two motor.ﾠ

Legend of oscilloscope’s signals: Channel 1 (yellow) VoutB (voltage between outB and GND), Channel 2 (green) PWM input, Channel 3 (blue) VoutA (voltage between outA and GND), Channel 4 (pink) Current sense pin after filter (copy from datasheet).ﾠ

I also try the configuration with 1kHz of PWM and I see the correct behaviour of the component. I attach the image for clarity, the signals of oscilloscope are the same of previous attempt.

PWM_1kHz
PWM_1kHz800×503 24.2 KB
PWM_5kHz
PWM_5kHz800×503 21.1 KB

2

Hello.

We do not do anything with that particular driver, but I did check out the datasheet and verified that it should be able to operate at up to 20 kHz, so I am not sure what could be causing that behavior. Is it possible that you are accidentally confusing the INA and PWM pins? The switching time for the INx pins is much slower than for the PWM pin, so it seems like that kind of mistake could produce the results you are seeing.

-Patrick

3

Hello Patrick,
I check the pinout and wires connections but I not found any problems about INx/PWM or other pins.
Thanks for the kind support.

–Andrea–