DRV8840: DRV8842 noise

My motor is maxon re35: 24V, 0.2mH, 0.6 ohm.

The pcb board is designed almost the same with the datasheet. The nRESET is connected to the mcu with 3.3V voltage. PWM frequency is 30~48kHz.

The motor has "ZZZZ..." noise and the out- and out+ is not stable whatever the duty is (0%~50% all tried). 

What can I do? 

Thanks!

Hi user5902501,

Can you provide scope captures of the input voltages and output voltages? This will help determine how the device is responding to the inputs.

Hi Rick!

Thanks for reply!

The input and output signal are shown in the first figure.

In the second figure, the output PWM frequency blinks from 31kHz to 48kHz and the most time about 31kHz. The motor still has "ZZZZ" noise.

With the same condition, I have tried LMD18200T. The motor has no any noise .

So why and what should I do?

Thanks!

Ziv

Hi user5902501,

I will have to confirm this, but I suspect the PWM input width is too small to consistently propagate from the input to the output. I may not have an answer until early next year.

Have you tried increasing the PWM input width?

The is true for the LMD18200T also, which states the minimum input pulse width (Tpw) is 1us. Some devices may operate at pulse widths less than 1us, while others may not.

hi Rick:

I have tried different PWM duty with input width larger than 1us, typically  larger than 10us. The output looks normal but the motor still has "ZZZ" noise.

With the same test condition, LMD18200 has no noise.

The size of DRV8840/8842 IC is small and a good option for my application. But the noise is undesired.

What can I do further?

Thanks.

Ziv 

Hi Ziv,

Are you using the same PWM frequency for both the DRV8840 and LMD18200?
How are the PWM, Dir, and Brake inputs of the LMD18200 connected?

Would you please provide scope captures of the inputs vs outputs for both the DRV8840 and the LMD18200?