DRV8256: HBridge to DC Motor Driven Valve operation affected due to wire length between these two

Rohit Shete

Part Number: DRV8256

Hello
We are using DRV8256E to drive one of the valve (uses DC Motor).
There are 4 such valves in system, all of them driven by above HBridge

Interestingly the valves that are away (physically) from HBridge circuit operate without issues but the ones near HBridge (physical in wiring) do not operate at all

Even when the PWM is provided to the EN pin there is no M+ or M- signal

Above problem disappears when long wire is added between Valve and HBridge outputs

Other way when a series resistor of 300mOhm is added in this case also the problem disappears

Can anybody please explain me what is happening with this HBridge DC Motor driving scenario.

Valve is 24V, 2.4W
PWM and DIR are given from an Automotive ECU

Power supply is benchtop regulated power supply (24V) + DC DC converter (to power 12V ECU)

Thanks in advance.

over 2 years ago

0 Ryan Kehr over 2 years ago

TI__Guru 55605 points

Hello,

Can you please post a schematic and drawing of motor connection if not obvious from the schematic? Are you getting any nFAULT transitions that would indicate a fault more of some sort?

Regards,

Ryan

0 Rohit Shete over 2 years ago in reply to Ryan Kehr

Prodigy 50 points

Hello Ryan,

Thank you for your message.

I am currently using this board that has DRV8256E
https://www.pololu.com/product/4038

The motor connections are done like below:

Yes, there is nFAULT when motor stops moving. This mean overcurrent right?

I learnt from my valve supplier that there is capacitor connected before DC motor in valve. Do you think that causes heavy inrush current that shuts down the DRV8256 and goes in FAULT mode?

Thank you

0 Ryan Kehr over 2 years ago in reply to Rohit Shete

TI__Guru 55605 points

Rohit,

I think that is exactly what is going on! Isolating the capacitance with inductance in the cabling or series resistance would help to avoid this problem as you have discovered.

Regards,

Ryan

0 Rohit Shete over 2 years ago in reply to Ryan Kehr

Prodigy 50 points

Hello Ryan,

Thank you for this clarity.

We added a series 4.7Ohm, 0.5W resistor and problem is resolved.

If you have any calculations on how to select right inductor to be put after HBridge? Do I need to put it on both OUT1 and OUT2 pins?

In this case series resistor will be dropped.

Thank you

+1 Ryan Kehr over 2 years ago in reply to Rohit Shete

TI__Guru 55605 points

Rohit,

Just need one inductor in series with the load. Your wiring inductance is probably in the nanohenries, so a 10-100mH inductor should be more than sufficient to eliminate this probkem.

Regards,

Ryan

0 Rohit Shete over 2 years ago in reply to Ryan Kehr

Prodigy 50 points

Hello Ryan,

Thank you so much for this information.

Currently I have added 4.7Ohm resistor in M+ wire and issue is resolved. I will try with these Inductor solution and will update.

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DRV8256: HBridge to DC Motor Driven Valve operation affected due to wire length between these two