DRV8840: DRV8840 stops and require reset

tds

Prodigy 90 points

Part Number: DRV8840

Support Path: /Product/Development and troubleshooting/

The DRV8840 is used with a PWM (Approx 8kHz) connected to Enable input and Phase input is used for direction.

Sleep = high

Decay = low

I0, I1, I2, I3 and I4 are all high

Reset is low during start up, and then high.

Current limit is set to approx. 3A.

VM = 9V.

A 4 ohm torque motor is connected and is running very well from 0% to 100% PWM (both way). But if the load is disconnect when the PWM is between 10% and 100% the PWM stop !, and DRV8840 require a reset to start up again.

In the data sheet it is stated that OCP can give this state, but in this case is the current below this limit.

Seen this problem before ?

over 8 years ago

0 Rick Duncan over 8 years ago

TI__Guru** 114905 points

Hi tds,

Are you monitoring the nFAULT pin? Assuming the nFAULT pin asserts, please look at the current prior to the nFAULT pin asserting. Zoom in to 2 to 5us/division. Can you provide a scope capture of the current, nFAULT, and nSLEEP prior to nFAULT asserting?

How is nSLEEP connected? Is it pulled up to a logic high through a resistor? If so, what is the value of the resistor.

0 tds over 8 years ago in reply to Rick Duncan

Prodigy 90 points

Thanks for your information.

When I start measuring the current I observe a lot of noise, the noise is from the spike generated when releasing an inductive load.

Scope picture:

The yellow curve is the nFault signal, and the pink curve is the current measured above the Isene resistor (0.1 ohm).

100mV gives 1A.

The nReset and nSleep is high all the time.

When I connect a 47nF cap between OUT1 and OUT2 the problem was solved.

It could noise from the release pulse in some way is transferred into the circuit and give the problem. (The current generated from this pulse should not be more than 1A max).

Best regards

Tor Dag