DRV8231: voltage drop, engine not mooving

Hello Pablo,

I'm using the engine to moove a slide, the sequence is as bellow : 

- 1.5s with IN1=0 and IN2=1  (opening the slide)

-  standby mode with IN1=IN2=1 durantion can vary but never less than 10s.

- 1.5s with IN1=1 and IN2=0  (closing the slide)

- Again standby mode.

I've tried to remove C17, result is the same.

Please find bellow some screenshots, I'm measuring the signal between OUT1 and OUT2.

- with no engine :  all good, i've got 6V and zooming on the curve I've got 100mV triggers 

- with the engine i've got the following signals, first curve is the global view and the 2nd is zoomed signal is triggering from +/-6V :   

Let me know if this helps you... to help me

regards

Bruno

Hi Bruno,

Thank you for providing the information.

What type of motor are you using? is it possible to provide the datasheet? 

Can you zoom in more on the waveform?  I want to see what what those pulses look like.

Based on the information you have shared, it is propable that this is an overcurrent fault. The stall current of your motor is 3A and the OCP limit of this driver is 3.7A peak. If the current is going above 3.7A due to transient spikes in the current, OCP will be flagged and the outputs disable for around 3ms before re-enabling the outputs again. Is it possible to measure the motor current with a current probe?

Regards,

Pablo armet

Bruno Henriques said:

With Vm = 6VDC, when I pull down one of the INx pins when the engine is not connected i've got on the out1 / out2 +/-6VDC so all good.

Hi,

The input INx are already pulled down internally, so if one input is pulled down externally then what is the voltage on the other input? Why not state the input voltage more clearly?

And what is the voltage on the output? +/- 6v? There is no negative voltage on the output!!!

Bruno Henriques said:

I'm measuring the signal between OUT1 and OUT2.

How do you measure the signal between out1 and out2 -- using 2 probes or just one probe and its ground clip? Why not measure each output to GND?

There is too much guessing in reading this question.

Brian

Hi Pablo 

unfortunatly i do not have any current probe, but wih the pike at startup is not above 3A ( spike detector on my meter).

i've got the following signal every 2.4ms : the first pulse is 264us wide, the 3 others spaced of 80us 

Hi Brian,

In fact if there is an internal pull down and i'm having an external pull up this can cause an issue, in fact measuring on IN1 and IN2 i've got 3.3V or GND according to MCu command.

I've measured the output voltage with a DC Voltmeter connected arbitrary between OUt1 and Out2, that is why i measure +6V when engine mooving on one direction and -6V when moving on the other direction, measuring each output ground referenced is also a solution.

Bruno

Bruno Henriques said:

With Vm = 6VDC, when I pull down one of the INx pins when the engine is not connected i've got on the out1 / out2 +/-6VDC so all good.

But when I connect the engine, the voltage drops to approximately 0.5V and the engine is not mooving, i've tried with a smaller engine and it works but voltage to the engine is arround 3V.

Without the motor connected to the output pins, the output voltage is a floating value and it could be 6v floating even if the driver is disable.

I suggest to drive IN1 with 50% pwm with IN2=0v,  and capture the scope waveforms of  IN1, out1 and out2 with motor connected.

Brian

Brian,

Brian Dang said:

I suggest to drive IN1 with 50% pwm with IN2=0v,  and capture the scope waveforms of  IN1, out1 and out2 with motor connected.

This is possible but this device has an autosleep function (device goes to sleep after 1ms when IN1=IN2=0V). The device needs to see at least one of the input HIGH for longer than twake (250µs) in order to be active. The proper wake up procedure is as follows:

1. Apply supply voltage
2. Set one of the inputs HIGH for longer than 250µs
3. set IN1=50% and IN2=0V

Regards,

Pablo Armet

Bruno,

Is there ever a case in your system in which both IN1 and IN2 are logic LOW (0V) for longer than 1ms? If so, the device is going into sleep mode due to the autosleep function mentioned in my previous reply to Brian.

Bruno Henriques said:

With Vm = 6VDC, when I pull down one of the INx pins when the engine is not connected i've got on the out1 / out2 +/-6VDC so all good.

Based on this comment my guess is at least one of the inputs is always HIGH correct?

For testing purposes, I would add a resistive load to remove the motor from the equation and first understand if this behavior is due to the motor itself.

-Pablo

hi Pablo,

We've tried with a 2kHz PWM pulses from 0 to 50% result is the same, the engine is not mooving faster than previously...

Is there a chance that this could com from the fact that we've grounded Isens?

Regards

Bruno

Bruno,

Did you supply the 2kHz right after supplying power to the IC? As I explained before, one of the INx pins NEEDS to be logic HIGH for longer than the wakeup time. Can you try tying one of the INx pins to external logic supply for longer than 1ms and then provide the PWM signal. This will ensure that the driver is in the active state.

Bruno Henriques said:

Is there a chance that this could com from the fact that we've grounded Isens?

Grounding the ISEN pin will only disabled current regulation. However, it is strongly recommended to connect VREF to external VCC supply (which you have done). So I don't think this is the reason. 

Regards,

Pablo Armet