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I'm going to fabricate my first PIC-like F28027 main board, where I'm going to drive a small motor using TI's DRV8832.
BUT before that, just a quick question: I'm just wondering if it's necessary to put resistors and diodes in between the pins of the F28027 to the DRV8832? I'm caught between two outcomes if I don't put any; whether it might induce erratic behavior due to the motor's spikes OR if I do put diodes/resistors might it render the output current too low?
In case for PICs, the use of diodes and resistors in series are usually desirable for stability when I'm connecting it to a driver. However, I don't know if there are already internal designs in the DRV8832 which takes care of such things.
Hope for your replies soon.
Vortex Electrica Corp.
In reply to Abdul Halim Poh:
You're very welcome, I'm glad to hear everything worked out!
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In reply to Casey Leavitt:
Thank you for your detailed description. You mention that you see pulsed output power on your setup at start-up time. Did you see it at shutdown time too? This is the behavior that I am trying to understand. The power pulsing at motor start-up is not really a problem. I simply do not expect to see it. But the 10s of ms delay between placing the 8832 device inputs into BRAKE configuration and the voltage across the motor terminals pulsing "down to zero" is unfortunate and confusing.
Unfortunately for me, I have already tried tying Isense to GND and that does not change the motor power output of the 8832 device. I intended to mention this in my first post but forgot. It may be that the inrush current through the 12ohm motor coil is sufficient to trigger a thermal shutdown.
When I combine this newly confirmed understanding with the facts that the 8832 power output also lags the input at power shutoff time by 10s of ms and that the Vref voltage is 2.6 V (which is incorrect but probably shouldn't matter) I am hoping/becoming convinced that the device I am using is not functioning correctly. I have been using it for some hours. I suppose I may have damaged it somehow. I will have to get another one and try it to see if the behavior is consistent.
Also, thank you for the reference to the 8837 part. I was aware of it but chose the 8832 because I do want to use the current sense feature in my final design.
In reply to Kerry Ober:
I do not see any pulsing when I go into the BRAKE configuration, but I do see the voltage ramp down similar to how you described when I go into the COAST configuration. I've grabbed a couple of oscilloscope waveforms to show you what I see on my device. These traces are all referenced to the GND of the power supply. You mentioned measuring the "voltage across the motor terminals" which may look different.
Similar to what you see, when I go from "off" to "forward" by bringing IN1 high, I get the pulsing due to inrush current.
When I put the device in BRAKE mode by bringing IN2 high as well, I don't see any pulsing on either side of the H-bridge.
If instead I put the device in COAST by bringing IN1 back low, I see this waveform as the voltage decays to 0. With the particular motor I was using, it took >1s for the voltage to settle down to 0 completely. This is the expected operation of the device since when put into COAST, the H-bridge is put into Hi-Z mode rather than shorting the motor terminals as in Brake mode.
I don't think the motor you are using has enough resistance to cause a thermal shutdown since this would disable the device completely until the temperature drops to a safe level. Do you see this kind of behavior in startup?
Based on the information you have provided I would agree that your device is most likely damaged. The Vref output of 2.6V is above what is specified as the absolute maximum by the datasheet - this is a sign that the internal reference circuitry has suffered a failure and I would not trust the rest of the chip to behave exactly correctly if this is the case.
Hope this helps! If you still see this kind of behavior on the next device you test please let me know and I will help you to troubleshoot further.
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