BLDC Motor (36V 250W) controller using Allegro A3930

Thread Starter

kristapsdreija

Joined Apr 15, 2014
18
Hey, folks!

I'm designing a control system for a 36V 250W BLDC motor driven e-bicycle and I can't get it to move out of its place.
I've made a PCB with the power part of the design as well as an DIP adapter for the A3930, with the circuit happily connected with a breadboard.
The schematic .pdf can be found in the attachment below.
Am I doing something wrong here?

I mean the motor does not turn and the A3930 is dissipating a lot of power (a few Watts).
The fault flags are always at FF1 = '0', FF2 = '0', so it means that either too low of a voltage on the REF pin is present, or a logical fault has occured.
I've tested that the voltage on the REF pin is ~8V, as it should, so it must be a 'logical' issue, but I can not seem to find it!
The internal oscillator is set so that the internal PWM would be 20.2kHz, and I've tried giving it an external PWM using an arduino (30.3kHz, as it should 'override' the frequency on the RC pin).
I've set the dead-time to be at the maximums of 6.3uS.
The voltage on the VDSTH is set to be 2.5V using two 100R resistors.
For sense resistors I've used three 0R1 resistors in parallel, totalling 0.033 ohms.
I've used some Schmidt triggers on the Hall-sensor outputs of the motor and the sensors are working only while turning the motor in one direction (in the direction in which it is 'hard' to turn compared with the other).
The CSOUT pin is varying between 0V and ~3V.
All of the GHx pins are HIGH at ~16V and all of the GLx pins are LOW ar 0V.

The motor himself is a Chinese 8FUN 36V 250W BLDC motor.

Am I missing something here?
Could You please look into my schematic?

The datasheet can be looked up here:
http://www.allegromicro.com/~/media/Files/Datasheets/A3930-1-Datasheet.ashx

Best regards,
Kristaps from Latvia.
 

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MaxHeadRoom

Joined Jul 18, 2013
23,381
The fact that it is a dedicated BLDC ic should I would think make it almost fool proof?
I am not familiar with the IC in question I have only used the PWM ECCP modules on a Picmicro to program DC and BLDC .
Max.
 

Wendy

Joined Mar 24, 2008
22,475
The Completed Projects Forum is for Completed Projects only. It is meant to allow members to show plans for projects they built so other members can duplicate them if desired. Your thread does not belong in this forum, and was moved here.
 

Thread Starter

kristapsdreija

Joined Apr 15, 2014
18
The fact that it is a dedicated BLDC ic should I would think make it almost fool proof?
I am not familiar with the IC in question I have only used the PWM ECCP modules on a Picmicro to program DC and BLDC .
Max.
I thought it as well... Have not got it to working yet, though... maybe someone could help me?
Has anyone ever used the A3930?
 

Roderick Young

Joined Feb 22, 2015
408
I have no experience with that chip, but one thing I wanted to ask was what the calculation was for RGHA (R12) and similar gate resistors. For power switching, 100 ohms is a very high value. If you have an oscilloscope, you could look at the risetime of the signal on the gates of those MOSFETs - it might be slower than you think, and the transistors may be barely turning on. In the data sheet, I think I saw a load of 3300 pF mentioned for the gate drive outputs, suggesting that maybe they connect directly to the MOSFET gates. If you find that the transistors are getting hotter than you expected, that's another clue that you're driving them too weakly.

But I don't think the above is the reason for the fault, unless maybe the chip started to put out some pulses, then gave up when it saw that the rotor was not turning. What you could do if you had an oscilloscope is see if right after RESET (or a start command, or however the chip works), whether any pulses come out, ever, from GHx and GLx.

I'm stumped as to why the chip would get hot when the motor apparently isn't running. Could it be a wiring error? Maybe some output shorted to ground or Vbat?
 

Thread Starter

kristapsdreija

Joined Apr 15, 2014
18
I have no experience with that chip, but one thing I wanted to ask was what the calculation was for RGHA (R12) and similar gate resistors. For power switching, 100 ohms is a very high value. If you have an oscilloscope, you could look at the risetime of the signal on the gates of those MOSFETs - it might be slower than you think, and the transistors may be barely turning on. In the data sheet, I think I saw a load of 3300 pF mentioned for the gate drive outputs, suggesting that maybe they connect directly to the MOSFET gates. If you find that the transistors are getting hotter than you expected, that's another clue that you're driving them too weakly.

But I don't think the above is the reason for the fault, unless maybe the chip started to put out some pulses, then gave up when it saw that the rotor was not turning. What you could do if you had an oscilloscope is see if right after RESET (or a start command, or however the chip works), whether any pulses come out, ever, from GHx and GLx.

I'm stumped as to why the chip would get hot when the motor apparently isn't running. Could it be a wiring error? Maybe some output shorted to ground or Vbat?
Thank you very mucy for your suggestions! I will try to see the output on the oscilloscope as soon as possible!
 
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