3-phase motor driver (DRV8313) only works for high impedance loads? Simple circuit!

Thread Starter

Elazar

Joined Oct 29, 2019
36
Hi All,

I am experimenting with a simple motor driver circuit, based on the DRV8313 chip, Datasheet

The chip has a built-in overcurrent protection circuit,

PROBLEM DESCRIPTION: The motor driver circuit works as expected ONLY for loads above (about) 8 ohms, if I connect any load less than that the chip stops working (stops supplying voltage to the H- bridges)

NOTE: the current consumption is not the problem, because even if I use PWM and give 0.09 volts to a 4.5-ohm load the driver chip still doesn't work, no meter the voltage supplied to the load.

If the load is less than 8 ohms, the chip doesn't even start to supply any voltage, it acts like it has detected a short circuit.

however, the load I need to work with is a 4.5 ohms motor,

See part of the circuit design:
1619074170188.png

Is anything wrong with this design, that might couse this problem?
 
Last edited:

AlbertHall

Joined Jun 4, 2014
11,506
You are trying to supply 24V to an 8Ω load. That requires a current of 3A. The chip is rated to supply a maximum of 2.5A and that is your problem.
Note that it doesn't matter if you use a low duty cycle as during the ON time you will still be exceeding the chip's curretn limit.
You need to choose a higher rated driver.
 

Thread Starter

Elazar

Joined Oct 29, 2019
36
It makes sense what your saying,

however, I believe that it takes a certain amount of time for the chip to detect an overcurrent situation,
so the question is will a faster PWM clock speed solve the problem, and if yes, what speed will it need to be?

The datasheet states: tOCP Overcurrent protection deglitch time 5 µs
Does that means that it takes 5us for the chip to detect the overcurrent?

1619081867023.png
 

Thread Starter

Elazar

Joined Oct 29, 2019
36
The motor is a Y type, and each winding is 1.8 ohms,
The supply voltage must be 24 volts, but I will use PWM to reduce the voltage to about 2.5 volts (average)

So the PWM speed needs to be more than 200K?
The Arduino chip can't run so fast so I will need a driver that can handle > 13.33A??
This is very expensive and big?
 
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Thread Starter

Elazar

Joined Oct 29, 2019
36
The circuit will need to control a custom-made 3-phase BLDC motor that is designed for an air blower (a simple fan!)
I don't have a datasheet, but it should be simple to drive this motor as it's nothing fancy...
The resistance is 1.8 ohms in all combinations...
I broke one open to see the winding... basically, it's a Y construction...

1619091636149.png
1619091657015.png
 

Thread Starter

Elazar

Joined Oct 29, 2019
36
No, the motor needs much less voltage than 24V,

Just my circuit gets 24V input and I don't prefer to reduce the voltage with a regulator...
because of the cost and size of the PCB... (high current...)

However, I am not sure if I am correct?
what do you think I should do?
 

AlbertHall

Joined Jun 4, 2014
11,506
The problem with the driver circuit is that with a 24V supply, it will apply 24V to the motor coils, even if only for a brief period of time.
I think you should drop the 24V to whatever the motor actually needs. That could be a switch mode device to keep the heat down.
 

Thread Starter

Elazar

Joined Oct 29, 2019
36
The L6234 chip from ST works up to 5 Amps and only haves terminal protection, and does not have over current protection,
See datasheet: Datasheet
so the question is will the L6234 do the job without the need to reduce the input voltage?

Also, maybe we can solve the problem by just placing a current limit resistor on all the PGND (sense pins)?
 
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