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Fast decay option for G2 driver


#1

I have already used G2 driver (24V13) with a coreless motor (very low inductance).
After solving some formula, I have created current control method using PWM but it can be used only with fast decay driver. I think that the gate driver IC in G2 driver should be able to set into fast decay, so I suggest you bring that pin out so the user can set decay mode whatever they want. If it is possible, I would like to have a driver which is fast decay when PWM is low, but slow decay when current limit is reached.
Thanks.


#3

Hi, zerozaber.

Thanks for your suggestion. For this particular product, it would not just be a matter of bringing out a pin to allow fast decay, but we would like to understand what you are trying to do so that we can consider it for future products. Could you tell us why you prefer fast decay operation for your application? (We usually prefer slow decay because it gives a more linear relationship between duty cycle and motor speed.)

The G2 driver supports locked-antiphase operation, which effectively results in the maximum possible fast decay; if that is an option for you, it might give you the behavior you’re looking for.

Kevin


#4

It does not matter if I use it with an iron core motor (high inductance). However, with coreless motor, locked anti-phase heat the motor a lot (even with 100kHz frequency). I have used 24V coreless motor with 24V supply with 100kHz locked-antiphase, and the result is that current rise up to 2A and fall to -2A. My motor is rated at 5A, but its inductance is approximately 24uH, not in mH scale.
The main reason I want fast decay is to use current prediction formula to control current of a coreless motor by controlling PWM duty cycle. The motor has optical encoder mount at the rear, so I gets its speed. To control the current, I made it such that at the ON time of PWM, current rise up, and when PWM is OFF, the current must fall down to zero. The key is fall down rate, as current must fall down to zero before next ON cycle comes. Note that current graph in every PWM cycle will looks like distorted triangular.
Accuracy of this current control method is related to accuracy of measured speed, or back EMF. With a slow decay driver, only back EMF and resistance are used in decreasing current. without high accuracy back EMF measuring, accuracy of decay time is very low. But with fast decay, there is additional decay voltage from supply. Note that my project focus on controlling motor torque by controlling current. I have successfully use this formula with fast decay driver, at 100kHz, but that driver max current limit is only 5A, So I can only use theoretically maximum current at 2.5A.

Also, a slow decay driver can not sense current when it is braking, as the current won’t go through current sense resistor, So current limit mechanism won’t work.

Edit: After checking IC datasheet, It seems like your gate driver IC does not support fast decay. I would like to know if you have plan to develop fast decay driver soon.


#5

What is the driver that you have successfully used?

You might consider one of the “CS” versions of our first-generation high-power motor drivers (18v25 CS, 24v23 CS, 36v20 CS). These drivers support drive-coast operation, in which the motor outputs are disconnected during the inactive portion of the PWM cycle. They also have an integrated ACS714 current sensor (the same one used on this board), which might be useful to you as it should offer a more accurate reading of the motor current than the G2 drivers can provide.

We do not have plans for making other similar drivers any time soon. However, if you have a high-volume requirement and want to look into a customized version of one of our existing drivers, please contact us directly with your target volumes, prices, and schedule.

Kevin