L6235 Motor jumps to Max above certain reference voltage

[matthias239955_stm1_st]

Posted on August 01, 2016 at 10:17

Right now I am working with the evaluation board EVAL6235N and I adapted the L6235PD to it and changed the Shunts to 0,167 Ohms. The motor is a fan from Micronel which has a maximum average current of 1,5A when freeblowing.

The reference voltage is set from outside and the whole setup works as it should in the lower area.

There are certain problems with regulating the device: When I use the reference voltage to drive the motor, at one point (approx.. 1,2Amps) it�s speeding up to maximum immediately, so there is no chance to reach defined values between 1,2A and 1,5A. Afterwards I have a big hysteresis to lower the speed.

To avoid that I set the reference voltage above 5,6Amps and try to use a PWM on the Enable-Pin of the device � now the internal limiting Diag-Pin pulls down the enable but the motor runs stable and regulated under all conditions even when the input is very sensitive to different PWM-frequencies. When I set the reference voltage to 5Amps the Diag-Pin stays fine but again the motor is jumping to maximum above a certain current

like in the first case.

#bldc #l6235 #l6235pd

[Hari Prasad Gokul Ravichandran]

Posted on January 16, 2018 at 08:11

Poli.Enrico

#l6235

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#bldc

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I have the same observation regarding speed control using the L6235 VRef Input.

It is extremely difficult to establish a user-friendly range on VRef Input to get a full scale speed control. PWM switching the FWD/REV Input is one workaround, but the switching causes the motor to hum and does not feel like an elegant solution for speed control.

How can one best use the VRef pin for fine speed control of the motor? What is the relationship of the VRef input, motor speed and the current shunt resistor? I have fine control over the signal to VRef input (tried it both ways: analog as well as PWM DAC). But this does not translate to fine control of the motor speeds, especially at low currents. While varying the value of the shunt resistor may help provide a better control range over Vref, I am not sure that is the best way to go ahead either.

Looking forward to a discussion regarding this.

[dgrimes]

​I too would like information on the Vref input, I have had a support request open for nearly one month and no one has responded. It makes you wonder is this chip even being used?