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L6235 Motor jumps to Max above certain reference voltage

Question asked by Entwickler on Aug 1, 2016
Latest reply on Jan 16, 2018 by Hari Prasad Gokul Ravichandran

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.