Emiel Schimmel

MM908E626: Current limit Chopping on FGEN

Discussion created by Emiel Schimmel on Jul 15, 2011
Latest reply on Jul 15, 2011 by Emiel Schimmel



I'm programming a MM908E626 controller with;

- M68HC08EY16 microcontroller

- a H-bridge with current limiter settings, controlled via SPI.


I have set the Current Limiter Setting (CLS) at different values.

I have tried different values PWM signals on FGEN. 

I have used different FGEN values but all within the specified recommended settings.



unfortunatly the output of the h-bridge is not re-enabled on every rising FGEN! Therefore the current isn't smoot , not even with a 20Khz pwm on  FGEN !!

Why isn't the output re-enabled ?




how I did applied the specifications in read the datasheet:

The datasheet of the MM908E626 specifies the H-bridge. On page 27 of the datasheet a picture(figure 13. Half-bridge current limitations) explains that:

1. The half-bridge output is disabled when the set current limit is reached.

2. When the current limit did disable the half bridge, a rising edge on the FGEN input would re-enable the output again.


With this information in my mind I programmed a PWM signal from the microcontroller to the FGEN input of 20 Khz, 50uS interval. I did use a scope to verifie that this signal was now present on the FGEN input !! I did use the scope-input 1 to check on different FGEN values and I did use input 2 to measure the h-bridge output. I used the FGEN to trigger the signal.