LM629 PIN 13(PWM MAG) AND PIN 11(PWM SIGN) Issues

Hi Team,

The customer is using LM629M-6.

 PIN 13(PWM MAG) can output PWM and PIN 11(PWM SIGN) is a low level occasionally when the board is power on without any initialization. The PWM for  PIN 13(PWM MAG) is about 3%.  The malfunction has  appeared on several  boards. Once this malfunction occurs, the motor rotates fast. 

The attached are the schematic and the waveform for the malfunction. VCC is 5V  and fCLK is 6MHZ.

What is the reason? How to solve the issue?

Thanks,

Best Regards,