Hi M. Sreenivasan,

InnoSwitch3-EP implements a soft-start sequence at startup. At startup, the primary controller is limited to a maximum switching frequency of 25 kHz and peak drain current is limited to 75% of ILIM. After the primary-secondary handshake, the secondary side controller is in charge of the switching cycle request depending on the Feedback (FB) pin voltage and information from the Forward (FWD) pin. All of the control for switching request is done inside the IC. In the case you've given, there is no place for an optocoupler in a flyback design with INN3670C device, except maybe in some designs with PFC which can be enabled/disabled with an external controller and an optocoupler.

I've attached the design guide for InnoSwitch3 Family devices. It also contains information regarding the FB pin circuit for better output regulation. Thank you for using PI Forum.

Hi,

Thank you for your reply, further would like to make some observations as below 

1) Earlier SMPS design was with TOP268EG rating 85W/24V,3.5A

2) End application is for Vending Machine

3) More than 10K SMPS are in the field with TOP268EG without any issue.

4) when there is over load  motor micro-Controller  senses overcurrent (>5A) & switches off the drive,
  during this period SMPS will neither switches off nor goes to hunting mode.

5) But new design (proto type) with InnoSwitch3-EP (INN3670C),during over load SMPS trips & goes to 
  hunting mode, this was observed during "Rotor Lock" test.

6) Also during Start up Motor draws high current (with Soft start for motor drive) 
  the new SMPS trips & does not support for initial overload .

7) the new design was made for Cost/size reduction.

pl suggest us how to meet this requirements with device INN3670C