I am using the ADuM3190 in a DC-DC converter as isolation errror ampliifer.
How can i achieve soft-start using the EAOUT pin of the ADuM3190? I tired using RC at the +IN pin. But until the VDD2 reaches 3V the output is oscillating and sometimes shooting up.
If i use EAOUT2 pin, the soft-start of the PWM IC is working, but from 3V until whic point there is no soft-start.
How can i achieve soft-start from 0V to the full output voltage.
Why is the performance different for the two outputs?
The load & input transient performance for the two outputs is also different with the same compensation circuit.
How can i achieve the soft-start without affecting stability?
Or would you recommend any other equivalent IC which will provide this function?
usually the soft start is realized in the controller IC. A specific circuit will generate PWM to initialize switching so that all the power rail could be established. Then feedback loop starts to work and FB signal will take charge to generate PWM signal, DCDC's output voltage will follow the reference voltage.
The ramp up of reference could be realized by adding RC between REFOUT and +IN, but this only works when the control loop is already closed.
Another thing is that once VDD1 and VDD2 are ready, the isolated amplifier starts to work, we will see a transient on EAout and EAout2. there is no soft start control on this transient, need external circuit between EAout/EAout2 and FB of controller IC to smooth this process.
Thank you for the response & suggestions.
So are you saying that the IC cannot provide a smooth turn on with a pwm ic in a dc-dc converter?what circuit are you recommending to smoothen the transition?
We have used another IC ADP1074 in a project. This IC has both open loop soft start as well as closed loop soft start and the transition between the two is also made smooth by making the +IN equal to the voltage at -IN at that instant. We are trying to implement the same using some discrete components in this project as well since it's too late for us to change the design now. Kindly let us know if you have any suggestions for the same.
If this feature is available in any other isolation error amplifier IC please suggest. This should have been mentioned in the IC datasheet so we would be prepared to tackle this problem or atleast have the option of using some other IC.