soft start with ADuM3190 & difference between EAOUT & EAOUT2 transient performance

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?

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  • 0
    •  Analog Employees 
    on Dec 9, 2019 6:36 AM

    Hi:

    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. 

    Regards

    Chris 

Reply
  • 0
    •  Analog Employees 
    on Dec 9, 2019 6:36 AM

    Hi:

    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. 

    Regards

    Chris 

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