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ISOM8110: flyback circuit ringing

Adam Torma
Mastermind 45720 points

Part Number: ISOM8110

e2e,

 

I'm using ISOM8110DFHR as drop in replace traditional photo-coupler but the circuit is ringing.  Do we need to make some adjustment on other components?

         

Topology=Flyback DC/DC

Vout=5V

Iout=20A (Full-Load)

fsw=200kHz

 

Case 1: parameterA  using  TLP293(GRL-TPL,

R29=15K

R31=470R

R32=5.1K

R27=2K

R28=5.6K

IC3=AZ431

IC2=5021

R8=330R

C9=0.1uF

Vout=Normal, no Ringing

 

Case2: parameterA using ISOM8110DFHR

R29=15K

R31=470R

R32=5.1K

R27=2K

R28=5.6K

IC3=AZ431

IC2=5021

R8=330R

C9=0.1uF

Vout=Normal @ Iout<4A, Ringing @ Iout>4A

 

Case3: parameterB using ISOM8110DFHR

R29=15K

R31=470R

R32=5.1K

R27=3K

R28=Open

IC3=AZ431

IC2 5021

R8=220R

C9=1uF

Vout=Normal @ Iout<7A, Ringing @ Iout>7A

 

Case4: parameterB using ISOM8110DFHR

R29=15K

R31=470R

R32=5.1K

R27=1K

R28=5.6K

IC3=AZ431

IC2 5021

R8=0R

C9=47pF

Vout=Normal @ Iout<0.4A, Ringing @ Iout>0.4A

 

Output Ringing Waveform:

White=Output Voltage(Case1) @Dynamic Load between Full-Load(20A) and No-Load(0A)

Yellow=Output Voltage(Case3)) @Fixed Load 7A

 

Yellow=Output Voltage(Case4) @Fixed Load 0.4A

 

Thank you,

Adam

 

  • 0
    TI__Guru 57125 points

    Hi Adam,

    Thanks for reaching out. Please allow me to review the inputs and come back to you, thanks.


    Regards,
    Koteshwar Rao

  • 0
    TI__Prodigy 10 points

    Hi Adam,

    Can you please check the operating current through ISOM81XX when Iout is just below 4A in the first case when it is stable? I believe there is very less current flowing through our input side in this case <0.5mA. If that is the case, can you then try to add a leakage path on the input side controller pin COMP to supply? That will force the current to be higher and it can work. 

    When you removed R28, in this case also the current through our opto is forced on a higher side and system is stable till 7A instead of just 4A. Along with removal of R28, if you reduce R27 to lesser value say 1k, it can work for a larger output current.

    Regards,

    Kashyap