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LM5017ISOEVAL: AN-2204 LM5017 Isolated Supply Evaluation Board

user3881732
Prodigy 30 points
Part Number: LM5017ISOEVAL
Other Parts Discussed in Thread: LM5017

HELLO,

           There is one question absout TI AN-2204，why add a C9 capacitor to the reference design，C9 capacitor parameter is 2200pf/2000V. What does c9 do, and how is the voltage and capacitance of C9 designed in the fly-buck？

           and the second question is about  COT type-3 ripple circuit，Calculation methods are different for different design documents（SNVA874、ZHCA611、LM5017）, the calculation results are also different. Which calculation method is your most recommended. The Cr=3300pf，Cac=100nF in the LM5017 spec, how the parameters are considered？

           thank you

  • 0
    TI__Expert 3835 points

    Hi Users,

    Due to high di/dt from the ground loops there is alot of common noise that causes EMI issues in systems. This capacitor is optional is not required for converter functionality. 

    Can you highlight which equations are different between the guides.

    Regards,

    Ethan

  • 0 in reply to Ethan T
    Prodigy 30 points

    1. I am still confused , C9 capacitor parameter  was set to  2200pf/2000V , why do we choose 2000v ? can we use 100v ?

    2. Below three calculation methods are different , which one do you suggest ? and why ? 

    really apprecite it if you could help .

  • 0 in reply to user3881732
    TI__Expert 3835 points

    Hi User,

    Most isolated design has >1kV isolation required between grounds thus requirement for high voltage capacitors.

    I would suggest using the LM5017 datasheet equation. I am familiar with the equations on SNVA874 and found simplifications similar the one on the LM5017 on other device datasheet. 

    Regards,

    Ethan