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LM5170-Q1: Inductor current ripple ratio limits?

Jamie Shaffer1
Prodigy 220 points
Part Number: LM5170-Q1

The title says it all. Is there a limit on the allowable inductor current ripple? Could it tolerate, say, 200% Ipk-pk?

  • +1
    TI__Guru 68395 points

    Hi Jamie,

    Theoretically there is no such absolute ripple current limit.  We usually recommend to operate the circuit is CCM at full load.  At 200% ripple your circuit is always operating in DCM and the efficiency would be sacrifices due to increased RMS current.  In our EVM, the ripple current is about 80%, which means CCM down to about 40% load.   I would recommend your ripple current not exceeding 100%.

    In addition, you need to make sure the circuit would not trigger the peak current limit programmed by IPK.  

    Thanks,

    Youhao Xi, Applications. 

  • 0 in reply to Youhao Xi
    Prodigy 220 points

    Hi Youhao,

    I am attempting to program "Borderline Conduction Mode" or BCM. In this technique, the inductor current ramps from 0 to 2*Iavg (that is 200% ripple, if I am using the right terms). This technique has been proposed to allow ZCS and should result in improved efficiency. It also requires variable frequency operation, which is a question for a different thread.

    That being said, if the device can tolerate very large current transients, assuming they stay within the bounds of the Ideal Diode and Ipk limit features, this should perform BCM well in my application.