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LM3478: Load free output ripple issue

user5112180
Prodigy 210 points
Part Number: LM3478
Other Parts Discussed in Thread: LM5022, TPS43060

Hi,

When LM3478 has no load, it enters hopping mode, if output voltage exceed OVP threshold, output will be disabled, which leads to output voltage go down until hit hysteresis bottom voltage. A voltage ripple with 2 votes will be generated. Is there a way to avoid this situation? If not, can I use LM5022 to alleviate? If LM5022 is not going to fix, any other IC works? 

  • 0
    TI__Guru 71445 points
    Hi user5112180,

    Thank you for considering our devices. What you are talking about is the min duty cycle issue in non-synchronous boost. At no load or very light load, the PWM controller can only has either no duty or a certain min duty (refer to the datasheet page 5, the row of Tmin(on)). The LM5022 would behave the same. There are three options to resolve or diminish this issue.

    (1) Increase output capacitors;
    (2) Add some dummy load or use a Zener slight above your ourput voltage setting;
    (3) Change to a synchronous boost controller like the TPS43060 or LM25122. In forced PWM (or CCM), both controllers would help you eliminate such issue.

    Thanks,
    Youhao Xi, System and Applications Engineering, APP-BMC-BCS, TI