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LM3488Q-Q1: LM3488Q-Q1

Csongor Meszaros
Prodigy 30 points
Part Number: LM3488Q-Q1
Other Parts Discussed in Thread: LM3488, LM5155, LM5157

Dear TI support,

I would like to ask you about the LM3488 in Sepic configuration:

Vin = 6V to 18V

Vout=13.5V

Iout_max = 0.9A

fsw = 220kHz

L = 15uH

Cout = 100uF

Feedback loop bandwidth = 12kHz

By running an automated measurement setup (Vin and Iout parameters are swept), the below results are generated:

This is a very slow measurement (Vin is set, 1 sec waiting time, Iout is set, 1 sec waiting time, Vout read).

My question is regarding the output voltage elevation at no-load/minimum load:

1) could you please confirm this is a normal behavior of this IC?

2) is this coming from the Vcomp behavior? (snippet from datasheet)

Thanks in advance,

Kind regards,
Csongor

  • 0
    TI__Genius 11405 points

    Hi Csongor,

    I believe this is due to the Over voltage protection.

    You can find from datasheet 7.1 Overview:

    Under extremely light load or no-load conditions, the energy delivered to the output capacitor when the external MOSFET is on during the blank-out time is more than what is delivered to the load. An over-voltage comparator inside the LM3488 prevents the output voltage from rising under these conditions. The over-voltage comparator senses the feedback (FB pin) voltage and resets the RS latch under these conditions. The latch remains in reset state till the output decays to the nominal value.

    Best Regards,

    Feng Ji

  • 0 in reply to Feng Ji
    Prodigy 30 points

    Thanks for the fast response. 

    Then could you confirm that the LM3488 can not provide better regulation in light load conditions?

    Best regards,
    Csongor

  • 0 in reply to Csongor Meszaros
    TI__Genius 11405 points

    Hi Csongor,

    We cannot change this feature.

    If possible, you may use LM5155 or LM5157. Pulse skipping is utilized at light load, thus the regulation at light load will be good.

    Best Regards,

    Feng Ji