TPS54140A: Vout Ripple in case of a small Load (pulse skip mode)

Toshiya Asai

Part Number: TPS54140A
Other Parts Discussed in Thread: TPS54140

The output of TPS54140A 24->5V circuit shows a large Vout ripple in case of No load.

If there exists a load resister for 20mA current , the above ripple disappears.

The follows are the comparison when I changed the inductance value. The waveform of 4.7uH case is clean, but both 33uH and 100uH cases have 0.2Vp-p ripple (cycle time is greater than 20ms).

I want to know the reason of ripple, because my application needs a small current load ( less than 50mA ) .

Why does the ripple disappear by using a small inductance ?

over 5 years ago

0 Robert Blattner over 5 years ago

TI__Expert 6215 points

Hello user4778976,

When lightly loaded, the TPS54140 provides pulses that are the shorter of:

1) The time it takes inductor current reaches the minimum peak current defined in the feature description portion of the datasheet as 50 mA.
2) The end of the clock cycle.

As the inductor’s value is increased, it takes longer for inductor current to reach 50 mA so more charge is transferred to the output capacitor during each cycle. More charge per cycle with a fixed output capacitance equates to greater output ripple.

Regards, Robert

0 Toshiya Asai over 5 years ago in reply to Robert Blattner

Prodigy 180 points

Please refer the thread below regarding this matter.
"TPS54140A: Ripple in very small load operation"
I added the waveforms in the above new thread, so please give me a feedback in the new thread.

0 Robert Blattner over 5 years ago in reply to Toshiya Asai

TI__Expert 6215 points

I will continue on new thread.

Regards, Robert

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TPS54140A: Vout Ripple in case of a small Load (pulse skip mode)