LM25149-Q1EVM-2100: output voltage ripple

Mingkang,

Those 1210 capacitors  have ESR and ESL, do the output voltage probe across C32 with the low-inductance GND rings for low inductance.

Also do you have any other scope probes plugged in? Can you remove all other probes and also GND tied to main scope? Just use Probe GND ring.

For efficiency you can expect efficiency variations based on variations in the components, like DCR and RDSON, as well as the heating of the board. The efficiency is taken with very little time for the board to heat up.

Hope this helps,

-Orlando

Mingkang,

Squarewave is usually due to ESL of capacitors or SW node noise coupling into probe.

C32 should have low ESL so if you probed there then I don't know.

The peak to peak is only 10mV which is very low and similar to user-guide peak to peak ripple.

DCR and RDSON can vary from sample to sample, so it can still be due to component variation as well as temperature.

Hope this helps,

-Orlando

Thanks so much for your quick reply! I really appreciate it.

Hello Mingkang,

The ground signal you are measuring is noise pick up on your probe.  C32 is better for testing Vout ripple because it has a lower ESL than the bigger ceramics, 

Hope this helps.

David.

Hello mingkang,

there is slight differences in ESL between a nF capacitor and a uF capacitors, further, the capacitor is furthest distance away from the switch node.  if you just put your probe close to the inductor you will see noise pick up on the probe.  The best capacitor for cleanest measurement is measured across the lowest value COUT that is furthest from VSWITCH.

Hope this helps.

David.

Hello Mingkang,

Please see link below to an article relating output noise on the output of a switching regulator.

Reducing noise on the output of a switching regulator (ti.com)

Hope this helps.

David.