lm22677 low temperature problem

riccardo palchetti

Other Parts Discussed in Thread: LM22677

Hi,

I have problem with the Lm22677.

Attached you can find the circuit diagram.

The Vout (C39) reaches 3.8V (rms) with a ripple of 300mV, instead of 3.4V

The rms value for the FB is over the datasheet range (1.45V) with a ripple of 300, instead of 1.304 (maximum data sheet value).mV.

I also tried to change and increase the C39 to 220uF, without a positive result.

Iout required is 3A

0 Frank De Stasi over 10 years ago

The specifications on the data sheet are for D.C. However, the 300mV ripple does sound a little large.

Are you seeing this issue at all temp or only cold ??

In any case the layout is very important for a switcher; if you send us a copy of your PCB layout we will review it for you.

0 riccardo palchetti over 10 years ago in reply to Frank De Stasi

The Vin is a steady 15Vdc.

The problem is that the Vout is not, as it should be, a 3.3Vdc but 3.7V with a ripple of 300mV.

The Vout increases that rms value and the ripple depending on the temperature and the load.

Higher the load, higher the ripple and the rms value on the Vout.

Lower the temperature, higher the ripple and the rms value on the Vout.

Here below a snapshot of V(C42) @ -40°C with a load of 3A.

And also attached the routing (unzip it and open .tgz with a odb viewer)

0 Frank De Stasi over 10 years ago in reply to riccardo palchetti

Please send a pdf of each routing layer, including planes and silk screen of the area where the regulator is located.

Power management forum