LM20242

Dawid Koba

Other Parts Discussed in Thread: LM20242

Hi,

I am using LM20242 in my current project. While testing it came out that in some cases output voltage is highly oscillating. In effect voltage rises above 4V, while 3V3 is set for digital components, making them consume large amount of current and after some time destroying them from self overheating. What is unexpected, it occures only sometimes when connecting power (not every time). I have already tried changing softstart(C22) and enable(soldering additional capacitor) times, and loop compensation resistor (R19 on schematic). It was helping quite much, but still there are problems around 12V, while at 8V and 16V it works rather good.

Elements that were changed:

C22 -> 1u ceramic
R19 -> 12k
EN capacitor: 100n

In some cases removing input low ESR capacitor (C2, 33uF/20V) helped.

http://images42.fotosik.pl/530/1551bc8fb77357bf.jpg
http://images36.fotosik.pl/244/8d4e6d05d5a4d390.jpg

Thanks for every responce

With Regards

Dawid

over 11 years ago

0 Timothy Hegarty over 11 years ago

TI__Mastermind 49597 points

Hi Dawid,

You can use the LM20242 calculator tool available at http://www.ti.com/tool/lm20242design-calc to determine stability, with particular attention paid to the output capacitor and its ESR.

Please ensure that there is a ceramic input capcitance, e.g. 4.7uF 50V X7R, as described in the LM20242 app note available at http://www.ti.com/tool/lm20242eval. Also, note that the 3.3V zener on the output will likely conduct if the noninal output voltage is set at 3.3V.

Regards,

Tim