LM2937 and LM2940 Trouble

Lutamos

Sooo I bout one LM2937 and two LM2940 from Parallax. Sadly just one of the three work. One LM2940 work but it is installed in to a B.O.E. I am guessing they other two are bad cause the circuit looks so simple. Unless the little metal tab has to touch ground too. That's the only thing different from the other two. I just put them into the breadboard. The tab on the one that is working isn't really touching ground any way. So I am lost and this has happen to me before! with others LM2940s before. So I am lost a little help please.

Thank, you

PJAllen

The tab doesn't have to be connected as long as the GND pin is connected.· Just remember that it is GND.

Using that output capacitor?·

Phil Pilgrim (PhiPi)

The LM2937 can run fine with a 10uF tantalum output cap, but the LM2940 requires at least a 22uF tantalum output cap for stability. A 0.47uF or higher input cap is also recommended.

-Phil

LoopyByteloose

Swaping designs for 780x and LM2940-x will not work. The output capacitor requirements are quite different. With the 780x, 10uf is about the safe maximum limit, while the LM2940-xx has a 22uf minimum operationg limit. I presume the LM2937 is similar issue about capacitors, but read the PDF for specifics.

Why so, the ones you are using are low dropout and use the output capacitor differently to manage low dropout.

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