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January 6, 2012
about 4 years ago
I will add that my method still has a high startup current of about an amp, but for a much shorter period of time than what the provided resistor set delivers.
For those experiencing startup problems with this board I DO NOT recommend using the method posed by “Frustrated” below as this is probably why he is getting bad ripple. I get good performance with my method.
DO NOT FOLLOW THE DATASHEET for setting ouput voltage.
They have this thing set with RF2 at 100k, and I get much faster startup with virtually no current sap if I use 75K, and then ALSO change RF1 to set the output voltage.
Note that I am using 1.5V input, and still get a sort of current sap with input of 1.2, so perhaps at 1.2V input RF2 should be reduced to 50k ohm.
I believe the startup conditions are heavily set by the total resistance in the RF1 - RF2 resistor set. Use a lower resistance there for lower input voltages (I think). The LM2623 recommends RF2 is somewhere between 50k and 100k.
The correct equation is found on the LM2623 datasheet. It is RF1 = RF2*(Vout/1.24 - 1)
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