View Full Version : SpinStamp and the lm2937?

11-17-2011, 02:29 PM
Can the spinstamp supply a 3.3 volt lm2937 through its VDD output.
Maybe, with a resistor between them, the 500 mA capable lm2937 would not overdraw the 400 mA current limit of the VDD pin!

Mike Green
11-17-2011, 02:57 PM
"Can a SpinStamp ... VDD output?" ... Yes, but

The SpinStamp has a LM2937-5.0 regulator connected between Vin and Vcc (it's not called Vdd on the schematic). There's then an LM2937-3.3 regulator connected between Vcc and Vdd (the strictly internal 3.3V connection).

You can connect another LM2937-3.3 regulator from Vcc to some other circuitry and it will work the same way as the internal one. The issue is ... what is the total current drawn from the 5V regulator? You'll have to figure that out. Remember that none of the LM2937 regulators on the SpinStamp have a heatsink (other than the module itself). The 5V regulator's output current will be limited by the amount of heat it has to dissipate. You'll get the most output by running the SpinStamp off Vin = 6.0V.

Why put a resistor between Vcc and the other LM2937-3.3 regulator?

11-20-2011, 02:44 AM
I intended to run a radio that needs 3.3 V from the added lm2937 and use the 5 volt output of the spin stamp to fuel it. I may be able to fit another 5 v Reg on the board to feed the 3.3, but I thought what the heck. If the draw on the vdd from the spinstamp is ok then I could omit the second regulator.