> >The LM2941 has a regrettably high quiescent current in shut down mode.
>
> I don't see it specified. It isn't the horrible regular Iq is it? 8-(
> It's a lateral-PNP type that draws a LOT of current when Vin-Vout gets
> small and at high output currents.

The datasheet in the 1993 NatSemi Power IC's databook that I have has a
diagram at the very end showing a pullup resistor on the on/off enable line
(low = on, high = off).
A note says "To assure shutdown, select resistor R3 [the pullup] to
guarantee at least 300 uA of pullup current when S1 is open. Assume 2v at
the on/off pin"

The data sheet proper has a value for On/Off threshold current of 50 uA
typical and 00 uA max at Von/off = 2v and Iout  <= 1 amp. (Clearly Iout =
0ish when it's off but this is preeumably the curremt one is switching off
with this Ion/off current. )

So the answer is

    - at least 300 uA (appnote)
    - typically 50 uA (data sheet)
    - worst case         (data sheet)

Choose one :-)

This is a MUCH worse current drain than the LM2936's always on quiesecent
current of 9 uA tyoical, 15 uA max (at load of 100 uA - lower presumably at
no load current.

Turning the supply off with a FET or even a PNP transistor you should be
able to get off state quiescent current down to leakage levels - certainly
far far far below 1 uA. Cost is 2 transistors max (1 NPN, 1 PNP and 2
resistors)(1 transistor if you use the PIC RA4 pin trick to drive the PNP).



            Russell McMahon

--
http://www.piclist.com hint: PICList Posts must start with ONE topic:
[PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads