From: "Bob Axtell"


> I am interested because I have an LF88 in a current sensitive app, but
> I THOUGHT it worked OK (currents lower than that).
>
> er.. maybe a leaking cap? a Tantalum or ceramic disk? A WRONG value
> R someplace? Swap any standard electrolytics for Tantalum.
>
> Are those the LF88 specs or the F88 specs? If I recall, the LF88 was
MUCH
> better. Can you try an LF88? I have an extra SOIC18 version..

Even though my problem turned out to be an apparent bug in the hardware,
I wanted to comment on this last part.  AIUI, all parts have the same
specs except that the L (low voltage) parts are guaranteed to work at a
lower voltage.  Voltage certainly plays an important role in how much
current is drawn, so the L parts are "better" in that respect, but they
aren't otherwise different from the 'non-L' parts.  IOW, at 5V they are
all the same.  ;-)  The DS1307 requires at least 4.5V, but I'm sure
there are some 2V or 3V minimum parts available.

I've been experimenting, now before I put it to sleep, I power off the
EEPROMs, DS1307, LM34 and my external Vref for the ADC.  Sleep current
for the whole circuit is <5uA.  The DS1307 runs off a lithium backup
cell when the circuit is asleep.  The square wave output of the DS1307
continues to function with no power applied to the Vcc pin (Vbat does
the job).  I use a way big (3.3M) pull-up on the square wave output for
super-low current draw (1.5uA) during the low half of the cycle.  The
RB0 int fires on the falling edge with no problems caused by the really
weak pull-up.  The duty cycle is only 1Hz so rise time is not an issue.
The 1.5uA is small but it still accounts for a large chunk of the total
sleep current of the circuit.

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