Bias V devider needed with with MAX1044?

[Phorhas]

Assuming that I use a MAX1044 charge pump and use it as a voltage doubler, any reason why I shouldn't take my referance voltage directly from the battery, as it is essentially 1/2 of V+ (if  V+  to the components is taken from the MAX1044) ?

[Primus]

The MAX1044 is awesome, but it doesn't give 18 V exactly (more like 17 V). If you use very efficient schottky diodes you will get close. In my circuit I am getting 17.7 V from a 8.92 V supply with schottkys. Your ideal reference voltage would be 8.85 V. That means you'd be off by .07 V. I don't know if that matters. If the 10% doesn't matter rule is in effect, you could probably go with it.

Some of the hardcore engineers on the forum might have another opinion, so don't take my word for it. I do recommend the schottky's, though. I also recommend that you use the BOOST pin on the 1044. It pushes the switching frequency well above the audio range.

[Phorhas]

True, that one... I guess I shouldn't be so lazy

[D Wagner]

If you want 18 volts, use the MAX1044 to generate -9v. 

http://www.geofex.com/circuits/+9_to_-9.htm

You won't have to mess with a voltage divider, as your ground is actully ground.

[Paul Perry (Frostwave)]

Thatvolt or so assymetry in the two halves of the power supply hasn't worried me, in any circuits I've used a doubler or inverter circuit with.
Where things DO get messy is when you want a stable regulated bipolar supply.
Sometimes I find myself using a low-dropout 5v reg to get a stable +5 from a 9v battery, (good down to a bit over 6V) then inverting the output to get 5V.
Now that ends up with +5 and -4something, but it's stable.... and on the 'bright' side, a lot of the new addio chips are pretty low max voltage anyhow!