Why use a different circuit to create a positive voltage with the ICL7660, rather than running it “upside-down”?

Question

The primary use of the ICL7660 (and it’s many clones/alternatives) is to create a “negative voltage” equal to its input voltage, which it does with minimal external components.

However, in my application I’d like to create a voltage above a power rail for switching a high-side N-Channel MOSFET. The data sheet contains the following circuit:

This circuit isn’t as nice as the negative converter- it requires two additional diodes, which also introduces an additional double diode voltage drop into the circuit.

I was wondering why you couldn’t instead “flip” the first circuit around- after all, voltage is relative- by swapping the V+ and GND connections. However, I figured if such a superior setup was indeed possible, it would’ve been mentioned on the data sheet, or at least somewhere online. So- what’s the catch? Is it possible to run the ICL7660 upside-down, and if not, why?

Answer 1

The datasheet does give some clues.

From the datasheet.

It is most unlikely that any of the internal function blocks will operate on reverse voltages.

Answer 2

I was wondering why you couldn’t instead “flip” the first circuit around- after all, voltage is relative- by swapping the V+ and GND connections.

Most ICs will get destroyed if you power them from supplies with wrong polarity. There are a few specialized devices where this may not be a problem, but otherwise it's almost guaranteed destruction.

Depending on the process used, the dielectric isolation tubs, MOS body diodes, lateral transistors and the SCRs they form, or some other structure inherent in the IC process will start conducting with gusto. If the external reverse current is not well limited, large currents will flow and destroy the device.

This applies to pretty much any IC - ICL7660 is not special in that regard.

This circuit isn’t as nice as the negative converter- it requires two additional diodes, which also introduces an additional double diode voltage drop into the circuit.

You can always add external discrete small-signal mosfets set up as ideal diodes :) Although at that point a 555 oscillator has plenty more drive current and will do just fine as a crude boost driver. For such applications, feedback is usually unnecessary, since the load is well known, and the voltage stability is not a concern as long as some minimum voltage is maintained. 5- or 6-pin miniature package boost converters are plentiful and cheap, so if you want decent efficiency, they may be the best bet.