I've added a test inverting charge pump to an LMR64010 based boost regulator. This regulator outputs +12V (exact value is 11.88V) from a 7.4V battery pack.
This is a notated image from a Maxim application note showing what I did. The output capacitors are whatever I had handy - 22u and 10u in parallel:
With no attached loads I get a value for -V of -11.65V. The immediate issue I noted was with an attached negative load of 1K for approximately 12mA, the voltage immediately drops off to -6.5V.
Varying the load on the positive side (with a fixed negative load) I get:
Neg Load Pos Load Neg output (V) -------------------------------------- 1k inf -6.50 1k 3.3K -9.95 1k 1.0K -10.30 1k 500R -10.38 1k 250R -10.40
So a rapid convergence to about -10.30 volts at a load that matched the negative load. Then little or no rate of return below that.
Is this a correct statement then: "an inverting charge pump must have a matching load on the boost converter output".
Is this how I should design the completed circuit (which is providing negative biasing for an opamp - not my design) ? So I'd put a 1K resistor across the +12V rail and then specify that loading (12mA or so) as a max loading for the negative rail?