low negative voltage PSU for precision ADC

Jimmy,

powering op-amps (or ADCs) with dual supplies is a common requirement. There are multiple ways of solving this problem depending on what voltages are already available to you.

For example, if you have a positive voltage and need to generate a negative one a Cuk topology (like the one you found with the ADP1621) is an option. The same can be implemented with a ADP1613 requiring less components, although a cuk topology typically needs more components it is the least noisy option unless you want to follow it with a negative LDO.

Another handy topology is the inverting buck boost. This can be implemented with a buck regulator such as the ADP2300 (or many other more integrated parts). Here is AN-1083 describing how to do it.

Powering op-amps often leads to the need of a positive and a negative rail that are equal in voltage but of reversed polarity. In this case a coupled Sepic-Cuk could be handy, especially because the op-amp current requirements are balanced between the positive and negative rail.

This topology is covered as part of the ADIsimPower tool set by downloading one of the SEPIC_Cuk tool.

Here is the link for the ADP1613 tool.

http://download.analog.com/PMP/ADP161x_SEPIC_Cuk_Designer.zip

Another option is to start with an inverting charge pump such as the ADM8860 or ADP3506 followed by either a negative LDO or a LC filter.

In power the options are many and often are dictated by what's already available on the board or what else you are trying to power.

AnalogXPRT