I am looking to use an LDO with a negative adjustable output voltage. I have found two products sold by TI that have similar schemes for setting the output through external resistors.
I am slightly confused though, as one of the resistors in each scheme is illustrated as a potentiometer. Why is this so? Can a fixed value resistor be selected instead?
Also, the first regulator series (LM79XXAC) have fixed negative outputs but external circuitry can be configured to make it adjustable. For instance, take the -5-V fixed LDO in adjustable output configuration.
If this was instead the -12 V fixed output version, would the output equation change such that 12 V is substituted for 5 V in the above?
Finally, both datasheets do not seem to provide an input voltage range. Is there something I am missing? I need to figure out how to select a value of Vin for a given Vout.
Here are links to the Datasheets: