SNOS412O February 2000 – June 2020 LM1117
The LM1117 adjustable version develops a 1.25V reference voltage, VREF, between the output and the adjust terminal. As shown in Figure 10, this voltage is applied across resistor R1 to generate a constant current I1. The current IADJ from the adjust terminal could introduce error to the output. But since it is very small (60µA) compared with the I1 and very constant with line and load changes, the error can be ignored. The constant current I1 then flows through the output set resistor R2 and sets the output voltage to the desired level.
For fixed voltage devices, R1 and R2 are integrated inside the devices.