Hi,
Knowing the desired output voltage and current, what are some things to consider when selecting R1 and R2 when designing an adjustable output? For example, my customer wants a 3.3V output at 1A with an input of 5V.
Other than choosing "lower" values for resistance (perhaps <10kOhm per resistor) for less power dissipation, what are some other factors to consider when choosing R1 and R2?
Thanks,
Lauren
Hi Lauren,
R1 and R2 will affect the tolerance of Vout. The datasheet Vout accuracy specification does not include R1 and R2. The goal is to choose a good combination of R1 and R2 that will yield the desired Vout (or as close as possible). For best accuracy you will want to include the affects of the feedback pin current, which ideally is 0A but never will be. Here it is typically 10nA with a maximum worse case value of 100nA. By convention, positive feedback current flows out of the LDO so the output voltage will be:
Vref*(1+R1/R2) + Ifb*R2
Thanks,
Stephen
