LSF0102: LSF0102 - How to analysis the pull high resistor (typ is 200k) for bias circuit

Hi Jason,

We highly recommend using a 200k resistor. From experiments in the lab, I can confirm that significantly changing the bias resistance will also significantly change the threshold and thus the operation of the device.

For a simple answer, a larger resistor will not turn on the bias FET enough for proper operation in some cases, and a smaller resistor will turn it on too much. Either case will result in an error in the operating threshold voltage, which can cause the output to be either too high or too low.

There's definitely some 'wiggle room' on the resistor value, considering that the device operates from 1V up to 5V and can translate any values in-between with at least a 0.8V drop. Doing some quick calculations, I see a range of 16uA to ~1uA through the bias FET depending on the operating voltages. I think the biggest danger would be providing too little current, which could cause the threshold to decrease.

Have you watched our video on the bias circuit? It might clarify some.