reading a 5v sensor with a 3.3v adc

[4mla1fn]

i need to add a 5v sensor (with max 5v output) to an existing 3.3v system. i could simply use a voltage divider with two resistors and put that into my 3.3v adc. i've also seen where the stepped-down voltage is first put into a non-inverting unity op-amp and the then into the adc. is one approach better than the other? thanks.

[jeffs555]

The main reason for using an op-amp is to lower the driving impedance into the adc without increasing the load on your sensor. The reason for lower impedance is to get better dynamic response. Your adc will have a spec for maximum input impedance. Using a resistive voltage divider, you will have to make sure the resistors in the divider are lower than this spec. The problem is that lower value resistors will increase the load on the sensor so you also need to check the drive specs for the sensor.

[4mla1fn]

awesome. it's all coming back to me now; been 20yrs since i first learned this stuff. i'll add the op-amp. thanks alot.