Other Parts Discussed in Thread: TLV4170
I am troubleshooting an issue on a design that uses an ADC0808-N. One observation I have made is that I get different behavior depending on whether I apply voltage to the VCC pin before VREF, or vice versa.
SETUP:
The VCC pin is receiving power from a +5 V supply and is connected directly to the power rail.
The VREF+ pin is connected to +5 V derived from a separate power supply than the VCC +5 V rail. The derived +5 V goes through an op-amp voltage follower (TLV4170) who's output is then connected to VREF+.
The VREF- pin is connected to ground.
TEST:
When I am powering up the ADC, if I apply voltage to VCC first, and then to VREF+, the ADC works as expected.
However, if I apply voltage to VREF+ first, and then to VCC, I notice that the VREF+ plus pin has dropped from +5 V to about +4.6 V. The output of the voltage follower has dropped to +4.6 V even though its input is still at +5.0 V. It seems like the ADC is in some state where the VREF+ pin is loading down the op-amp.
Anyone know anything about this behavior? Any ideas would be appreciated!
