Other Parts Discussed in Thread: TMP392, TMP390,
Hello,
I am having the same issue as was asked about in this earlier thread:
The OP was having trouble getting the TMP709 to switch for a 30 degree C setting.
In one of the answers, Ren Ren Schackmann points out:
"...TMP709 is not specified for temperature accuracy in the range you're using it. It is specified for 60 to 100C..."
And the OP switched to a TMP392 to solve the issue.
I'm confused, as the spec sheet clearly indicates, on page 8, that the TMP709 supports from 0 C to 125 C: "The TMP709 temperature threshold is programmable from 0°C to 125°C"
Page 6 of the spec sheet shows graphs from 0 to 120 for Rset values and Temperature errors.
Page 1 states the 60 to 100C mentioned by Ren, but from what I understand, that's for the +/- 3C accuracy.
What am I missing? I thought I had read the spec sheet correctly for my specific application.
I'm trying to keep a hummingbird feeder from freezing, so my target set point is about 10 or 15 C. I'm testing at 25 C and my workbench is around 18C, so the heat gun should make it step past the trip point. My circuit is pretty much exactly as the example on page 1 in the spec sheet (hyst to gnd, = 2 C), except instead of the 60 C Rset, I'm using Rset that aims at 25 C (I think it's about 80k). And I'm simply testing the value at OT with a DMM (no microprocessor). I switched the 470k resistor with 10k as is recommended later in the spec sheet, and I'm missing the 0.1 uF capacitor.
This is the spec sheet I'm looking at: https://www.ti.com/lit/ds/symlink/tmp709.pdf
Given that TI recommends using the "newer version [of TMP709] available" TMP390, and that this worked for the OP, I do plan to try those next, but I'm hoping someone can shed some light on where or whether I'm reading the specs wrong, or if the specs themselves are wrong or incomplete?
Thanks,
-Nico