I've got a small board with 2 TMP512's that I'm trying to use for remote temperature sensing using discrete transistors. I am not using the power supply monitor functionality of the TMP512 at all. In my design both Vin+ and Vin- are tied to ground and I've disabled the shunt measurement ADC in the Shunt Measurement Configuration Register (0x00). I can read the local temperature result register and it seems to be working great, however when I attempt to read the remote result 1 or 2 registers, bit 0 indicating the Diode Open Flag is always set (I have the remote channels configured for continuous conversion). I'm not sure what I'm doing wrong.
Here are some more details about my design:
- My remote sensing transistors are standard 2N3906 BJT's that are diode connected as shown in figure 21 b of the datasheet.
- I'm using 560pF filter capacitors for both remote channels, although the sensors are not being placed near any other electrical devices so noise should not be an issue.
- I'm using subregulator "Configuration 3" as shown in figure 22 of the datasheet, my V+ is 5V.
- After reading the Sensor Fault section of the datasheet I checked the voltage at DXP1 and DXP2 and both fluctuate between 1.23V and 1.29V. This is clearly less than (V+) - 0.6V = 5V - 0.6V = 4.4V in my case.
- All of my 2N3906's are brand new, but I've tried 6 of them just to be sure.
- I've tried reseting and then reconfiguring the TMP512 multiple times.
I'm really scratching my head on this one, does anyone have any suggestions?
