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Part Number: TIPD193
I implemented the TIPD193 reference design two times on one PCB. I use a local 5V power device LP2951ACM.
The problem is, that the channels often apply 5V at the output of the INA326 at startup, even the sensor value would be different.
I adapted it for thermistors, so the resistance range is different --> sensor 10k.
R1 = 392k
R2 = 330k
C2 = 482pF
R3 = 270
Sometimes a power toggle helps to bring the device back to normal work or also deconnect the sensor and reconnect it.
Zak Kaye Precision Amplifiers Applications
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In reply to Zak Kaye:
I use the REF200U for biasing.
I do have terminal blocks for the connection, that works good.
In reply to Peter Huber:
Thank you for your update.
We do use the PCB for different configurations of PT100 and Thermistors at different temperature ranges (normally around 0...50 or -20...100 degree Celsius).
The schematic contains the values for a PT100 setup with a high gain / the thermistors setup has a gain of -1.79, so rather small.
I do have X7R capacitors on the PCB. The PCB is fully produced from a PCB manufacturer and we solder only the 4 parts to adopt the sensor/temperature range as listed in the first post (use of a SMD tweecer solderer). Do you think the flux contamination can also be a problem on that small area?
You mention saturation on the rails. Does it not recover from saturation if the sensor signal is stable?
Is it maybe needed to delay the current reference startup? (I do not measure the problem as long as no sensor is connected)
We do have an older device with 12 channels on one PCB and I was told, that the error also occured there - they just made some power cycles.
I took two devices from an other project, each device has 3 boards (6 channels) in use to test for the PT100/Thermistor - the devices are also quite new, so we do not have much experience.
I did find another board which hat that suspicious error.
Up to now all boards with the error do have a Thermistor connected. The Thermistors are connected as a PT100 in 3 wire connection (two wires are wired to one pin of the Thermistor and one wire to the other pin). We do have cable length within 1...5m.
The error occurs at power up - I would not think about it much if it is only when I measure on it :-(
--> then that channel is stuck at 5V!
As I said sometimes a power cycle helps - sometimes not. What always helped me was to detach the sensor GND connection.
On the other side, all boards which do not show the error, do not go into error when I measure at the R1.
I also tried to clean the PCB, first it looked a bit better. But then I moved the setup to a different working space and now it is back that it has the error sometimes. I do not have some kind of a special PCB cleaning solvent. I ordered one and will test with them tomorrow.
Thank you very much for your suggestions.
As I have written above, the R2 has also a wrong value - above the power supply level. Thats the point where I'm curious about. I'm not sure if something happens during the startup.
The value is stuck and it seems to be stable. I let it run the whole day avter recovering from the error and the value was stable (only some shift due to temperature increase - the value at the output fall about 0.2V).
I'm not sure if it is good to exchange parts - because you are also still think about the leakage currents. May I remove the R1/R2/C2 (which we soldered by hand) - the rest of the board was manufactured as serie.
Yes when I disconnect ane reconnect the GND of the sensor as long as the board is still powered brings the output back to normal value.
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