Dear Sir/Madam,
We are using PGA900 to make pressure and temperature sensor. We use PGA900 in 4~20mA mode, which means we drive DAC to output current within 4~20mA for pressure or temperature. Our design is based on the 4~20mA reference design in PGA900 datasheet.
Basically it works fine. The static current of PGA900 is less than 3.5mA. So it is no problem to generate 4~20mA current by DAC. But recently we met a problem. Sometimes, especially when the ambient temperature of PGA900 is higher than 80C, the static current of some PGA900 increases and is even higher than 4mA, e.g., 5~6mA but not a fixed value. The ADC/MCU/DAC parts of PGA900 still works fine. That means the value of pressure/temperature has to be higher than the increased static current of PGA900. Otherwise the static current will cover the real current generated by DAC. Sometimes the issue happened when the sensor has worked for several weeks.
We did temperature cycle testing for this circuit, the static current was quite stable with temperature changing if this issue didn't happen. Sometimes when we resoldered PGA900, the issue was disappeared. So we don't know which factors could cause static current of PGA900 increasing a lot with temperature changing. If it is a soldering issue, we don't know which pins could cause such kind of issue.
Could you please help us on it?
Thanks.
Jin
