I have a customer that needs to digitize the output of a strain gauge. Their power source can vary from 1.6 to 3.6V and is capable of supplying no more than 200 uA. Ideally, they want to use a differential input A/D and want a SPI output. Sample rate is super low. Maybe one sample per minute. 8 bit accuracy is acceptable. The design is high volume 100-200K units and very cost sensitive The Maxim MAX1391 is being considered. As an alternative, I offered the AD7468 + AD8237. I have a few questions:
- Do we have a differential input, low cost A/D that can operate at 1.6V?
- The 7468 datasheet recommend using the ADR318 as a reference/power supply for the ADR318 as a 1.8V reference. This part is EOL. I don't see another 1.8V reference to choose from. Please offer suggestions of 1.6 or 1.8V references. The customer does not want to use a higher voltage reference.
- I assume that if the reference can source enough current, there would be no problem powering the AD8237 with it either. Do you agree?
- Can you propose any lower power or cheaper away to solve this problem?
Attached is my initial idea
A couple new thoughts. Perhaps the AD8236 is a better fit for the Instrumentation amp. It is much lower power. Regarding the reference, I looked for something cheaper than the Maxim part and considered the following:
- TI REF3318 - $1.03 on Digi-key
- Intersil ISL60002 - $1.12 on Digi-Key
Both are very low power