I’m designing battery powered application in the form of a sensor with an onboard high-precision (20 to 24 bit) sigma-delta ADC that measures a couple of load cells in a Wheatstone bridge. My question deals with how to properly power such a device to both meet the low-noise requirements of the ADC as well as long battery life for the overall product.
I intend to supply the sensor with two series connected single-cell alkaline batteries, for instance 2 x AA batteries providing a nominal voltage of 3V. Looking at the discharge curve of a typical alkaline AA battery I can see that the cell voltage ranges from 0.8V (discharged) to 1.5V (nominal). In other words, I will end up with a supply voltage of 2 x 0.8V = 1.6V when I have used the full capacity.
The ADC that I intend to use has an analog supply requirement of MIN 2.7V to MAX 3.6V. Therefore, to make full use of the battery capacity I will need to use some kind of power management circuitry that can boost my battery voltage (VBAT: 1.6V - 3V) to a stable 3V - 3.3V. To do this I have been looking at the possibility of using a DC/DC step-up regulator. The main problem I see with such a device is the large ripple it produces at the regulated output voltage which might be compromise the accuracy of the ADC.
So the dilemma I’m facing is that I would like to have as long battery life as possible and at the same time avoid compromising the accuracy of the ADC. I don’t have any previous experience in using switching type regulators. What type of power management would you recommend for my specific application? Is there a good practice?
- ADC Type: MAX11206 (20-bit single-channel delta-sigma)
- Current consumption: ADC consumes 300uA during operation and 0.4uA during sleep. The rest of the board draws 400uA in average.
- Voltage output: 3.3V used for AVDD, REF and VE for ADC/brige and microcontroller on the board.
- ADC-Bridge Connection: Ratiometric connection (where bridge excitation voltage is the same as the reference voltage).
- Sampling rate: Very low (1 sps)
Looking forward to hear your suggestions.