Interface a 5v pressure sensor with a 3.3v ADC

Question

I'm trying to interface a pressure sensor (MPXV6115vc6u) with a 3.3v ADC. My board is providing a 3.3v (it's a XBee power regulated board, via a Li-Po battery).

To wire the MPX sensor, I need to:

1. Step-up the 3.3v to 5v to power up the sensor
2. Convert the 0-5v analog signal to a 0-3.3v to read the pressure value.

What's the best approach, considering that pressure sensor are noise-sensitive and that my board is low-power?

For 1, I can probably use a circuit like this.

For 2, what should I do to keep the full range? What's the best way to minimize the number of components (~combine 1 and 2).

Thanks!

Answer 1

Since your pressure sensor only uses about 6mA according to the datasheet you might be better off with a switched capacitor step up supply like this one: http://www.ti.com/lit/ds/symlink/lm2750.pdf

To get your analog signal down to levels you can read you could just do a simple voltage divider. Or you could use an opamp this paper probably gives you more information than you'd care to know but there's a good circuit at the bottom of it: http://www.ti.com/lit/an/slyt173/slyt173.pdf

Hope that helps.

Answer 2

You don't say if this is a one off design or a production design. If this is one off, I'd try to run it at the lower voltage. It may not work, as the on chip bias generators may struggle or the range could be suppressed, but it would be worth trying to run it at 3V (lower) and if it's stable over temperature you should be OK for 3.3V. NOT recommended for production, but maybe worth a try.

Answer 3

I do not agree with your version, it is better to supply the 5V sensor separately. But if you want to stick to your version, you could use a Logic Level Converter - Bi-Directional.Sparkfun.