What to look for in an external ADC

Discussion in 'Embedded Systems and Microcontrollers' started by osx-addict, Aug 8, 2012.

  1. osx-addict

    Thread Starter Member

    Feb 9, 2012
    I've got a hypothetical question for you all.. IF I were to go with an MCU that did not have an ADC on it and you wanted to included an external ADC connected via SPI or I2C (for example), what would you look for spec-wise on such a part -- specifically sample times, # of channels, resolution,etc..

    Most of the ADCs I see in μC's are either 10 or 12 bits of resolution and have pretty fast sample times (~1Msps for example on some PICs).. One other parameter on this would be part cost -- I'm not interested in the $10/ea in small qty parts... I could however go with say 4 single channel ADC's since I don't think it would be an issue design wise -- if that route would be cheaper than a single 4-channel ADC for example.. Is there anything else I need to look for? Obviously single-ended inputs to allow reading from thermistors and whatnot..

  2. JohnInTX


    Jun 26, 2012
    When you use an on-board ADC, you fit the app to the ADC and that's frequently good enough.

    Going off board opens up a huge number of options that just don't have any pat answers. If all you are doing is compensating for the lack of an ADC on-chip, you pretty much can get away with anything that has the specified number of bits, channels etc. Implement it like the datasheet says and rock on.

    If you are looking for something better, you'll have to specify your application including ADC type, number of bits, accuracy, monotonicity, conversion speed, channels, input multiplexing etc etc etc. Each ADC type has its advantages and implementation requirements and quirks. There are times when you want to use SAR, delta-sigma, integrating, flash etc but only you can make that call. Even within each type there are optimizations and trade-offs.

    Check out some manufacturers' knowledge bases like this to get a feel for what's out there and decide what specifics will work for you.
  3. osx-addict

    Thread Starter Member

    Feb 9, 2012
    Thanks, as usual, John! I'll probably stick with my previously picked PIC32 part and just move forward with my design but wanted to check.. I got pricing on a IAR compiler for the other part I was pondering but almost croaked at the price.. Yikes! :eek:
  4. t06afre

    AAC Fanatic!

    May 11, 2009
    What sort of ADC will depend on your application needs. If I remember correct you are quite new to this kind of stuff. So I would settle for a 14 or 16 bit ADC. It is no help in having a lot of bits. Then all sorts of noise eat up this advance.
    osx-addict likes this.