ADC+gain combo IC, anyone know ???

Discussion in 'General Electronics Chat' started by howdoesthatworkguy, Jul 25, 2007.

  1. howdoesthatworkguy

    Thread Starter Active Member

    Jul 23, 2007
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    I am setting up an h-bridge that will be driven by a 16F series pic. I need a current feedback look, looking at examples I need to use a gain amp if I use the typical current sense resistor setup on the lower part of the H-Bridge. Since the ADC is 10bit on the PIC and I am wanting something a little higher, does anyone know of a few good ADC/gain IC's with 12 to 16bit ADC and built in gain ?

    The H-bridge drives a 12v motor brushed, about 1amp draw. Something small in SMD and simple is what I am after
     
  2. Papabravo

    Expert

    Feb 24, 2006
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    In my experience it is not usual for an ADC to have a gain block. You might want to rethink the 12-bit / 16-bit part especially in a motor application. Are you at all familiar with low noise precision circuit design or are you just guessing on your requirements.

    Quick how many microvolts is 5/4096 ?
    And 5/65536 ?
     
  3. Distort10n

    Active Member

    Dec 25, 2006
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    Most of these that I have seen are in audio type of converters where an adjustable gain is used for the MIC preamp.
     
  4. Papabravo

    Expert

    Feb 24, 2006
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    Is there an external connection from the amplifier output to the ADC input?
    You wouldn't happen to have a part number or a link - would you?
     
  5. nanovate

    Distinguished Member

    May 7, 2007
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    Look at Analog Devices Current Sense Amplifiers section for an IC that you might be intereseted in.

    TI's Burr Brown group has many fine ADCs that have PGAs built-in but they are mostly the sigma-delta high resolution type. They also have the MSC121x 8051 + 24bit ADC. It is programmable via the serial port so you do not need to buy a seperate programmer.

    John
     
  6. howdoesthatworkguy

    Thread Starter Active Member

    Jul 23, 2007
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    OK, I am re-thinking this part. Have been looking at a lot of info on the web. It seems High Side Current Sense devices on a H-bridge are the way to go. Using the ADC on the PIC with 10bit res, I need a all in one device that can interface between the H-Bridge and the ADC. Would something like an LTC6101 work? the app note says high side sense is better than low side and that this device can read both the left and right side of the H-bridge. Can I just feed the - and + into 2 10 Bit ADCs on the PIC or am I missing something here. I tell you guys, I thought the digital part was hard, but this analog stuff really makes my head spin.
     
  7. howdoesthatworkguy

    Thread Starter Active Member

    Jul 23, 2007
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    PS, I forgot to ask if I am right in thinking that this device or simalar can be feed directly into an ADC on a PIC. It says differential output - +. Does this mean I can just feed the two outputs from the LTC6101 or (What ever you guys suggest) into two ADC's, or does the differentail output need to go into something else to give one input into a single ADC. The last time I delt with differentials was 15 years ago on my V8 making sure the 10bolt Chev diff did not explode when doing burn outs in my car.
     
  8. nanovate

    Distinguished Member

    May 7, 2007
    665
    1
    The LTC6101 is single-ended output on the OUT pin. You would connect that through a filter to the AIN of the PIC.

    Make sure the gain is set using a high precision resistor and that at full current you do not exceed the max input voltage to the PIC.

    To measure both legs of the H-bridge using two of them is easiest.

    John
     
  9. howdoesthatworkguy

    Thread Starter Active Member

    Jul 23, 2007
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    0
    Still stuck on the current sense, I have decided not to use an extra ADC and just use the internal ADC of the PIC, 10bit. But have not figured out how to create the feedback. High or low current sense, most say High, but is there a way of doing it with a few resistors (using some type of devider network) without any complicated IC's ?
     
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