QUAD DAC TLC7226C questionÉ

Discussion in 'The Projects Forum' started by rougie, Aug 28, 2012.

  1. rougie

    Thread Starter Active Member

    Dec 11, 2006
    410
    2
    Hello,

    I am trying to use the TLC7226C from TI and there is something weird happening here! I was wondering if anyone has already used this chip before.

    The TLC7226 is a 4 DAC in one package with 2 combinatory input pins to allow the DAC selection. It also has four voltage outputs (one per DAC). It has 1 common 8 bit bus (DB7-DB0) for binary input value to be converted to voltage. You may see its spec if you Google the part.

    I have 8 output pins from a uC connected to the 8 input pins of the TLC7226 which ramps up in binary value from 0 to 255. In correspondence
    to this binary value I can read the DC converted voltage on pin#1 labeled (OUTB in the spec). It goes from 0 volts to 5 volts which is the maximum voltage range I have provide to pin#4 (REF). Please view attach file for schematic.

    However here's the problem. When pin#1 is approximately at 4VDC, on my VOM I see a quick spike to 6.0 VDC and back to 4.01 VDC. Then it continues to ramp to 5VDC and then restarts from 0 volts again????

    Does anyone know why this would happen.... ??

    TESTS ALREADY CARRIED OUT:
    - Verified that all 8 bit bus lines from the uC to the TLC7226 part correspond correctly
    - Tried separating grounds between pins 3, 5,and 6.
    - Respected the values as per recommended operating /max conditions tables


    Thanks for all help!
    r
     
    Last edited: Aug 28, 2012
  2. crutschow

    Expert

    Mar 14, 2008
    13,056
    3,245
    How rapidly are you sequencing the bits? Can you slow it down?
     
  3. rougie

    Thread Starter Active Member

    Dec 11, 2006
    410
    2
    Bits are sequencing at about 5HZ... enough to follow the bit pattern!

    thanks for your reply
     
  4. rougie

    Thread Starter Active Member

    Dec 11, 2006
    410
    2
    Nevermind..........

    You all may try this.....

    Connect your VOM directly to a power source and start from 0 Volts and slowly move up to 5V. At approximately 4VDC, (as per my VOM... it might be slightly different on yours), the VOM changes scale... hence the quick peak to 6VDC.

    r
     
  5. crutschow

    Expert

    Mar 14, 2008
    13,056
    3,245
    Most multimeters are 3 1/2 digit and change scale at 2V. Some are 3 3/4 digit and change scale at 4V (as apparently yours is).
     
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