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ADV7280 - digital outputs

Category: Hardware
Product Number: -
Software Version: -

Hello,

I am using EVAL-ADV7280. When I check the LLC pin with oscillescope, I always see the -1V to 4.6V 27MHz clock signal.

Also when I ckeck the P0 to P7 Video Pixel Output Ports, I always see same voltage levels -1V to 4.6V.

When I check datasheet is says:

DIGITAL OUTPUTS
Output High Voltage:
2.4V   for   ADV7280 only

Output Low Voltage:
0.4V   for   ADV7280 only

Why am I see this ~6Vpp signal ? Why it is not 1.8V ?

  • Hi,

      Depend upon the loading, the voltage range will get vary but it should not exceed the range that specified in the specification.

    DVDDIO supply of the ADV7280 (TTL part) can be set to 1.8V and kindly note that in this mode the drive strength of all digital outputs must be set to maximum.

    Thanks,

    Poornima

  • There are multiple possibilities that can cause what appear to be over voltage (both positive and negative) in digital traces.

    1) Scope bandwidth too low,  for 27MHz you need at least a 100Mhz scope.  Higher is better.  For good scope viewing the scope needs to have a bandwidth greater then the 5th harmonic.

    2) Scope probes not calibrated.

    3) Bad ground connection between the scope and the eval. board.

    4) Poor layout or impedance mismatching on traces.  Can cause ringing which cause over shoots.  Ringing is caused by edge transition rates.  This eval. board should not have this problem.

    Regarding the data sheet a signal  is consider high when > 2.4V and low when < 0.4V