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HDMI DDC Failing Capacitance Limit

Question asked by cdsteinkuehler on Jan 11, 2011
Latest reply on Feb 25, 2011 by mattp

We sent a unit using the AD9889BBCPZ-80 HDMI transmitter for HDMI compliance testing, and among the various problems causing us to fail (mostly minor video formatting glitches), the report indicated the measured capacitance on the DDC lines was too high (73 and 78 pf, with anything over 50 being a failure).


We are running the AD9889 along with the ESD protection chip as implemented on the reference schematic (NXP IP4776CZ38).  The traces on the board go directly from the connector through the ESD chip, and then to the AD9889.  I did not remove the plane layers from under the DDC traces, but I can't imagine this would cause that much stray capacitance!


Any suggestions as to why the measured capacitance is so high?


The test was performed with the power on, but there is an option to do the test with the power off.  What is the recommended option when testing the AD9889?