I need to know if the TX outputs of the ADV7626 are fully HDMI compliant when acting as an HDMI source device.
Yes, this device is an HDMI product and we have passed HDMI compliance tests with this device. Is there some specific thing you are concerned about?
My only specific concern is how much current will flow back into the TMDS output lines if the ADV7626 is powered down when connected to a sink device. If too much current flows there is the danger of 'back powering' the source by the sink.
A similar situation can arise on the TMDS inputs being 'back powered' by the source.
If the ADV7626 is HDMI compliant this should not be a problem.
Do you have one of our evaluation boards which has ADV7625?
Yes I do have the evaluation board and have taken a look at the schematic but I haven’t yet tried to measure and possible ‘back powering’ currents into the TMDS ports.
Will Haylock (Senior)
Senior Electronics Engineer
p: +44 (0) 333 2079766
Regarding the output side (TX TMDS): These pins have a standard ESD structures on them. Normally these TMDS lines are connected to the sink which will have 50 Ohm pull up resistors to 3.3V. In the case where the ADV7625 is not powered and the sink is powered with the terminators turned on the current flow will be:
Sink 3.3V -> through termination resistors -> through cable -> through TX ESD structure -> ADV7625 power rail.
Absolute worst case current would be ~(3.3 - 0.7) / 50 Ohms = 52mA
We have run these parts in this configuration many times without damaging them. Which specific CTS test are you referring to? I cannot seem to find it (or missed it while looking at spec) . Also note that normal sinks will not enable the termination resistors until it sees a connected source. A powered down ADV7625 will look like no source is available.
Regarding the input side (RX TMDS): These pins also have the normal ESD structures on them. The RX receivers are high impedance and the source only uses current sources to pull the TMDS line to ground. Therefore there is no way for current to flow from the source over the cable to the ADV7625 power rails.
If you are worried about 'sneak paths' you also need to examine the DDC lines.
The ADV7625 TX side is not a problem because the TX side supplies the DDC_5V which drives everything down stream.
For the ADV7625 RX side, the DDC_5V will flow through the ESD structure of the DDC_5V pin on the ADV7625 (note this pin is a high impedance input). Again we have note seen any issues when testing with this parts here
Of course I'd need to review the board schematic with specific intent to examine 'sneak', 'zombie' or 'back flow' paths and see how they effect the system in general. Keep in mind also that our TX and RX TMDS also have ESD protection components on them in our reference design. These will effect the back flow current pathing.
CTS Version 1.4b.
The test I am concerned about is Test ID 7-3: TMDS – Voff.
Assuming that I have read the CTS correctly - this test sets a leakage current limit of effectively 50Ohms/10mV = 200uA on each TMDS line. We have fallen foul of this compliance test on a earlier product.
CTS 7-3 is a leakage test. I don't have the equipment here to duplicate the test. All I can really say is that the part passed the test when we released the chip.
Thanks for your reply.
The amount of current that flows back through the ESD protection devices to ADV7626 supply rail will also depend upon what the impedance of the ‘off’ power supply rail is.
I will measure the current on the unpowered dev board.
P.S. there is no indication on the ADV7626 datasheet that the device is HDMI compliant, whereas, for example, the AD8192 has the explicit statement that the device is ‘Fully HDMI 1.3a transmit and receive compliant’.
Please can you point me to the location of the latest version of AVES3 so that I can fully evaluate the ADV7626 on my ADV7625 eval board.
I am using Windows 10 Pro.
ADV7625 docs can be found here
Advantiv™ EVAL-ADV7625-SMZ Video Evaluation Board
Aves3 can be found here
Advantiv™ Video Evaluation Software 3 (AVES3)
AvesBlue can be found here
Advantiv™ Video Evaluation Software (AVESBlue)
I have not done any real testing on Windows 10 however I have not heard any problems regarding Win10 and AVES.
Thanks for the software link, however there is now a problem with the Advantiv USB device driver.
It installs ok - but when the eval board is connected to the PC USB port device manager reports “Unkown USB device (Device descriptor request fail).
If you are using the EVAL-ADV7625-SMZ, we suggest that customers use the (dynamic) software driver to configure the ADV7625, rather than the (non-dynamic) scripts/AVES3.
Also, whether you are using the software driver or scripts/AVES3 to configure the ADV7625, you should use the
ADSP-BF524 RS232 port (P1) for communications, not the ADSP-BF524 USB port. The ADSP-BF524 USB port serves a different purpose (BLIMP/OSD data input).
Yes I am using the EVAL-7625-SMZ.
Sorry, I have no idea what this dynamic software driver is or where to find it or what to do with it?
I assumed that I could control the settings of the ADV7625 on the EVAL board by installing AVES on my computer and connecting to the USB port on the EVAL board.
The application binaries mentioned here:
are the same thing as the software driver. They run on the ADSP-BF524 at power up and configure the ADV7625 to receive and transmit data.
There is more information in the user guide, also found at the link above.
I have found a computer with an ‘old fashioned’ serial port and Windows XP - AVES3 now appears to work correctly with this set up – this will suffice for me to climb the learning curve!
Do you have a schematic of the TMDS outputs and ESD protection for the ADV7626? Is it the same as the AD8192 that we current use?
In the link I posted above:
you can find the schematic for the EVAL-ADV7625-SMZ board. We have an ADV7625 on this board and customers use it to evaluate ADV7625/ADV7626/ADV7627 by programming the appropriate software driver application binary.
I was referring to the internal schematic of the TMDS output stage of the chip not the EVAL board schematic.
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