AD8195 power consumption

Forwarding to the AD8195 expert

Guenter,

     Any progress? We are waiting AD response to release or not.

Thanks,

Steph.

No answer yet, trying to get in touch with them again right now.

Is pre-emphasis enabled, PE_EN = 1? If yes, the total current can approach the values you are observing, especially when the AD8195 TMDS output is floating.  Is the AD8195 output connected to a Rx device?

Is pre-emphasis enabled, PE_EN = 1?

As mentioned in my first post, we don't use preemphasis.  The measured voltage on this pin in 0V (PIN 29).

Is the AD8195 output connected to a Rx device? 

AD8195 is connected to a FPGA.  The connection seems OK since we can see video on the output of our project.

Note:

Project data flow

HDMI Connector    ->     AD8195     ->     FPGA     ->     HDMI TX IC     ->     HDMI Connector

One possibility is there could be dc current flowing between the AD8195 Outputs and the FPGA SerDes Inputs.  What is the FPGA input termination voltage and common mode voltage range?  Is this connection ac or dc-coupled?  Sorry if this information is in a separate thread. 

If dc-coupled and FPGA input termination voltage (VDDIO in figure below) is less than AD8195 VTTO (3.3V), there will be dc-current flow between the devices, limited only by the termination resistance.  Series ac-coupling would be recommended in this scenario. 

Hi Dave,

We are in ac coupled configuration.  After your last message we tought we could have a polarization problem since there is no DC path from sink terminaison to AD8195.  We added 200 ohms pull-ups and it worked.  Now the current draw to suplly AD8195 and the new pull-up is 168 mA ( about 18 mA for the pull-ups)  which is a lot better thant 290 mA.  However,  could it be possible to have an explaination about that?  Why does it work now?

Thanks

Note: 200 Ohms value was selected so that it doesnt' change the sink termination to much.  (50//200 = 40).   The traces between AD8195 and the FPGA are around 1 cm.

Charles

Hi Charles,

You result is unexpected, and will require some more digging to find out the root cause.  I'll see if I can reproduce your issue in our lab.  In the meantime, you might consider a larger value resistor than 200ohm, perhaps 1-2kohm to further reduce the change in the impedance discontinuity.

Dave

Any progress?

Thanks.

I have tried unsuccessfully to replicate this issue in our lab.

I have tried several AD8195 evaluation boards.  Here is my setup.

Video Source -> Short Cable -> AD8195-EVB -> Short Cable -> Ac-coupled digital crosspoint to mimic ac-coupled FPGA as in your application -> Monitor

Here is the AD8195 currents I observe:

TX_EN = 0, PE_EN = 0: 17mA

TX_EN = 1, PE_EN = 0: 162mA

TX_EN = 1, PE_EN = 1: 282mA

The results are consistent board-to-board as well as repeatable after numerous power cycles.

Could you check the current you observe with TX_EN = 0 as well as PE_EN = TX_EN = 1?