SN75DP130: support DDC or AUX at same path

Polly

Please refer to Figure 23 or 24 of the SN75DP130 datasheet. You need to use external FET to short out the coupling capacitors on the AUX channel so it can be DC coupled for DDC.

Thanks
David

Dear David,

Thank you. But customer block diagram's connection is different than figure 23 and 24. They want to connect AUX_SRC and DDC together. Is it workable or any side effect at DP++ application? Thanks again.

Best Regards,
Polly Chung

Polly

DDC is a DC coupled interface while AUX is a AC coupled interface. You have to use FET switch to short out the coupling capacitors on AUX channel so it can be DC coupled for DDC usage.

Or if the customer does not want to use the FET switch, then they can follow the implementation in Figure 24.

Thanks
David

Dear David,

Thanks for your reply.

Our detail block diagram is as below picture. We use TI SN74CBT3306 to separate DDC/ AUX source, and choose one of them connected to SN75DP130.

Could you help to point out where we need to add FET or capacitors for DP++ application, Thank you.

Ian

If CPU has separate DDC and AUX bus, why do you want to combine them? You can connect CPU DDC to DP130 DDC bus and CPU AUX to DP130 AUX_SRC.

If you do need to combine them, then you need to have a MUX inside the COM module to switch between DDC and AUX, and then FET switch outside the COM module to isolate the coupling capacitor on AUX, or

Have a MUX inside the COM module, and then follow figure 24 to implement a solution without the external FET.

Thanks
David

Dear David,

Due to COM Express SPEC, we need to combine DDC/AUX and use same path connected to carrier board (SN75DP130 on carrier board).

Already update our application block diagram as below picture. Could you help to check if there is any problem for DP++ function, thanks!!

Ian

The block diagram is OK. I am not familiar with the NX3DV221 part, please make sure this part meets the electrical spec requirement of both DDC and AUX interface.

Thanks
David