SN65DP149: SN65DP149: DDC operation

Anton Kanyshev

Part Number: SN65DP149

Greetings!

I'm using the SN65DP149 as DP++ to DVI retimer, but right now I'm stuck with DDC problem. GPU is trying to reach the display through I2C, but on display's side is silence - constant 5V. Not even a single bit. I'm attaching shematic.

What can cause such behavior?

over 6 years ago

0 Michael.Walker over 6 years ago

TI__Mastermind 19720 points

The SCL_SNK and SDA_SNK should have 2K Ohms pull up resistors to 5V not 3.3V like in the schematic on the datasheet in figure 28.

0 Anton Kanyshev over 6 years ago in reply to Michael.Walker

Prodigy 210 points

Already found it and fixed it, thanks. But this did not resolve the problem. So, what else?

0 Michael.Walker over 6 years ago in reply to Anton Kanyshev

TI__Mastermind 19720 points

The 10K resistors should be 65K resistors. That could be causing your issue.

0 Anton Kanyshev over 6 years ago in reply to Michael.Walker

Prodigy 210 points

And this did not change situation either. Any ideas?

0 Michael.Walker over 6 years ago in reply to Anton Kanyshev

TI__Mastermind 19720 points

Can you send me an updated schematic?

0 Anton Kanyshev over 6 years ago in reply to Michael.Walker

Prodigy 210 points

Sure! Right now schematic looks like this:

0 Michael.Walker over 6 years ago in reply to Anton Kanyshev

TI__Mastermind 19720 points

Why is your SDA_SRC and SCL_SRC labeled DP_CH2_AUX- and DP_CH2_AUX+? That is an I2C data not a differential data.

0 Anton Kanyshev over 6 years ago in reply to Michael.Walker

Prodigy 210 points

Because GPU has only AUX ports, therefore it's sending I2C-over-AUX.
Just like in this topic: e2e.ti.com/.../603019

0 Michael.Walker over 6 years ago in reply to Anton Kanyshev

TI__Mastermind 19720 points

you are using the incorrect part for this application if you want to have AUX+ and AUX- come into the device and be converted to DDC you need to us the SN65DP159RGZ 48 pin package. The DP159 can take in the AUX+ and AUX- and convert it to DDC.

0 Anton Kanyshev over 6 years ago in reply to Michael.Walker

Prodigy 210 points

Am I understanding you correctly? The SN65DP149 will not comprehend AUX on DDC pins, even if GPU sending clear I2C signal through it? So this connection is incorrect, despite your colleague specificaly told (source: e2e.ti.com/.../2219770 that this connection is doable?

0 Michael.Walker over 6 years ago in reply to Anton Kanyshev

TI__Mastermind 19720 points

are you using the GPUs AUX lines to send out signals in the I2C format, meaning that the AUX- will be the data of the signal while AUX+ will be the clock of the I2C signal? can you send me scope captures of the AUX+ and AUX-? The AUX- and AUX+ are usually compliments of each other which will need the DP159 to translate to the clock and data lanes of I2C.

Because of the holidays, TI E2E™ design support forum responses will be delayed from Dec. 25 through Jan. 2. Thank you for your patience.

Interface

Interface forum

SN65DP149: SN65DP149: DDC operation