DS90CF384A: DS90CF384A Design review

Dharun Sangrithiyayan

Part Number: DS90CF384A

Hi Team,

we have some queries regarding the DS90CF384A design.
1. What value of termination resistance should be used for R1:R29?Do we need to match the 50ohm impedance even if we place termination resistors?
2. Do the PWR DWN pin have any internal pull-up resistance?
3. What is the purpose of the RxOut23 RES pin?

Also kindly review our schematic design and please provide us with the complete datasheet/reference manual.

Regards,
Dharun Sangrithiyayan S

over 4 years ago

0 Michael.Walker over 4 years ago

TI__Mastermind 19720 points

Hi,

1. The LVDS inputs to the DS90CF384A should have a 100 Ohm terminating resistor between the RxIN+ and RxIN- lanes.

2. The PWR DWN should not have an internal pull up resistance.

3. Which pin are you specifically asking about? Can you point it out in the package diagram?

Yes, Can you attach the schematic? the datasheet is online here:https://www.ti.com/lit/ds/symlink/ds90cf384a.pdf?ts=1633626095127&ref_url=https%253A%252F%252Fwww.ti.com%252Fproduct%252FDS90CF384A

Regards,

Michael W.

0 Dharun Sangrithiyayan over 4 years ago in reply to Michael.Walker

Prodigy 40 points

Hi, Michael thanks for your reply.
1. Please find the attached image of the schematics for your reference.
2. The termination resistors I'm asking for are in the output(RXOUT).
3. I have attached the image indicating that pin.

Thanks&regards

Dharun S

+1 Michael.Walker over 4 years ago in reply to Dharun Sangrithiyayan

TI__Mastermind 19720 points

Hi Dharun,

1. Your Schematic looks correct.

2. You do not need termination resistors for RxOUT.

3. There are 28 Rxout pins because there is 8 red RxOUT, 8 blue Rxout, 8 green Rxout, 3 control Rxout (HSYNC, VSYNC, DE), and one unused Rxout. Which pins correspond to which signal depends on the LVDS input signal. Here is an example from the DS90CF384A 's datasheet and the 948's datasheet. RxOUT26 can be left as no connect.

Regards,

Michael W.

0 Dharun Sangrithiyayan over 4 years ago in reply to Michael.Walker

Prodigy 40 points

Hi Michael

Thanks for the reply.

1. Regarding the termination resistors, I'm referring to the 50Ohm impedance matching referred to in the EVK. Still, confused whether to place that termination resistor?

0 Dharun Sangrithiyayan over 4 years ago in reply to Dharun Sangrithiyayan

Prodigy 40 points

Hi Michael

We have another query regarding the design.

1. To avoid crisscrossing in routing can we swap the RXOUT signal within the same color signal(eg; Rxout0(R0)TO RXOUT6(R5))?

2. For pin mapping of RGB signals, whether we have to follow the datasheet or application note. We have done the pin mapping according to the below snapshot. Please ensure whether we are correct.

Thanks & Regards

Dharun S

+1 Casey McCrea over 4 years ago in reply to Dharun Sangrithiyayan

TI__Guru** 103215 points

Hello Dharun,

The 50 ohm resistors are optional. They are used for wave shaping the single ended outputs to minimize overshoot and undershoot seen at the input of the next receiving device. The size of these resistors can also be tuned based on your design to optimize the signal quality.

You can change any bit ordering as needed since the DS90CF384A acts as a simple deserializer. It does not know what signals it is passing - it just receives 28 bits per figure 10 in the datasheet and sends those out the corresponding pins on the parallel side. So if you swap two bits on the parallel side, you need to make sure to swap those data bits within the LVDS input stream side as well.

This depends on the format of the incoming data from the LVDS side. So consult the LVDS source formatting information to see which R/G/B bits correspond to which bit positions within the LVDS stream and then you can use the diagram in figure 10 for how to connect the outputs accordingly

Best Regards,

Casey

0 Dharun Sangrithiyayan over 4 years ago in reply to Casey McCrea

Prodigy 40 points

Hi Casey

Thanks for the answer. I still have one more question

1. Do we need to do the 50 Ohm trace Impedance matching if we place the termination resistors?

Thanks&Regards

Dharun

+1 Casey McCrea over 4 years ago in reply to Dharun Sangrithiyayan

TI__Guru** 103215 points

Hello Dharun,

Yes that would be recommended

Best Regards,

Casey

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DS90CF384A: DS90CF384A Design review