DS90CF384A: DS90CF384A working

Sandeep Shinde

Prodigy 140 points

Part Number: DS90CF384A

DS90CF384A is used for LVDS to RGB conversion. But it does not work. What are the test points?

over 6 years ago

0 Ikechukwu Anyiam over 6 years ago

TI__Mastermind 35130 points

Hi Sandeep,

Can you be more specific about the failure? Are you getting no image on your display, or is there an image but it is incorrect/distorted? What resolution/clock frequency is this application? Have you checked the input/output signals (clock, data, etc.) for irregularities? Have you tried multiple units?

Regards,
I.K.

0 Sandeep Shinde over 6 years ago in reply to Ikechukwu Anyiam

Prodigy 140 points

There is no image on display. Input signals tested and they are proper. But ground plane (for LVDS GND, PLL GND and GND) is common. I think these ground plane should be separate.

0 Darryl Jeong over 6 years ago in reply to Sandeep Shinde

TI__Expert 4210 points

The grounds should be common.
Is the DS90CF384A integrated in the panel? or are you hard wiring?
When you state "proper" all we know is that it is toggling. This tell you nothing about the mapping.
You need to double check the mapping of the signal from the input of the serializer (not stated) to the mapping of the output of the deserializer.
This is what I think is the problem is.

0 Sandeep Shinde over 6 years ago in reply to Darryl Jeong

Prodigy 140 points

Input for DS90CF384A is connected with shielded LVDS cable. Output is connected to RGB interface display. This IC is assembled on separate PCB.

Input LVDS signals pair connected to respective RxIN pins. Input LVDS CLK input are connected to RxCLKIN pins. These LVDS signals are coming from PC motherboard.

Output RGB signals are connected with reference to datasheet (Figure 4. “16 Grayscale” Test Pattern (DS90CF384A)).

0 Sandeep Shinde over 6 years ago in reply to Sandeep Shinde

Prodigy 140 points

LVDS to RGB conversion.pdfSchematic attached.

0 Ikechukwu Anyiam over 6 years ago in reply to Sandeep Shinde

TI__Mastermind 35130 points

Have you checked the mapping between your motherboard and the DS90CF384A? Namely:

RxIN3 = XX, B7, B6, G7, G6, R7, R6
RxIN2 = EN, VS, HS, B5, B4, B3, B2
RxIN1 = B1, B0, G5, G4, G3, G2, G1
RxIN0 = G0, R5, R4, R3, R2, R1, R0

This corresponds to Figure 10 in the datasheet and how you have labeled the output pins in your schematic.

Regards,
I.K.

0 Sandeep Shinde over 6 years ago in reply to Ikechukwu Anyiam

Prodigy 140 points

Thanks for your reply!

I have checked the mapping between motherboard and the DS90CF384A.

It is similar to Figure 10 of datasheet. Please see attachment.

Thanks & Regards,

SandeepPresent mapping.pdf

0 Sandeep Shinde over 6 years ago in reply to Sandeep Shinde

Prodigy 140 points

Display is totally blank. What are the other test points?

0 Ikechukwu Anyiam over 6 years ago in reply to Sandeep Shinde

TI__Mastermind 35130 points

Have you checked if the device is actually outputting anything? What does the output clock (RxCLK OUT) look like on an oscilloscope?

Regards,
I.K.

0 Sandeep Shinde over 6 years ago in reply to Ikechukwu Anyiam

Prodigy 140 points

Please see attached image of RxCLK OUT.LCD_DOTCLK.pdf

0 Darryl Jeong over 6 years ago in reply to Sandeep Shinde

TI__Expert 4210 points

Hi Sandeep,
I looked at the scope shot you provided but this doesn't make sense to me. Why is the RxCLK OUT clock toggling from 1.2V to 2.1V. The 384 output should toggle 0 to 3.3V (nom).

0 Ikechukwu Anyiam over 6 years ago

TI__Mastermind 35130 points

Hi Sandeep,

In addition, I just noticed that you are not terminating the LVDS inputs in your schematic. The DS90CF384A requires 100 ohm differential termination resistors on the LVDS data lanes and LVDS clock lane, as close to the device inputs as possible: