External Crystal issue when STM33H7 LTDC interface used with RGB to HDMI convertor TI TFP410

[VShet.2]

I am using STM32H743IIT6 MCU to drive HDMI display using LTDC peripheral and Texas Instrument TFP410 for RGB to HDMI conversion. Issue I am facing is I use external crystal as clock source then I see disturbance on my HDMI monitor and its display blinks randomly, say screen is proper for some 5-10 sec then it will flicker and turn off and on then again be stable for some time and these repeats. My guess is that some HDMI timing related parameters are not matched and that's why this behavior on monitor. Surprisingly, this issue resolves if I use internal CSI RC oscillator as clock source.  I even tried doing the PCB layout again using an external agency, but same issue persists in that layout as well. What could be the issue here that it works with internal CSI RC clock source and not external crystal ? Please find below related parameters configured in my project. I have also attached my projects CubeMX .ioc file for reference.

1. Clock Source: External Crystal 25MHz
2. FMC: External SDRAM ISSI IS42S32200L-6TL which is 32bit SDRAM
3. LTDC Settings: 1280 x 720p HD resolution @60Hz (Below parameters are as specified in standard without which if I connect to Dell monitor then it gives timing error on screen)

1. LTDC Clock 74.250 MHz
2. 16bit RGB565
3. LTDC data, clock, HSync, VSync, DE signal goes to TI TFP410 IC whose output are then connected with HDMI connector.
4. Horizontal Timings
   1. Active Pixels 1280
   2. Front Porch 110
   3. Sync Width 40
   4. Back Porch 220
   5. Blanking Total 370
   6. Total Pixels 1650
   7. Sync Polarity pos
5. Vertical Timings
   1. Active Lines 720
   2. Front Porch 5
   3. Sync Width 5
   4. Back Porch 20
   5. Blanking Total 30
   6. Total Lines 750
   7. Sync Polarity pos

[VShet.2]

Yes, My probe is 10:1 and all pins are set to Very High state.

[MM..1]

Based on your description, your ext HSE and PLL is unstable, based maybe on unstable power for HSE or bad pcb around crystal etc. Go back to this and try other crystal values 16M 8M 27M...

[VShet.2]

1. I am using 25 MHz crystal from NDK, exact part number is NX3225sa-25.000m-std-crs-2. I use 22pF capacitor with this crystal. I have attached Crystal datasheet as well.

2. Power is delivered from MCU itself through its OSC_IN, OSC_OUT pins. So, what should I check from unstable power?

3. My PCB has 4 layers and crystal is on 1st layer, 2nd layer below that has ground plane, 3rd layer below that has 3.3V supply plane and 4th layer below that has two data lines of external SDRAM interfaced through FMC passes below crystal capacitors

Do you see any issue with this?

[VShet.2 · Accepted solution]

This issue got fixed as I have replaced External Crystal with External Oscillator in my PCB.