Request for Schematic Review – ADV7280BCPZ Circuit

Hi,

   Please crosscheck your schematic against our reference one at  ADV7281/ADV7281-M / ADV7281-MA Design Support Files 

Thanks,

Poornima

Hi,

    Please refer to the threads below to get the details about the crystal, clock, and hardware connections.

 How Do I Use an External Oscillator to Clock the ADV728x ? 

 Explanation As To Why the Crystal Does Not Oscillate on ADV7182 or ADV728x Systems After Powerup 

 How to get Crystal Clock output on GPIO pin of ADV728x 

 How to Detect That the Crystal is Working Correctly on the ADV7182/ADV728x 

   Regarding hardware connections,

1. Please check exposed pad is to be tied to ground since many people miss this.

2. Keep a solid ground under the part

3. Keep PVDD_1V8 very clean since PVDD is very important maintaining video stability.

    Ideally it should be ferrite bead isolated from other supplies. The data sheet reference schematic does not show this which is OK if the PVDD source is very clean. Unfortunately I do not have acceptable hard noise figures to give you.

    First check PVDD noise both high frequency and lower frequencies around the horizontal rates. If noise is coupled into PVDD then the PLL might lose lock and causing image issues.

    Also when routing the analog interface inputs on the PCB, keep track lengths to a minimum. Use 75 Ω trace impedances when possible; trace impedances other than 75 Ω increase the chance of reflections. The divider network traces will then be very short and have effect on reflection.

    Expert created a simple tool PCB Trace Impedance Calculator  for impedance calculations.  You should use your layout tool for better results.  For 75 Ohm board would came up with 5 mil width, 1.4 mil thickness, 7 mil prepreg giving 75 Ohm impedance PCB.  spacing of 10 mils gets Zd = 131 Ohm.  

Thanks,

Poornima