Digital Inputs; Xtal And Load Cap Value Selection - Analog Devices Advantiv ADV7619 Hardware User's Manual

UG-237

DIGITAL INPUTS

The following digital inputs on the ADV7619 are 3.3 V inputs that are 5.0 V tolerant:
•
DDCA_SCL
•
DDCA_SDA
•
DDCB_SCL
•
DDCB_SDA
Any noise that gets onto the HS and VS inputs trace will add jitter to the system. Therefore, the trace length should be minimized; and
digital or other high frequency traces should not be run near it.

XTAL AND LOAD CAP VALUE SELECTION

The ADV7619 uses 28.6363 MHz crystal. Figure 78 shows an example of a reference clock circuit for the ADV7619. Special care must be
taken when using a crystal circuit to generate the reference clock for the ADV7619. Small variations in reference clock frequency can
cause auto detection issues and impair the ADV7619 performance.
These guidelines are followed to ensure correct operation:
•
Use the correct frequency crystal, which is 28.6363 MHz. Tolerance should be 50 ppm or better.
•
Know the C for the crystal part number selected. The value of capacitors C1 and C2 must be matched to the C
load
crystal part number in the user's system.
To find C1 and C2, use the following formula:
C1 = C2 = 2(C − C
load stray
where C is usually 2 pF to 3 pF, depending on board traces and C
stray
Example
C = 30 pF, C1 = 50 pF, C2 = 50 pF (in this case, 47 pF is the nearest real-life cap value to 50 pF)
load
C1
47pF
) − C
pg
XTAL
28.63636MHz
C2
47pF
Figure 78. Crystal Circuit
(pin-to-ground-capacitance) is 4 pF for the ADV7619.
pg
Rev. A | Page 194 of 204
Hardware User Guide
for the specific
load