AD9884A
PIN FUNCTION DESCRIPTIONS (continued)
Pin Name
REFOUT
Function
Internal Reference Output
Output from the internal 1.25 V bandgap reference. This output is intended to drive relatively light loads. It can
drive the AD9884A Reference input directly, but should be externally buffered if it is used to drive other loads as
well. The absolute accuracy of this output is
±
4%, and the temperature coefficient is
±
50 ppm, which is adequate
for most AD9884A applications. If higher accuracy is required, an external reference may be employed. If an exter-
nal reference is used, tie this pin to ground through a 0.1
µF
capacitor.
Reference Input
The reference input accepts the master reference voltage for all AD9884A internal circuitry (+1.25 V
±
10%). It
may be driven directly by the REFOUT pin. Its high impedance presents a very light load to the reference source.
This pin should be bypassed to Ground with a 0.1
µF
capacitor.
External Filter Connection
For proper operation, the pixel clock generator PLL requires an external filter. Connect the filter shown in
Figure
10 to this pin. For optimal performance, minimize noise and parasitics on this node.
ANALOG INTERFACE
REFIN
FILT
POWER SUPPLY
V
D
V
DD
Main Power Supply
These pins supply power to the main elements of the circuit. It should be as quiet and filtered as possible.
Digital Output Power Supply
A large number of output pins (up to 52) switching at high speed (up to 140 MHz) generates a lot of power supply
transients (noise). These supply pins are identified separately from the V
D
pins so special care can be taken to
minimize output noise transferred into the sensitive analog circuitry. If the AD9884A is interfacing with lower-
voltage logic, V
DD
may be connected to a lower supply voltage (as low as 2.5 V) for compatibility.
Clock Generator Power Supply
The most sensitive portion of the AD9884A is the clock generation circuitry. These pins provide power to the
clock PLL and help the user design for optimal performance. The designer should provide “quiet,” noise-free
power to these pins.
Ground
The ground return for all circuitry on chip. It is recommended that the AD9884A be assembled on a single solid
ground plane, with careful attention to ground current paths. See the Design Guide for details.
PV
D
GND
–8–
REV. C
ROCHESTER [ Rochester Electronics ]
