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ADV7121/ADV7122
–6–
REV. B
PIN FUNCT ION DE SCRIPT ION
Pin
Mnemonic
Function
BLANK
*
Composite blank control input (T T L compatible). A logic zero on this control input drives the analog outputs,
IOR, IOB and IOG, to the blanking level. T he
BLANK
signal is latched on the rising edge of CLOCK . While
BLANK
is a logical zero, the R0–R9, G0–G9 and R0–R9 pixel inputs are ignored.
Composite sync control input (T T L compatible). A logical zero on the
SYNC
input switches off a 40 IRE
current source. T his is internally connected to the IOG analog output.
SYNC
does not override any other
control or data input, therefore, it should only be asserted during the blanking interval.
SYNC
is latched on the
rising edge of CLOCK .
If sync information is not required on the green channel, the
SYNC
input should be tied to logical zero.
Clock input (T T L compatible). T he rising edge of CLOCK latches the R0–R9, G0–G9, B0–B9,
SYNC
and
BLANK
pixel and control inputs. It is typically the pixel clock rate of the video system. CLOCK should be
driven by a dedicated T T L buffer.
Red, green and blue pixel data inputs (T T L compatible). Pixel data is latched on the rising edge of CLOCK .
R0, G0 and B0 are the least significant data bits. Unused pixel data inputs should be connected to either the
regular PCB power or ground plane.
IOR, IOG, IOB Red, green, and blue current outputs. T hese high impedance current sources are capable of directly driving a
doubly terminated 75
coaxial cable. All three current outputs should have similar output loads whether or not
they are all being used.
FS ADJUST
Full-scale adjust control. A resistor (R
SET
) connected between this pin and GND, controls the magnitude of the
full-scale video signal. Note that the IRE relationships are maintained, regardless of the full-scale output current.
T he relationship between R
SET
and the full-scale output current on IOG (assuming I
SYNC
is connected to IOG)
is given by:
R
SET
(
)
= 12,082
×
V
REF
(V)/IOG (mA)
T he relationship between R
SET
and the full-scale output current on IOR, IOG and IOB is given by:
IOG* (mA)
= 12,082
×
V
REF
(V)/R
SET
(
) (
SYNC
being asserted)
IOR, IOB (mA)
= 8,628
×
V
REF
(V)/R
SET
(
)
T he equation for IOG will be the same as that for IOR and IOB when
SYNC
is not being used, i.e.,
SYNC
tied permanently low. For the ADV7121, all three analog output currents are as described by:
IOR, IOG, IOB (mA)
= 7,969
×
V
REF
(V)/R
SET
(
)
COMP
Compensation pin. T his is a compensation pin for the internal reference amplifier. A 0.1
μ
F ceramic capacitor
must be connected between COMP and V
AA
.
V
REF
Voltage reference input. An external 1.23 V voltage reference must be connected to this pin. T he use of an
external resistor divider network is not recommended. A 0.1
μ
F decoupling ceramic capacitor should be
connected between V
REF
and V
AA
.
V
AA
Analog power supply (5 V
±
5%). All V
AA
pins on the ADV7121/ADV7122 must be connected.
GND
Ground. All GND pins must be connected.
SYNC
*
CLOCK
R0–R9,
G0–G9,
B0–B9
*
SYNC
and
BLANK
functions are not provided on the ADV7121.