Rainbow Electronics MAX9508 - Manual (Page 12)

MAX9508
Active-Detect Mode
The active video-detect circuit slices the CVBSIN signal
at 4.7% of the power supply (155mV for a 3.3V supply).
If the transitions occur at a rate of 14kHz or higher, a
video signal is present. When the MAX9508 detects a
video signal with sync at the CVBSIN input, the control
logic enters the active-detect mode and enables the
load sense circuitry (Figure 3). The supply current is
typically 17µA.
If an output load is not connected to any amplifier, the
MAX9508 remains in active-detect mode. Eight times per
second, each load-sense circuit checks for a load by
connecting an internal 15kΩ pullup resistor to the output
for 1ms. If the output is pulled up, then no load is pre-
sent. If the output stays low, a load is connected.
Video Filter Amplifier with SmartSleep and
Bidirectional Video Support
12 ______________________________________________________________________________________
CVBS 1
CIN
YIN
EXTCVBSIN
COUT
YOUT
CVBSOUT1
CVBSIN
CVBSOUT2
LPF
GND
+3.3V
V DD
CLAMP
OFF
LOAD SENSE
6dB
75Ω
75Ω
LPF
BUFFER
LOAD SENSE
BUFFER
BUFFER
6dB
LOAD SENSE
6dB
75Ω
LOAD SENSE
6dB
75Ω
LPF
MAX9508
17µA
SVIDEO
CHROMA
SVIDEO
LUMA
NO
LOADS
CURRENT
DAC
CURRENT
DAC
VIDEO SIGNAL
PRESENT
CURRENT
DAC
VIDEO ENCODER
SHDN
INT/EXT
ACTIVE VIDEO
DETECT
SMARTSLEEP CONTROL
LOGIC
+3.3V
+3.3V
0
TO
50mV
OFF
OFF
OFF
OFF
OFF
OFF
OFF
OFF
OFF
OFF
CVBS 2
Figure 3. Active-Detect Mode with No Output Loads