Rainbow Electronics MAX9512 - Manual (Page 11)

MAX9512
Video Filter Amplifier with SmartSleep
and Y/C Mixer Circuit
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Active-Detect Mode
The active video detect circuit slices the YIN 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, then
a video signal is present. When the MAX9512 detects
a video signal with sync at the YIN 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
MAX9512 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.
Full-Operation Mode
If a load is connected to an output, the corresponding
filter and amplifier turn on and remain on until the out-
put load is disconnected. In full-operation mode,
SmartSleep intelligently reduces the supply current
based on the input signal presence and output loading.
Figures 4 and 5 show which portions of the MAX9512
turn on and which remain off with different load configu-
rations. In Figure 4, both filters and the Y/C mixer turn
on to generate the composite video signal for the
amplifier connected to CVBSOUT1. In Figure 5, only the
luma filter turns on, and the Y/C mixer stays off.
When an amplifier is on, it continually checks if the load
has been disconnected by detecting if the amplifier
output is sourcing current during a horizontal line time.
If no sourcing current is detected within one horizontal
line time (approximately 64µs), the load has been dis-
connected and the amplifier returns to active-detect
mode. If, at any time, the input video signal is removed,
the MAX9512 returns to standby mode.
If the SmartSleep feature is not activated and the part is
not in shutdown, then the filters and amplifiers com-
pletely turn on, regardless of whether there is a video
signal at the CVBSIN input and whether there are loads
connected at the outputs.
CVBS1
CIN
YIN
COUT
YOUT
CVBSOUT1
CVBSOUT2
LPF
GND
+3.3V
V
DD
LOAD SENSE
6dB
75 Ω
75 Ω
LPF
BUFFER
LOAD SENSE
BUFFER
6dB
LOAD SENSE
6dB
75 Ω
LOAD SENSE
6dB
75 Ω
MAX9512
17 µA
CHROMA
LUMA
NO
LOADS
CURRENT
DAC
CURRENT
DAC
VIDEO ENCODER
VIDEO SIGNAL
PRESENT
OFF
OFF
OFF
OFF
OFF
OFF
OFF
OFF
OFF
CVBS2
SHDN
SMARTSLEEP
CONTROL
LOGIC
ACTIVE VIDEO
DETECT
+3.3V
Figure 3. Active-Detect Mode with No Output Loads