Video Filter Amplifier with SmartSleep

and Y/C Mixer Circuit

______________________________________________________________________________________

11

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 14.3kHz 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 ampli-

fier 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

LOAD SENSE

6dB

75

Ω

75

Ω

LPF

BUFFER

LOAD SENSE

BUFFER

6dB

LOAD SENSE

6dB

75

Ω

LOAD SENSE

6dB

75

Ω

MAX9512

CHROMA

LUMA

NO

LOADS

CURRENT

DAC

CURRENT

DAC

VIDEO ENCODER

OFF

OFF

OFF

OFF

OFF

OFF

OFF

OFF

OFF

CVBS2

SHDN

SMARTSLEEP

CONTROL

LOGIC

ACTIVE VIDEO

DETECT

+3.3V

+3.3V

17

μA

VIDEO SIGNAL

PRESENT

0

TO

50mV

Figure 3. Active-Detect Mode with No Output Loads