19-0553; Rev 0; 5/06
Loss-of-Sync Alarm
General Description
The MAX7461 single-channel loss-of-sync alarm (LOS)
provides composite video sync detection in NTSC,
PAL, and SECAM standard-definition television (SDTV)
systems. The MAX7461’s advanced detection circuitry
delivers robust performance by preventing false loss-
of-sync alarms due to noise. The device accepts an
AC-coupled composite (CVBS), luma (Y), or any other
video signal with sync, and outputs a logic-level signal.
The open-drain
LOS
output is low when no sync is
detected and high impedance when sync is detected.
The device operates from a single +5V supply.
The MAX7461 is available in a 5-pin SOT23 package
and is specified for operation over the -40°C to +85°C
temperature range.
♦
Loss-of-Sync Alarm Output
♦
Robust Performance in Noisy Environments
♦
Wire-OR Alarm Output
♦
NTSC, PAL, and SECAM
♦
Small 5-Pin SOT23 Package
Features
♦
Accepts CVBS, Y, or Any Other Video with Sync
MAX7461
Ordering Information
PART
MAX7461EUK
TEMP RANGE
-40°C to +85°C
PIN-
PACKAGE
5 SOT23-5
PACKAGE
CODE
U5-2
Applications
Security Systems
Automotive Rear Seat Entertainment (RSE)
Systems
Consumer Electronics
IN
1
Pin Configuration
TOP VIEW
5
V
CC
GND 2
MAX7461
GND 3
4
LOS
SOT23-5
Functional Diagram
+5V
0.1µF
V
CC
5
V
CC
SYNC
SLICE
LEVEL
MAX7461
RO
1kΩ
SYNC
DETECTOR
SYNC
LOS
FILTER
LOS
4
C
IN
0.1µF
75Ω
IN
1
CLAMP
LPF
GND 3
________________________________________________________________
Maxim Integrated Products
1
For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at
1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com.
Loss-of-Sync Alarm
MAX7461
ABSOLUTE MAXIMUM RATINGS
V
CC
to GND ..............................................................-0.3V to +6V
LOS
to GND..............................................................-0.3V to +6V
IN to GND.................-0.3V to the lower of +6V and (V
CC
+ 0.3V)
Continuous Power Dissipation (T
A
= +70°C)
5-Pin SOT23-5 (derate 7.1mW/°C above +70°C) ......571.0mW
Maximum Current Into Any Pin .........................................±50mA
Operating Temperature Range
MAX7461EUK ...................................................-40°C to +85°C
Storage Temperature Range .............................-65°C to +150°C
Lead Temperature (soldering, 10s) .................................+300°C
Junction Temperature ......................................................+150°C
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional
operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to
absolute maximum rating conditions for extended periods may affect device reliability.
ELECTRICAL CHARACTERISTICS
(V
CC
= +4.5V to +5.5V, GND = 0, C
IN
= 0.1µF, RO = 500Ω, T
A
= -40°C to +85°C, unless otherwise noted. Typical values are at T
A
=
+25°C.)
PARAMETER
AC CHARACTERISTICS
Minimum Input Sync Height
Maximum Input Voltage
LOS Release Time
LOS Detect Time
DIGITAL CHARACTERISTICS
Output Low Voltage
Logic High Leakage Current
POWER REQUIREMENTS
Supply Voltage
Supply Current
Power-Supply Noise Immunity
V
CC
I
CC
V
PSNI
0 to 5MHz sinusoid on V
CC
(Note 4)
4.5
5.0
1.7
200
5.5
2.2
V
mA
mV
P-P
V
OL
I
OLEAK
I
SINK
= 10mA
0.4
1
V
µA
V
IN-MIN
V
IN-MAX
t
RT
t
DT
AC-coupled (Note 1)
AC-coupled
(Note 2)
(Note 3)
2.4
1.7
1.9
2.2
3.4
2.7
4.9
105
130
mV
P-P
V
P-P
ms
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
Note 1:
Minimum input sync height is the voltage above which
LOS
is guaranteed to be in high-impedance mode after the maximum
LOS time-constant time.
Note 2:
LOS release time is the time that the video input must be continuously present before
LOS
goes high (inactive state).
Note 3:
The LOS detect time is the time that the video input must be continuously absent before
LOS
goes low (active state).
Note 4:
The MAX7461
LOS
output is accurate with a power-supply noise level below V
PSNI
.
2
_______________________________________________________________________________________
Loss-of-Sync Alarm
MAX7461
Typical Operating Characteristics
(V
CC
= 5V, GND = 0, C
IN
= 0.1µF, RO = 10kΩ, T
A
= +25°C, unless otherwise noted.)
CVSB LOS ALERT TRANSIENT
MAX7461 toc01
LOS DETECT TIME
vs. SUPPLY VOLTAGE
MAX7461 toc02
LOS RELEASE TIME
vs. SUPPLY VOLTAGE
MAX7461 toc03
3.0
4.0
2.5
TIME (ms)
TIME (ms)
4.5
4.7
4.9
5.1
5.3
5.5
IN
500mV/div
3.5
2.0
3.0
LOS
5V/div
1.5
2.5
1.0
t = 10ms/div
SUPPLY VOLTAGE (V)
2.0
4.5
4.7
4.9
5.1
5.3
5.5
SUPPLY VOLTAGE (V)
SYNC HEIGHT LOS ALERT THRESHOLD
vs. SUPPLY VOLTAGE
MAX7461 toc04
SUPPLY CURRENT
vs. TEMPERATURE (CVBS INPUT)
MAX7461 toc05
0.20
2.0
0.15
SYNC HEIGHT (V)
I
CC
(mA)
4.5
4.7
4.9
5.1
5.3
5.5
1.9
0.10
1.8
0.05
1.7
0
SUPPLY VOLTAGE (V)
1.6
-40
-20
0
20
40
60
80
TEMPERATURE (°C)
_______________________________________________________________________________________
3
Loss-of-Sync Alarm
MAX7461
Pin Description
PIN
1
2, 3
NAME
IN
GND
FUNCTION
Video Input. Accepts CVBS, luma (Y), or any video input with sync. AC-couple IN with a series 0.1µF
capacitor.
Ground
Loss-Of-Sync Output (Open Drain).
LOS
is in high impedance when sync pulses are detected, and is
pulled low when no horizontal sync signal is detected for more than the LOS detect time.
LOS
returns
high when sync pulses are detected for more than the LOS release time. Connect a 1kΩ pullup resistor
from
LOS
to V
CC
.
Power-Supply Input. Bypass to GND with a 0.1µF capacitor.
4
LOS
5
V
CC
Detailed Description
The MAX7461 single-channel LOS alarm is ideal for any
video system needing to verify the presence of a video
source. The device accepts an AC-coupled CVBS, Y,
or any video signal with sync, and pulls
LOS
low when
no composite sync signal is detected for more than the
LOS detect time (3.4ms, typ) at the input (IN).
Applications Information
Input Considerations
Use 0.1µF ceramic capacitors to AC-couple the input.
The input cannot be DC-coupled. The input capacitor
stores a DC level so that the video signal is clamped to
an appropriate DC voltage for proper sync detection.
Clamp
The MAX7461 features an input clamp that corrects any
DC shift, on a line-by-line basis. The external AC-cou-
pling capacitor provides DC isolation for the input.
Power-Supply Bypassing
Careful PC board layout is important for optimal system
performance. Do not use wire-wrapped boards or
breadboards. When possible, use a multilayer board
with a dedicated low-inductance ground plane and
supply plane. Connect all GND inputs to a single
ground plane and V
CC
to a single-supply plane.
Bypass V
CC
to GND with a 0.1µF capacitor.
Lowpass Filter
The MAX7461 integrates a lowpass filter for enhanced
sync detection. The lowpass filter prevents false sync
detection by reducing color burst, chroma, and noise.
Wired-OR Application
The
LOS
open-drain output allows the MAX7461 to be
used in wired-OR applications as shown in the automo-
tive RSE typical application diagram of Figure 1.
Sync Detector/LOS Filter
The sync detector looks for sync pulses greater than
the minimum sync voltage (0.13V
P-P
). If the detector
does not detect any sync pulses for 3.4ms (typ), the
LOS filter pulls
LOS
low. After detecting sync for at
least 2.2ms (typ), the LOS filter returns
LOS
to a high-
impedance state.
LOS
is an open-drain output.
Connect a 1kΩ pullup resistor between
LOS
and V
CC
.
Chip Information
PROCESS: BiCMOS
Power-On Reset (POR)
At power-up,
LOS
is pulled low and the MAX7461
checks for 2.2ms (typ) of valid sync pulses before
releasing
LOS. LOS
remains high impedance while a
valid sync signal is detected at the input.
4
_______________________________________________________________________________________
Loss-of-Sync Alarm
MAX7461
V
CC
1kΩ
µC
MAX7461
0.1µF
TV
TUNER
75Ω
MONITOR 1
MAX7461
0.1µF
RGB VIDEO SOURCE
SWITCH
MATRIX
AND
PROCESSING
75Ω
MONITOR N
MAX7461
0.1µF
CAMERA
75Ω
Figure 1. Automotive RSE System
_______________________________________________________________________________________
5
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