Rainbow Electronics MAX9519 - Manual (Page 7)

Detailed Description
The MAX9519 is an ultra-small, standard-definition video
filter amplifier with automatic shutdown. Automatic shut-
down circuitry provides intelligent power management
by disabling the filter and output amplifier in the
absence of an input video signal and/or output load.
Figure 1 shows automatic shutdown.
An internal reconstruction filter smooths the steps and
reduces the spikes on the video signal from the video
digital-to-analog converter. The reconstruction filter typ-
ically has ±1dB passband flatness to 9MHz and typi-
cally 48.5dB of attenuation at 27MHz. The MAX9519
has an internal fixed gain of 4V/V and expects a nomi-
nal full-scale video input signal of 0.5V
P-P .
Automatic Shutdown
The MAX9519 automatic shutdown circuitry reduces
power consumption when there is no active video input
signal or an output load. In shutdown, the supply cur-
rent is reduced to 1.8µA. The video amplifier only turns
on when both an active video input signal and an out-
put load are present.
The MAX9519 slices the IN signal at 2.4% of the power
supply (80mV for a 3.3V supply). If the transitions occur
at a rate of 7.3kHz or higher, a video signal is present.
When the MAX9519 detects a video signal with sync at
the input, the control logic enters the active-detect mode
and enables the load sense circuitry (Figure 2). The sup-
ply current increases from 1.8µA to 5.4µA typically.
If an output load is not connected to the amplifier, the
MAX9519 remains in active-detect mode. Eight times
per second, the load-sense circuit checks for a load by
connecting an internal 15kΩ pullup resistor to the out-
put for 1ms. If the output is pulled up, no load is pre-
sent. If the output stays low, a load is connected.
If the input video signal is present and a load is con-
nected to the output, the filter and amplifier turn on and
remain on until the output load is disconnected.
Automatic shutdown intelligently reduces the supply
current based on the input signal presence and output
loading (Figure 3).
When the amplifier is on, it continually checks if the
load has been disconnected by detecting if the amplifi-
er output is sourcing current during a horizontal line
time. If no sourcing current is detected within one hori-
zontal line time (approximately 64µs), the load has
been disconnected and the amplifier returns to active-
detect mode. If, at any time, the input video signal is
removed, the MAX9519 returns to standby mode.
MAX9519
1mm x 1mm Video Filter Amplifier with
Automatic Shutdown and 4V/V Gain
_______________________________________________________________________________________ 7
CURRENT
DAC
VIDEO ENCODER
VIDEO SIGNAL
PRESENT
A V = 4V/V
OUT
NO LOAD
IN
BUFFER
LPF
AUTOMATIC
SHUTDOWN
CONTROL LOGIC
MAX9519
V DD
+3.3V
5.4 μA
75 Ω
GND
0
TO
25mV
0.5V P-P VIDEO
Figure 2. Active-Detect Mode