ISL59119 Datasheet, PDF (8/10 Pages) Intersil Corporation – Triple Channel Video Driver with LPF

ISL59119
Typical Performance Curves (Continued)
JEDEC JESD51-7 HIGH EFFECTIVE THERMAL
CONDUCTIVITY TEST BOARD
1.0
909mW
0.8
0.6
435mW
0.4
0.2
θ_{JA =S+O2T302°3C-6/W}
0
0
25
50
75 85 100 125 150
AMBIENT TEMPERATURE (°C)
FIGURE 25. PACKAGE POWER DISSIPATION vs AMBIENT
TEMPERATURE
JEDEC JESD51-3 LOW EFFECTIVE THERMAL
CONDUCTIVITY TEST BOARD
0.7
0.6 _625mW
0.5
0.4
391mW
0.3
0.2
0.1
θ_{JA =} ^{S+2O5T62°3C-/6W}
0
0
25
50
75 85 100 125 150
AMBIENT TEMPERATURE (°C)
FIGURE 26. PACKAGE POWER DISSIPATION vs AMBIENT
TEMPERATURE
Application Information
The ISL59119 is a single-supply rail-to-rail triple (one
S-video channel and one composite channel) video amplifier
with internal sync tip clamps, a typical -3dB bandwidth of
8MHz and slew rate of about 25V/µs. This part is ideally
suited for applications requiring high composite and S-video
performance with very low power consumption. As the
performance characteristics and features illustrate, the
ISL59119 is optimized for portable video applications.
Internal Sync Clamp
Embedded video DACs typically use ground as their most
negative supply. This places the sync tip voltage at a
minimum of 0V. Presenting a 0V input to most single supply
amplifiers will saturate the output stage of the amplifier
resulting in a clipped sync tip and degraded video image.
The ISL59119 features an internal sync clamp and offset
function that level shifts the entire video signal to the
optimum level before it reaches the amplifiers’ input stage.
These features also help avoid saturation of the output stage
of the amplifier by setting the signal closer to the best
voltage range.
The simplified block diagram on page 1 shows the basic
operation of the ISL59119’s sync clamp. The Y and CVBS
inputs’ AC-coupled video sync signal is pulled negative by a
current source at the input. When the sync tip goes below
the comparator threshold, the comparator output goes high,
pulling up on the input through the diode, forcing current into
the coupling capacitor until the voltage at the input is again
0V, and the comparator turns off. This forces the sync tip
clamp to always be 0V, setting the offset for the entire video
signal. The C-Channel is slaved to the Y-Channel and
clamped to a 500mV level at the input.
Figure 27 shows the setup for testing the clamp’s response
to a large step response at the input.
1Hz SQUARE WAVE
500Ω
NTSC VIDEO
75Ω
CH1
CH2
0.1µF
75Ω
ISL59119
OUTPUT
150Ω
FIGURE 27. DC STEP RESPONSE CIRCUIT
Once the signals are clamped at the input they are level
shifted by +65mV before being amplified by a gain of x2.
The Sallen Key Low Pass Filter
The Sallen Key is a classic low pass configuration. This
provides a very stable low pass function, and in the case of
the ISL59119, a three-pole roll-off at 8MHz. The three-pole
function is accomplished with an RC low pass network placed
in series with and before the Sallen Key. The first pole is
formed by an RC network, with poles two and three generated
with a Sallen Key, creating a nice three-pole roll-off at 8MHz.
Output Coupling
The ISL59119 can be AC or DC coupled to its output. When
AC coupling, a 220µF coupling capacitor is recommended to
ensure that low frequencies are passed, preventing video
“tilt” or “droop” across a line.
The ISL59119’s internal sync clamp makes it possible to DC
couple the output to a video load, eliminating the need for
any AC coupling capacitors, saving board space, cost, and
eliminating any “tilt” or offset shift in the output signal. The
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FN6319.1
January 28, 2008