el4501 Intersil Corporation, el4501 Datasheet - Page 19

• Manufacturer Part Number: el4501
• Description: Video Front End
• Manufacturer: Intersil Corporation

which in turn decreases the reference time and pulse width.
A higher frequency video input requires a lower R
value. The Line Rates vs R
the variation of line rate with R
Slice Mode and Operation with VCRs
Normally the signal source for the EL4501 is assumed to be
clean and relatively noise free. If that is the case, the SLICE
MODE pin (pin 16) should be connected to ground, which
sets the slice level to 50% of the sync tip. Some signal
sources may have excessive video peaking, causing high
frequency video and chroma components to extend below
the black level reference, such as VCR signals which
generate lots of head switching noise. In this case, the
SLICE MODE pin should be connected to logic high which
sets the slice level to a fixed 100mV above the sync tip. Also,
a single pole chroma filter is required at the composite video
input to increase the S/N ratio of the incoming noisy video
signal. When the source impedance is low, typically 75Ω, a
620Ω resistor in series with the source and 470pF capacitor
to ground will form a low pass filter with a roll-off frequency of
about 550kHz. This bandwidth sufficiently attenuates the
3.58MHz (NTSC) or 4.43MHz (PAL) color burst signal and
high frequency spikes, yet passes the sync pulse portion
without appreciable attenuation. The chroma filter will
increase the propagation delay from the composite sync
input to the outputs. Applying a chroma filter, setting the
SLICE MODE pin and FSEL pin to high greatly improve the
noise immunity performance in VCR applications.
Output Drive Capability
The outputs of the sync separator are not designed to drive
heavy loads. For a 5V VDS, if the output is driving 5kΩ load
to ground, the output high voltage is about 4.9V. If the output
is driving 500Ω load, the output high voltage is down to 4.2V.
General
Power Dissipation
With the high output drive capability of the EL4501 video
amplifier, it is possible to exceed the 125°C Absolute
Maximum junction temperature under certain load current
conditions. It is important to calculate the maximum junction
temperature for a given application to determine if load
conditions or package type need to be modified for the
amplifier to remain in its safe operating region.
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FREQ
19
FREQ
performance curve shows
.
FREQ
EL4501
The maximum power dissipation allowed in a package is
determined according to:
where:
• T
• T
• θ
• P
The maximum power dissipation actually produced by an IC
is the product of total quiescent supply current and power
supply voltage, plus the power in the IC due to the load.
Assume no load at the sync separator outputs:
where:
• V
• V
• I
• I
• V
• R
Board Layout
As with any high frequency device, good printed circuit
board layout is necessary for optimum performance. Ground
plane construction is highly recommended. Lead lengths
should be as short as possible. The power supply pin must
be well bypassed to reduce the risk of oscillation. In normal
operation, where the GND pin is connected to the ground
plane, a single 4.7µF tantalum capacitor in parallel with a
0.1µF ceramic capacitor from V
reduce cross talk between the analog signal path and the
embedded sync separator, a separate digital supply pin, V
is included on the EL4501. This pin should be bypassed in a
similar manner to V
may be added in line with the supply connections to both
pins. For good AC performance, parasitic capacitance
should be kept to a minimum. Use of wire wound resistors
should be avoided because of their additional series
inductance.
P
P
DMAX
DMAX
SMAX
SDMAX
JA
AMAX
JMAX
DMAX
S
SD
OUT
L
= Load resistance tied to ground
= Supply voltage
= Thermal resistance of the package
= Digital supply
=
=
= Maximum output voltage
= Maximum supply current
= Maximum junction temperature (125°C)
= Maximum ambient temperature (85°C)
= Maximum power dissipation in the package
V
T
-------------------------------------------- -
= Maximum digital supply current
S
JMAX
×
I
SMAX
Θ
- T
JA
S
AMAX
. For additional isolation a ferrite bead
+
V
SD
×
I
SDMAX
S
to GND will suffice. To
+
(
V
S
- V
OUT
)
×
V
--------------- -
OUT
R
L
SD