ISL59831 Datasheet, PDF (9/11 Pages) Intersil Corporation – Single Supply Video Driver with Reconstruction Filter and Charge Pump

ISL59831
Description of Operation and Application
Information
Theory of Operation
The ISL59831 is a single supply video driver with a
reconstruction filter and an on-board charge pump. It is
designed to drive SDTV displays with luma (Y) or composite
video (CV) signals. The input signal can be AC-coupled or
DC-coupled. When AC-coupled, the sync tip clamp sets the
blank level to ground at the output. The ISL59831 is capable
of driving two AC-coupled or DC-coupled standard video
loads and has a 4^th order Butterworth reconstruction filter
with nominal -3dB frequency set to 9.1MHz, providing 44dB
of attenuation at 27MHz. The ISL59831 is designed to
operate with a single supply voltage range ranging from 3.0V
to 3.6V. This eliminates the need for a split supply with the
incorporation of a charge pump capable of generating a
bottom rail as much as 1.9V below ground; providing a 5.2V
range on a single 3.3V supply. This performance is ideal for
NTSC video with negative-going sync pulses.
Output Amplifier
The ISL59831 output amplifier provides a gain of +6dB. The
output amplifier is able to drive a 2.8V_P-P video signal into a
150Ω load to ground.
The output is a highly-stable, low distortion, low power, high
frequency amplifier capable of driving moderate capacitive
loads.
Input/Output Range
The ISL59831 has a recommended dynamic input range of
0V_P-P to 1.4V_P-P. This allows the device to handle the
maximum possible video signal input. As the input signal
moves outside the specified range, the output signal will
exhibit increasingly higher levels of harmonic distortion. As
the load resistance becomes lower, the current drive
capability of the device will be challenged and its ability to
drive close to each rail is reduced.
The Charge Pump
The ISL59831 charge pump provides a bottom rail up to
1.9V below ground while operating on a 3.0V to 3.6V power
supply. The charge pump is internally regulated and is driven
by an internal 15MHz clock.
To reduce the noise on the power supply generated by the
charge pump, connect a low pass RC-network between
CPVEE_OUT and VEE_IN. See “Block Diagram/Typical
Application Circuit” on page 2 for further information.
The CPVEE_OUT Pin
CPVEE_OUT is the output pin for the charge pump. Keep in
mind that the output of this pin is generated by the internal
charge pump and a fully regulated supply that must be
properly bypassed. Bypass this pin with a 0.1µF ceramic
capacitor placed as close to the pin and connected to the
ground plane of the board.
Video Performance
DIFFERENTIAL GAIN/PHASE
For good video performance, an amplifier is required to
maintain the same output impedance and the same
frequency and phase response as DC levels are changed at
the output. This is especially difficult when driving a standard
video load of 150Ω because of the change in output current
with changing DC levels. Special circuitry has been
incorporated into the ISL59831 for the reduction of output
impedance variation with the current output. This results in
outstanding differential gain and differential phase
specifications of 0.04% and 0.35°, while driving 150Ω at a
gain of +2V/V. Driving higher impedance loads would result
in similar or better differential gain and differential phase
performance.
NTSC
The ISL59831, generating a negative rail internally, is ideally
suited for NTSC video with its accompanying negative-going
sync signals.
Driving Capacitive Loads and Cables
The ISL59831, internally-compensated to drive 75Ω cables,
will drive 220pF loads in parallel with 150Ω with less than
1.5dB of peaking.
AC-Coupled Inputs
SYNC TIP CLAMP
The ISL59831 features a sync tip clamp that sets the black
level of the output video signal to ground. This ensures that
the sync-tip voltage level is set to approximately -300mV at
the back-termination resistor of a standard video load. The
clamp is activated whenever the input voltage falls below 0V.
The correction voltage required to do this is stored across
the input AC-coupling capacitor. Refer to “Block
Diagram/Typical Application Circuit” on page 2 for a detailed
diagram.
DC-Coupled Inputs
When DC-coupling the inputs ensure that the lowest signal
level is greater than +50mV to prevent the clamp from
turning on and distorting the output. When DC-coupled the
ISL59831 shifts the signal by -550mV from input to output.
Amplifier Disable
The ISL59831 can be disabled and its output placed in a
high impedance state. The turn-off time is around 10ns and
the turn-on time is around 30µs. The turn-on time is greater
in length because extra time is given for the charge pump to
settle before the amplifier is enabled. When disabled, the
amplifier's supply current is reduced to 2µA typically,
reducing power consumption. The amplifier's power-down
can be controlled by standard TTL or CMOS signal levels at
the ENABLE pin. The applied logic signal is relative to the
GND pin. Applying a signal that is less than 0.8V above
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FN6266.0
March 29, 2007