ISL59830 Datasheet, PDF (12/14 Pages) Intersil Corporation – True Single Supply Video Driver

ISL59830
The Charge Pump
The ISL59830 charge pump provides a bottom rail up to
1.65V below ground while operating on a 0V to 3.3V power
supply. The charge pump is internally regulated to one-half
the potential of the positive supply. This internal multi-phase
charge pump is driven by a 160MHz differential ring
oscillator driving a series of inverters and charge storage
circuitry. Each series inverter charges and places parallel
adjoining charge circuitry slightly out of phase with the
immediately preceding block. The overall effect is sequential
discharge and generation of a very low ripple of about 10mV
that is applied to the amplifiers providing a negative rail of up
to -1.65V.
TIME (20ns/DIV)
FIGURE 28. CHARGE PUMP OSCILLATION
The system operates at sufficiently high frequencies that any
related charge pump noise is far beyond standard video
bandwidth requirements. Still, appropriate bypassing
discipline must be observed, and all pins related to either the
power supply or the charge pump must be properly
bypassed. See "Power Supply Bypassing and Printed Circuit
Board Layout" in this section.
The V_REF Pin
Applying a voltage to the V_REF pin simply places that
voltage on what would usually be the ground side of the gain
resistor of the amplifier, resulting in a DC-level shift of the
output signal. Applying 100mV to the Vref pin would apply a
100mV DC level shift to an incoming signal. The charge
pump providing sufficient bottom room to accommodate the
shifted signal.
See Block Diagram on page 8.
The V_EE Pin
The V_EE pin is the output pin for the charge pump. A
voltmeter applied to this pin will display the output of the
charge pump. This pin does not affect the functionality of the
part. One may use this pin as an additional voltage source.
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. We recommend a 0.1µF ceramic
capacitor placed as close to the pin and connected to the
ground plane of the board.
Input, Output, and Supply Voltage Range
The ISL59830 is designed to operate with a single supply
voltage range of from 0V to 3.3V. The need for a split supply
has been eliminated with the incorporation of a charge pump
capable of generating a bottom rail as much as 1.6V below
ground, for a 4.9V range on a single 3.3V supply. This
performance is ideal for NTSC video with its negative-going
sync pulses.
Video Performance
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 ISL59830 for the reduction of output
impedance variation with the current output. This results in
outstanding differential gain and differential phase
specifications of 0.06% and 0.1°, while driving 150Ω at a
gain of +2. Driving higher impedance loads would result in
similar or better differential gain and differential phase
performance.
NTSC
The ISL59830, generating a negative rail internally, is ideally
suited for NTSC video with its accompanying negative-going
sync signals; easily handled by the ISL59830 without the
need of an additional supply as the ISL59830 generates a
negative rail with an internal charge pump referenced at
negative 1/2 the positive supply.
YPbPr
YPbPr signals originating from a DVD player requiring three
channels of very tightly-controlled amplifier gain accuracy
present no difficulty for the ISL59830. Specifically, this
standard encodes sync on the Y channel and it is a negative-
going signal; easily handled by the ISL59830 without the
need of an additional supply as the ISL59830 generates a
negative rail placed at negative 1/2 the positive supply.
Additionally, the Pb and Pr are bipolar analog signals and
the video signals are negative-going; and again easily
handled by the ISL59830.
Driving Capacitive Loads and Cables
The ISL59830, internally-compensated to drive 75Ω cables,
will drive 10pF loads in parallel with 1kΩ with less than 5dB
of peaking. If less peaking is required, a small series resistor,
usually between 5Ω to 50Ω, can be placed in series with the
output. This will reduce peaking at the expense of a slight
closed loop gain reduction. When used as a cable driver,
double termination is always recommended for reflection-
free performance. For those applications, a back-termination
series resistor at the amplifier's output will isolate the
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FN7489.2
August 15, 2005