ISL59830A Datasheet, PDF (12/15 Pages) Intersil Corporation – True Single Supply Video Driver With Power Down

ISL59830A
The Charge Pump
The ISL59830A 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.
There are two options to reduce the output supply noise.
• Add a 120Ω bead in series between V_CC and DV_CC to
further reduce ripple.
• Add a 20pF capacitor between the back load 75Ω resistor
and ground (see the ISL59830A + DC-Restore Solution
schematic on page 10).
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 VREF 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 the outgoing signal. The charge
pump provides sufficient bottom room to accommodate the
shifted signal.
Note: The VREF input is the common point of the 3 amps
minus input resistors. Any common resistance on VREF
input will share the voltage induced on it with all the other
amps, so using a resistor source to get offset will cause
cross talk and gain change for the offset for all amps and
amp +input gain change. Offset on the VREF pin must be
low impedance to prevent gain error and cross talk. A
transistor emitter follower should work like an NPN
MMBT3904 with the emitter connected to the VREF pin and
1k pull down to V- with 1µF cap bypass to ground and the
collector to V+ and base to V offset source. If better tempco
is needed then a diode may be used in series with the pot to
ground. A 499W resistor may be added in series with the
collector to prevent damage when testing.
See the Block Diagram on page 9.
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 ISL59830A 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 ISL59830A 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 ISL59830A, generating a negative rail internally, is
ideally suited for NTSC video with its accompanying
negative-going sync signals; easily handled by the
ISL59830A without the need of an additional supply as the
ISL59830A 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 ISL59830A. Specifically, this
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FN6233.3
September 26, 2006