ISL59833 Datasheet, PDF (12/15 Pages) Intersil Corporation – 200MHz Single Supply Video Driver With Charge Pump

ISL59833
with proprietary output stage topology, keeping the output
impedance low over a wide frequency range and making it
possible to easily and effectively drive relatively heavy
capacitive loads (see Figure 11).
THE CHARGE PUMP
The ISL59833 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 110MHz 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. This generates a negative rail
of about -1.6V with a low amplitude ripple voltage from the
charge pump action. Some of this ripple is coupled into the
output signals at a very low amplitude, as seen in Figure 22.
The ripple on the outputs is typically well below the noise
floor of the signal.
There are two ways to further reduce the output supply
noise:
• Add a 120Ω bead in series between V_CC and DV_CC. This
reduces the coupling between the charge pump and the
analog amplifier supplies.
• Add a 20pF capacitor between the back load 75Ω resistor
and ground (see “ISL59833 + DC-Restore Solution” on
page 10). This will attenuate frequencies above 100MHz.
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” on page 14.
I_N+
I_N-
BIAS
OUT
FIGURE 27. SIMPLIFIED SCHEMATIC
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FN6334.1
March 5, 2007