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ISL59831

Single Supply Video Driver with Reconstruction Filter and Charge Pump

Renesas Electronics 

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 4th 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 2.8VP-P video signal into a

150 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

0VP-P to 1.4VP-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

CPVEEOUT and VEEIN. See “Block Diagram/Typical

Application Circuit” on page 2 for further information.

The CPVEEOUT Pin

CPVEEOUT 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.

FN6266 Rev 0.00

Mar 29, 2007

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

150 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 150 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 75 cables,

will drive 220pF loads in parallel with 150 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 GND will disable the amplifier. The

amplifier will be enabled when the signal at ENABLE pin is 2V

above GND.

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