Detailed Description

The MAX9502 filters and amplifies the video DAC output

in applications such as digital still cameras and mobile

phones. The MAX9502 consists of a lowpass filter and

an output video buffer capable of driving a standard 150Ω

video load to ground. The MAX9502G output buffer pro-

vides a fixed gain of +6dB, while the MAX9502M output

buffer provides a fixed gain of +12dB.

Filter

The MAX9502 contains a 4th-order Chebyshev recon-

struction filter. The Chebyshev-type response features a

0.4dB flat passband for NTSC and PAL signals. The stop-

band offers 55dB (typ) of attenuation at 27MHz and above

(see the Typical Operating Characteristics).

Output Amplifier

The MAX9502G features a +6dB gain, while the

MAX9502M features a +12dB gain. Operating from a 2.5V

to 3.0V supply, the output amplifier is able to drive a 2V

signal into a 150Ω video load to ground. Operating from a

3.0V to 3.6V supply, the output amplifier is able to drive a

2.4VP-P signal into a 150Ω video load to ground. The out-

put is typically offset 110mV above ground to guarantee

linear operation of the amplifier. The MAX9502 output only

sources current; all loads should be connected to ground.

Short-Circuit Protection

The MAX9502 typical application circuit includes a 75Ω

back-termination resistor that limits short-circuit currents

for an external short applied at the video output. The

MAX9502 features internal output short-circuit protection

to prevent device damage in prototyping and applications

where the amplifier output can be directly shorted.

Short-circuit protection activates if the output is short-

circuited and the output current exceeds 95mA. During

short-circuit protection, the output of the MAX9502 is shut

off for 12μs and then turns on for 0.8μs. If the short is still

present, the MAX9502 output shuts off again. Extended

short circuits result in a pulsed output. The device

resumes normal operation after the short is removed.

Applications Information

Input Considerations

The MAX9502 input is DC-coupled. When the supply volt-

age is between a 2.5V and 3V supply, the input voltage

range extends from ground to 1.05V for the MAX9502G

and from ground to 0.525V for the MAX9502M. When the

supply voltage is between 3V and 3.6V, the input voltage

range extends from ground to 1.2V for the MAX9502G and

from ground to 0.6V for the MAX9502M. The MAX9502G

accepts a composite video signal with a sync tip from 0

to 50mV and the MAX9502M accepts a composite video

signal with a sync tip from 0 to 25mV. A typical current-

output DAC that operates from a single supply usually

creates a composite video signal with a sync tip very

close to ground. Hence, the DAC output can be directly

connected to the MAX9502 input. Keep the board trace as

short as possible to minimize parasitic stray capacitance

and prevent unintentional high-frequency attenuation.

Output Considerations

The MAX9502 output must be DC-coupled. No

AC-coupling capacitors are allowed. The MAX9502 con-

nects directly to the video cable through a 75Ω series

backtermination resistor. The other end of the cable

should be properly terminated with a 75Ω resistor as well.

Because of this configuration, the peak-to-peak amplitude

as well as the DC level of the signal is divided by two. The

MAX9502 output signal is level-shifted up so the sync tip

is around 110mV.

Power-Supply Bypassing and Layout

Considerations

The MAX9502 operates from a single-supply voltage

down to 2.5V, allowing for low-power consumption.

Bypass VCC to GND with a 0.1μF capacitor. Place all

external components as close to the device as possible.

MAX9502

2.5V Video Amplifier with Reconstruction Filter

www.maximintegrated.com

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