3V Video Amplifier with

Internal Gain and Filter in SC70

6 ______________________________________________________________________________________

Pin Description

Detailed Description

The MAX9680 filters and amplifies the video DAC output

in applications such as mobile phones. The MAX9680

consists of two resistors, an input buffer, lowpass filter,

and output amplifier capable of driving a standard 150I

video load to ground. The output amplifier provides a

fixed gain of 5.17V/V.

The video current DAC imposes a reference voltage,

the reference current for the video current DAC.

Input

The video input should be directly connected to the out-

resistance, is 872I to ground. The output current of the

in the voltage domain.

Video Filter

The filter bandwidth (-3dB) is typically 9MHz, making the

device suitable for standard-definition video signals from

all sources (e.g., broadcast and DVD). Broadcast video

signals are channel limited: NTSC signals have 4.2MHz

bandwidth, and PAL signals have 5MHz bandwidth.

Video signals from a DVD player, however, are not chan-

nel limited; so the bandwidth of DVD video signals can

approach the Nyquist limit of 6.75MHz. Recommendation:

ITU-R BT.601-5 specifies 13.5MHz as the sampling rate

for standard-definition video. Therefore, the maximum

bandwidth of the signal is 6.75MHz. To ease the filtering

requirements, most modern video systems oversample

by two times, clocking the video current DAC at 27MHz.

Output

The MAX9680 features 5.17V/V gain. Operating from a

2.7V to 3.6V supply, the output amplifier is able to drive

a 2.3V signal into a 150I video load to ground. The out-

put is typically offset 120mV above ground to guarantee

linear operation of the amplifier. The MAX9680 output

only sources current; all loads should be connected to

ground.

Short-Circuit Protection

The MAX9680 Typical Application Circuit includes a 75I

back-termination resistor that limits short-circuit currents

for an external short applied at the video output. The

MAX9680 features internal output short-circuit protection

to prevent device damage in prototyping and applica-

tions where the amplifier output can be directly shorted.

Short-circuit protection activates if the output is short

circuited and the output current exceeds 90mA. During

short-circuit protection, the output of the MAX9680 is

shut off for 18Fs and then turns on for 0.6Fs. If the short

is still present, the MAX9680 output shuts off again.

Extended short circuits result in a pulsed output. The

device resumes normal operation after the short is

removed.

PIN

NAME

DESCRIPTION

1

IN

Input

2

GND

Ground

3

RSET

Resistor Set. The reference voltage of the current digital-to-analog converter (DAC) is applied

4

OUT

Output

5

ENABLE

Enable. Drive high to enable the device. Pull low to disable the device.

6

Positive Power Supply. Bypass to GND with a 0.1FF capacitor.