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MAX9680_10 Datasheet, PDF (6/9 Pages) Maxim Integrated Products – 3V Video Amplifier with Internal Gain and Filter in SC70
3V Video Amplifier with
Internal Gain and Filter in SC70
Pin Description
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
across the internal RSET resistor to generate the reference current of the DAC.
4
OUT
Output
5
ENABLE Enable. Drive high to enable the device. Pull low to disable the device.
6
VDD
Positive Power Supply. Bypass to GND with a 0.1FF capacitor.
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.
RSET Resistor
The video current DAC imposes a reference voltage,
VREF, across RSET. The resulting current (VREF/RSET) is
the reference current for the video current DAC.
Input
The video input should be directly connected to the out-
put of the video current DAC. RIN, the equivalent input
resistance, is 872I to ground. The output current of the
video DAC flows through RIN to create the video signal
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.
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