max9513atet Maxim Integrated Products, Inc., max9513atet Datasheet - Page 18

• Manufacturer Part Number: max9513atet
• Description: Max9513 Cvbs Video Filter Amplifier With Smartsleep And Bidirectional Video Support
• Manufacturer: Maxim Integrated Products, Inc.

CVBS Video Filter Amplifier with SmartSleep
and Bidirectional Video Support
The MAX9513 CVBSIN input should be directly con-
nected to the output of the video current DAC. DC-cou-
pling ensures that the input signals are ground
referenced such that the sync tip of CVBSIN is within
50mV of ground.
The EXTCVBSIN input can only handle signals with a
sync pulse, such as composite video and luma.
Because the DC level of an external video input signal
is unknown, the external video signal is AC-coupled
through a 0.1µF capacitor, and a sync tip clamp sets
the internal DC level of the MAX9513. A 2:1 multiplexer
under the control of the INT/EXT input selects either the
signal at CVBSIN or EXTCVBSIN.
The MAX9513 filter passband is 6.75MHz, which makes
the device suitable for the higher bandwidth video sig-
nals from a DVD chip. Broadcast video signals actually
require less bandwidth because of channel limitations:
NTSC signals have a 4.2MHz bandwidth, and PAL sig-
nals have a 5MHz bandwidth. Video signals from a DVD
player are not channel limited; therefore, the bandwidth
of DVD video signals can push right against 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 reduce the filtering require-
ments, most modern video systems oversample the
input by two times, thus clocking the video current DAC
at 27MHz.
The video output amplifiers can both source and sink
load current, allowing output loads to be DC- or AC-
coupled. The amplifier output stage needs approxi-
mately 300mV of headroom from either supply rail. The
MAX9513 has an internal level-shift circuit that positions
the sync tip at approximately 300mV at the output.
If the supply voltage is greater than 3.135V (5% below
a 3.3V supply), each amplifier can drive two DC-cou-
pled video loads to ground. If the supply is less than
3.135V, each amplifier can drive only one DC-coupled
or AC-coupled video load.
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Video Reconstruction Filter
Outputs
Inputs
When SHDN is low, the MAX9513 typically draws less
than 10nA supply current. All the amplifier outputs
become high impedance. The effective output resis-
tance at the video outputs is 28kΩ, due to the internal
feedback resistors to ground.
CVBSIN has a high-impedance input buffer and can
work with source resistances as high as 300Ω. To
reduce power dissipation in the video DACs, the DAC
output resistor can be scaled up in value. The reference
resistor that sets the reference current inside the video
DACs must also be similarly scaled up. For instance, if
the output resistor is 37.5Ω, the DAC must source
26.7mA when the output is 1V. If the output resistor is
increased to 300Ω, the DAC only needs to source
3.33mA when the output is 1V.
There is parasitic capacitance from the DAC output to
ground. That capacitance in parallel with the DAC out-
put resistor forms a pole that can potentially roll off the
frequency response of the video signal. For example,
300Ω in parallel with 50pF creates a pole at 10.6MHz.
To minimize this capacitance, reduce the area of the
signal trace attached to the DAC output as much as
possible, and place the MAX9513 as close to the video
DAC outputs as possible.
The outputs can be AC-coupled since the output stage
can source and sink current as shown in Figure 9.
Coupling capacitors should be 220µF or greater to keep
the highpass filter formed by the 150Ω equivalent resis-
tance of the video transmission line to a corner frequen-
cy of 4.8Hz or below. The frame rate of PAL systems is
25Hz, and the frame rate of NTSC systems is 30Hz. The
corner frequency should be well below the frame rate.
SmartSleep only works with DC-coupled loads.
The MAX9513 operates from a single-supply voltage
down to 2.7V, allowing for low-power operation. Bypass
V
components as close as possible to the device.
DD
to GND with a 0.1µF capacitor. Place all external
Power-Supply Bypassing and Ground
Applications Information
Reducing Power Consumption
AC-Coupling the Outputs
in the Video DACs
Shutdown