Outputs
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
devices have 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.
Applications Information
AC-Coupling the Outputs
The outputs can be AC-coupled since the output stage
can source and sink current as shown in Figure 3.
Coupling capacitors should be 220µF or greater to
keep the highpass filter, formed by the 150Ω equivalent
resistance of the video transmission line, to a corner
frequency of 4.8Hz or below. The frame rate of PAL
systems is 25Hz, the frame rate of NTSC systems is
30Hz, and the frame rate of VGA is usually 60Hz or
higher. The corner frequency should be well below the
frame rate.
Power Consumption
The quiescent power consumption and average power
consumption of the MAX9541/MAX9542 are very low
because of 3.3V operation and low-power circuit
design. Quiescent power consumption is defined when
the MAX9541/MAX9542 are operating without loads
and without any video signals.
Average power consumption represents the normal power
consumption when the devices drive real video signals
into real video loads. It is measured when the MAX9541/
MAX9542 drive 150Ω loads to ground with a 50% flat
field, which serves as proxy for a real video signal.
Table 4 shows the quiescent and average power con-
sumption of the MAX9541/MAX9542.
Power-Supply Bypassing and Ground
The MAX9541/MAX9542 operate from a single-supply
voltage down to 2.7V, allowing for low-power operation.
Bypass V
DD
to GND with a 0.1µF capacitor. Place all
external components as close as possible to the
device.
MAX9541/MAX9542
Quadruple, 2:1, Mux Amplifiers for
Standard-Definition and VGA Signals
______________________________________________________________________________________ 13
each input.
