MAX498 Datasheet, PDF (10/16 Pages) Maxim Integrated Products – Quad/Triple, SPDT, RGB Switches with 250MHz Video Buffer Amplifiers

Quad/Triple, SPDT, RGB Switches
with 250MHz Video Buffer Amplifiers
______________ Detailed Description
The MAX498/MAX499 are quad/triple video switches
with high-speed, closed-loop, voltage-feedback ampli-
fiers set to a 2V/V gain. Figure 1 shows typical applica-
tion circuits. The amplifiers use a unique two-stage,
voltage-feedback architecture that combines the bene-
fits of conventional voltage-feedback and current-
feedback topologies to achieve wide bandwidths and
high slew rates while maintaining precision.
Figure 2 is a simplified block diagram of the MAX498/
MAX499. All four amplifier/switch blocks are identical to
that shown for Ch_0. A common control logic block
accepts external logic inputs A0, EN, CS, and LE,
and controls the status of switches S1, S2, and S3 of
each amplifier in parallel, as described in the Digital
Interface section.
S3 is open in the enabled state, and if Ch_A is select-
ed, S1 is connected to IN_A and S2 is connected to
GND. If Ch_B is selected, S1 is connected to GND and
S2 is connected to IN_B. Connecting the deselected
GM_ block to GND ensures minimum feedthrough.
S3 is closed in the disabled state, and both S1 and S2
are connected to GND. Disconnecting both inputs and
connecting the amplifier’s inputs to GND significantly
improves off-isolation.
__________Applications Information
Power Dissipation
The MAX498/MAX499’s maximum output current is limit-
ed by the package’s maximum allowable power dissi-
pation. The maximum junction temperature should not
exceed +150°C. Power dissipation increases with load,
and this increase can be approximated by one of the
following equations:
| | For VOUT > 0V: VCC - VOUT ILOAD
OR
| | For VOUT < 0V: VEE - VOUT ILOAD.
These devices can drive 100Ω loads connected to
each of the outputs over the entire rated output swing
and temperature range. While the output is short-circuit
protected to 120mA, this does not necessarily guaran-
tee that under all conditions, the maximum junction
temperature will not be exceeded. Do not exceed the
derating values given in the Absolute Maximum Ratings
section.
IN0A
S1
IN0B
S2
GM_A
CC
R₀
MAX498
MAX499
CHANNEL 0
X1
OUT0
GM_B
X1
S3
RFB
RG
CHANNEL 1
CHANNEL 2
CHANNEL 3
S1
S2
S3
A0
EN
CS
CONTROL LOGIC
LE
Figure 2. Block Diagram
Total Noise
The MAX498/MAX499’s low 2.6pA/√Hz input current
noise and 7.8nV/√Hz voltage noise provide for lower
total noise compared to typical current-mode feedback
amplifiers, which usually have significantly higher input
current noise. The input current noise multiplied by the
feedback resistor is the dominant noise source of cur-
rent-mode feedback amplifiers.
Differential Gain and Phase Errors
Differential gain and phase errors are critical specifica-
tions for a buffer in composite (NTSC, PAL, SECAM) video
applications, because these errors correspond directly to
color changes in the displayed picture of composite video
systems. The MAX498/MAX499’s low differential gain and
phase errors (0.03%/0.06°) make them ideal in broadcast-
quality, composite video applications.
10 ______________________________________________________________________________________