Rainbow Electronics MAX4029 - Manual (Page 7)

Detailed Description
The MAX4028/MAX4029 are 5V, triple/quad, 2:1 voltage-
feedback multiplexer-amplifiers with input clamps and a
fixed gain of +2V/V (6dB). Channel 1 (IN1A and IN1B)
inputs are clamped to the video sync tip of the input
IN1_ channel, while the remaining inputs can be
clamped to either the video sync tip of the respective
input channel (IN_A and IN_B) or the video sync of
channel 1 (IN1_). The latter is referred to as a key
clamp and is pin selectable. Selectable clamp/key-
clamp inputs and fixed-gain video output buffers make
the MAX4028/MAX4029 ideal for video-source switching
applications such as automotive entertainment systems,
video projectors, and displays/TVs. Both devices have
20ns channel switching times and low ±10mV
P-P
switch-
ing transients, making them ideal for both high-speed
video switching applications such as OSD insertion.
The MAX4028/MAX4029 have a -3dB large-signal (2V
P-P
)
bandwidth of 130MHz, a -3dB small-signal bandwidth of
210MHz, and a 300V/µs slew rate. Low differential gain
and phase errors of 0.2% and 0.4°, respectively, make
these devices ideal for broadcast video applications.
Sync Tip and Key Clamps
The MAX4028/MAX4029 have AC-coupled inputs, with
either a sync tip or key clamp to provide bias for the
video signal. Channel 1 of the MAX4028/MAX4029
always has a sync tip clamp at the input, while the
remaining channels are selectable as either sync tip or
key clamps to accommodate the various video wave-
forms (see the Clamp/Key-Clamp Settings for Video
Formats section). The value of the sync-tip clamp voltage
is set internally for the lowest value, consistent with linear
operation, and cannot be adjusted. The key-clamp volt-
age is adjustable, to compensate for variations in the
voltage between component video inputs such as Linear
RGB, YPbPr, and Y-C, by varying R
KEYREF
. The key-
clamp voltage can be computed from:
V Key-Clamp = 0.40 + 2000/[(5000 x R KEYREF ) /
(5000 + R
KEYREF
)]
MAX4028/MAX4029
Triple/Quad, 2:1 Video
Multiplexer-Amplifiers with Input Clamps
_______________________________________________________________________________________ 7
Pin Description (continued)
PIN
MAX4028 MAX4029
NAME FUNCTION
15 18 OUT1 Amplifier Output 1
16 19 DISABLE
Disable Input. Pull DISABLE high for normal operation. Drive DISABLE low to disable
all outputs.
— 20 CLAMP/KEY_4
Output 4 Clamp or Key-Clamp Input. Drive CLAMP/KEY_4 high to clamp OUT4.
Drive CLAMP/KEY_4 low to key clamp OUT4.
MAX4029
IN1A
OUT1
CLAMP
V CC
1k Ω
1k Ω
IN1B
CLAMP
IN2A
IN2B
OUT2
DISABLE
CLAMP/KEY_2
1k Ω
1k Ω
KEYREF
CLAMP
VOLTAGE
CLAMP/
KEY
CLAMP
CLAMP/
KEY
CLAMP
IN3A
IN3B
OUT3
CLAMP/KEY_3
1k Ω
1k Ω
CLAMP/
KEY
CLAMP
CLAMP/
KEY
CLAMP
IN4A
A/B
IN4B
GND
OUT4
CLAMP/KEY_4
1k Ω
1k Ω
CLAMP/
KEY
CLAMP
CLAMP/
KEY
CLAMP
Figure 1. MAX4029 Functional Diagram