MAX4028EWE+ Datasheet MAX4029EUP+T, MAX4029EUP+, MAX4029EWP+ | P7-P9

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:

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)

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

1kΩ

IN1B

CLAMP

IN2A

IN2B

OUT2

DISABLE

CLAMP/KEY_2

1kΩ

KEYREF

CLAMP

VOLTAGE

CLAMP/

KEY

CLAMP

CLAMP/

KEY

CLAMP

IN3A

IN3B

OUT3

CLAMP/KEY_3

1kΩ

CLAMP/

KEY

CLAMP

CLAMP/

KEY

CLAMP

IN4A

A/B

IN4B

GND

OUT4

CLAMP/KEY_4

1kΩ

CLAMP/

KEY

CLAMP

CLAMP/

KEY

CLAMP

Figure 1. MAX4029 Functional Diagram

MAX4028/MAX4029

Therefore, a 6kΩ resistor will produce a 1.13V key-

clamp voltage as shown in Figure 2. The clamp voltage

CLAMP

) is measured at the output; the voltage at the

input is V

CLAMP

(sync tip or key clamp) divided by the

gain (+2V/V) + V

In order for these clamps (sync tip or key) to work proper-

ly, the input must be coupled with a 0.1µF capacitor (typ)

with low leakage (<1µA to 2µA, max). Without proper cou-

pling, the clamp voltage will change during the horizontal

line time causing the “black level” to vary, changing the

image brightness from left to right on the display. In addi-

tion to the capacitor, a low resistance (≤75Ω) is required

on the source side to return the capacitor to ground. The

clamps used here are active devices with the coupling

capacitor serving two functions; first, as a charge reser-

voir to maintain the clamp voltage, and second, as the

compensation capacitor for the clamp itself. If an input is

not used, it must be terminated to avoid causing oscilla-

tions that could couple with another input.

In general, a sync-tip clamp is used for composite video

(Cvbs), gamma-corrected primaries (R’G’B’), and the

luma signal (Y) in S-video. A key clamp is preferred for

component color difference signals (Pb and Pr), linear

primaries (RGB in PCs), and chroma (C) in S-video. The

rule is to sync tip clamp a signal if sync is present and

key clamp all others. Several examples are given in the

Clamp/Key-Clamp Settings for Video Formats section.

Clamp/Key-Clamp Settings for Video Formats

Tables 1 and 2 provide the clamp settings on the

MAX4028/MAX4029 to interface with various video formats.

Low-Power, High-Impedance Disable Mode

All parts feature a low-power, high-impedance disable

mode that is activated by driving the DISABLE input

low. Placing the amplifier in disable mode reduces the

quiescent supply current and places the output imped-

ance at 2kΩ typically. Multiple devices can be paral-

leled to construct larger switch matrices by connecting

the outputs of several devices together and disabling

all but one of the paralleled amplifiers’ outputs.

Triple/Quad, 2:1 Video

Multiplexer-Amplifiers with Input Clamps

8 _______________________________________________________________________________________

KEY-CLAMP REFERENCE VOLTAGE

vs. R

KEYREF

MAX4028 fig02

KEYREF

(kΩ)

KEY-CLAMP REFERENCE VOLTAGE (V)

119753

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

113

Figure 2. Key-Clamp Reference Voltage vs. R

KEYREF

Table 1. MAX4028 Clamp Settings for Video Formats

INPUT FORMAT CLAMP/KEY

1 Cvbs1 Clamp

2 Cvbs2 Clamp

3 Cvbs3 Clamp

INPUT FORMAT CLAMP/KEY

1G’Clamp

2B’Clamp

3R’Clamp

R, G, B have sync on all.

INPUT FORMAT CLAMP/KEY

1GsClamp

2BKey

3RKey

Gs, B, R have sync only on Green.

INPUT FORMAT CLAMP/KEY

1YClamp

2CKey

3 Cvbs Clamp

INPUT FORMAT CLAMP/KEY

1YClamp

2PbKey

3PrKey

The MAX4028/MAX4029 have a fixed gain of +2V/V that

is internally set with two 1kΩ thin-film resistors. The

impedance of the internal feedback resistors must be

taken into account when operating multiple MAX4028/

MAX4029s in large multiplexer applications.

Applications Information

Video Line Driver

The MAX4028/MAX4029 are well suited to drive coaxial

transmission lines when the cable is terminated at both

ends, as shown in Figure 3, where the fixed gain of

+2V/V compensates for the loss in the resistors, R

Driving Capacitive Loads

A correctly terminated transmission line is purely resis-

tive and presents no capacitive load to the amplifier.

Reactive loads decrease phase margin and may pro-

duce excessive ringing and oscillation.

Another concern when driving capacitive loads is the

amplifier’s output impedance, which appears inductive

at high frequencies. This inductance forms an L-C reso-

nant circuit with the capacitive load, which causes

peaking in the frequency response and degrades the

amplifier’s phase margin.

MAX4028/MAX4029

Triple/Quad, 2:1 Video

Multiplexer-Amplifiers with Input Clamps

_______________________________________________________________________________________ 9

Table 2. MAX4029 Clamp Settings for Video Formats

INPUT FORMAT CLAMP/KEY

1 Cvbs1 Clamp

2 Cvbs2 Clamp

3 Cvbs3 Clamp

4 Cvbs4 Clamp

Gs, B, R have sync only on Green.

INPUT FORMAT CLAMP/KEY

1H-Sync Clamp

2GKey

3BKey

4RKey

R, G, B have sync on none.

INPUT FORMAT CLAMP/KEY

1YClamp

2CKey

3 Cvbs Clamp

4 Cvbs Clamp

R, G, B have sync on all.

75Ω

OUT_

IN_A

IN_B

A/B DISABLE

0.1µF

75Ω CABLE

75Ω

0.1µF

75Ω CABLE

KEYREF

MAX4028

MAX4029

CLAMP

Figure 3. Video Line Driver

INPUT FORMAT CLAMP/KEY

1GsClamp

2RKey

3BKey

4 Cvbs Clamp

INPUT FORMAT CLAMP/KEY

1YClamp

2PrKey

3PbKey

4 Cvbs Clamp

INPUT FORMAT CLAMP/KEY

1 Cvbs Clamp

2G’Clamp

3B’Clamp

4R’Clamp

P1-P3 P4-P6 P7-P9 P10-P12 P13-P13

MAX4028EWE+

Mfr. #:

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Manufacturer:

Maxim Integrated

Description:

Video Amplifiers Triple & Quad 2:1 Video MUX-Amplifie

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MAX4028EWE+

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