MAX9655AEE+ Datasheet MAX9655AEE+, MAX9655AEE+T, MAX9656EVKIT+ | P7-P9

MAX9655/MAX9656

Low-Power Video Switches

for Dual SCART Connectors

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Detailed Description

A MAX9655 or a MAX9656 can comprise the video por-

tion of a low-cost, dual SCART solution in set-top boxes

with a subset of the full SCART functions. The

MAX9655/MAX9656 select whether the CVBS, red,

green, and blue video signals from the encoder or the

VCR SCART are routed to the TV SCART. The

MAX9655/MAX9656 support the output of one CVBS

signal to the VCR SCART. In the MAX9655, the CVBS

signal from the encoder is routed to the VCR SCART.

In the MAX9656, the CVBS signal routed to the VCR

SCART can come from the encoder or TV SCART. In

the typical usage case, the VCR (or DVD recorder)

records a television program from the set-top box. In

such a case, the encoder would be the source of the

CVBS signal. Support for the TV SCART CVBS return

path is useful when a person wants to record on his

VCR (or more likely DVD recorder) a television program

received through the television’s antenna. The televi-

sion program is transmitted from the television to the

set-top box and then to the VCR.

Both the MAX9655 and MAX9656 have integrated

reconstruction filters so that when the encoder video

signals are routed to the TV SCART or the VCR SCART,

the steps and spikes left by the video digital-to-analog

converter (DAC) are smoothed away. Although the

incoming video signals from the VCR SCART are

assumed to be filtered already, the reconstruction filter

has wide enough bandwidth so that the video signals

from the VCR SCART are not degraded.

Pin Description

MAX9655 MAX9656

NAME FUNCTION

1 2 ENC_B_IN Encoder Blue Video Input. AC-couple the signal through a 0.1µF capacitor.

2 3 ENC_G_IN Encoder Green Video Input. AC-couple the signal through a 0.1µF capacitor.

3 4 ENC_R_IN Encoder Red Video Input. AC-couple the signal through a 0.1µF capacitor.

4 5 ENC_CVBS_IN Encoder Composite Video Input. AC-couple the signal through a 0.1µF capacitor.

5 6 VCR_B_IN VCR SCART Blue Video Input. AC-couple the signal through a 0.1µF capacitor.

6 7 VCR_G_IN VCR SCART Green Video Input. AC-couple the signal through a 0.1µF capacitor.

7 8 VCR_R_IN VCR SCART Red Video Input. AC-couple the signal through a 0.1µF capacitor.

8 9 VCR_CVBS_IN V C R S C ART C om p osi te V i d eo Inp ut. AC - coup l e the si g nal thr oug h a 0.1µF cap aci tor .

9 11 GND Ground

10 13 VCR_CVBS_OUT VCR SCART Composite Video Output. The sync tip is biased at 0.3V.

11 14 TV_CVBS_OUT TV SCART Composite Video Output. The sync tip is biased at 0.3V.

12 15 TV_R_OUT TV SCART Red Video Output. The sync tip is biased at 0.3V.

13 16 TV_G_OUT TV SCART Green Video Output. The sync tip is biased at 0.3V.

14 17 TV_B_OUT TV SCART Blue Video Output. The sync tip is biased at 0.3V.

15 18 TV_SEL

TV SCART Output Selection. Connect to GND to route the encoder video signals

to the TV SCART outputs. Connect to V

to route the VCR SCART video signals

to the TV SCART outputs.

16 19 V

Positive Power Supply. Bypass with 0.1µF ceramic capacitors to GND.

— 1 TV_CVBS_IN

Television SCART Composite Video Input. AC-couple the signal through a 0.1µF

capacitor.

— 10 N.C. No Connection. Not internally connected.

—12 SHDN

Active-Low Shutdown Logic Input. Connect to GND to place device in shutdown.

Connect to V

for normal operation.

— 20 VCR_SEL

VCR SCART Output Selection. Connect to GND to route ENC_CVBS_IN to the

VCR SCART CVBS output. Connect to V

to route TV_CVBS_IN to the VCR

SCART CVBS output.

MAX9655/MAX9656

Low-Power Video Switches

for Dual SCART Connectors

8 _______________________________________________________________________________________

The incoming video signals can have any DC bias

because the input sync-tip clamps restore the

DC level. The output amplifiers have a gain of 2V/V.

The MAX9655/MAX9656 operate from a single 3.3V

supply and consume low quiescent power and low

average power. In addition, the MAX9656 also has

shutdown mode.

Operating Modes

TV_SEL controls whether the encoder or VCR video sig-

nals are sent to the TV SCART. See Table 1.

On the MAX9656, VCR_SEL controls whether the CVBS

signal from the TV SCART or the encoder is sent to the

VCR SCART. SHDN controls whether the device is on

or off. See Tables 2 and 3. In shutdown, the outputs of

the MAX9656 are high impedance.

Input

Every video signal must be AC-coupled to the

MAX9655/MAX9656 through 0.1µF capacitors. The

MAX9655/MAX9656 have sync-tip clamps and bias cir-

cuits to restore the DC level of the video signal after the

input coupling capacitor. When a video input is select-

ed, the input has a sync-tip clamp, which accepts

video signals that have sync pulses or that reach their

minimum level during sync. Composite video with

blanking and sync (CVBS) is an example of a video sig-

nal with sync pulses. The red, green, and blue signals

in an RGBS signal set are examples of signals that

return to their blank level during sync. The sync-tip volt-

age is internally set to 300mV.

When a video input is not selected, the inputs to the

MAX9655 and the MAX9656 do not distort the video

signal in case the video source is driving video signals

to another video circuit such as a video multiplexer.

The inputs are biased at V

/3, which is sufficiently

above ground so that the ESD diodes never forward

bias as the video signal changes. The input resistance

is 220kΩ, which presents negligible loading on the

video current DAC. The sole exception to this condition

is ENC_CVBS_IN (MAX9655), in which the input circuit

is always a sync-tip clamp. Table 4 summarizes which

input circuit is active on the inputs of the MAX9655

depending on TV_SEL. Table 5 summarizes which input

circuit is active on the inputs of the MAX9656 depend-

ing on TV_SEL and VCR_SEL.

LOGIC STATE MODE

Low

Encoder video signals are routed to the

TV SCART.

High

VCR SCART video signals are routed to

the TV SCART.

Table 1. TV_SEL Logic (Applicable to

Both the MAX9655 and the MAX9656)

LOGIC STATE MODE

Low

CVBS signal from encoder is routed to the

VCR SCART.

High

CVBS signal from the TV SCART is routed

to the VCR SCART.

Table 2. VCR_SEL Logic (Only Applicable

to the MAX9656)

LOGIC STATE MODE

Low Off

High On

Table 3. SHDN Logic (Only Applicable to

the MAX9656)

INPUT

INPUT CIRCUIT

(TV_SEL = LOW)

INPUT CIRCUIT

(TV_SEL = HIGH)

ENC_B_IN Sync-tip clamp Bias

ENC_G_IN Sync-tip clamp Bias

ENC_R_IN Sync-tip clamp Bias

ENC_CVBS_IN Sync-tip clamp Sync-tip clamp

VCR_B_IN Bias Sync-tip clamp

VCR_G_IN Bias Sync-tip clamp

VCR_R_IN Bias Sync-tip clamp

VCR_CVBS_IN Bias Sync-tip clamp

Table 4. MAX9655 Input Circuit of Input as Determined by State of TV_SEL

MAX9655/MAX9656

Low-Power Video Switches

for Dual SCART Connectors

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When the MAX9656 is in shutdown, its inputs are

biased at the same voltage and present the same input

resistance as unselected inputs.

Video Filter

The MAX9655/MAX9656 video filter features ±1dB

passband out to 9.5MHz and 47dB attenuation at

27MHz, making the filter suitable for standard-definition

video signals from all sources (e.g., broadcast and

DVD). Broadcast video signals are channel limited:

NTSC signals have 4.2MHz bandwidth, and PAL sig-

nals have 5MHz bandwidth. Video signals from a DVD

player, however, are not channel limited; so the band-

width of DVD video signals can approach 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 ease the filtering require-

ments, most modern video systems oversample by two

times, clocking the video current DAC at 27MHz.

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

Audio Switch for Dual SCART Connectors

In addition to video signals, SCART connectors also

support left and right audio signals that are full duplex.

Figure 1 shows a matching audio switch for the

MAX9655. Notice that it can be made from low-cost,

discrete components. It is assumed that the set-top box

chip generates the left and right audio signals directly,

or the set-top box chip sends an I

S stream to a stereo

audio DAC that generates the left and right audio sig-

nals. In both cases, the audio signals are filtered and

amplified by a dual audio op amp before they are pre-

sented to the audio switch.

Figure 2 shows a matching audio switch for the

MAX9656. Similar to how the MAX9656 handles video

signals, the audio signals from the set-top box chip or

the audio signals from the TV SCART are routed to the

VCR SCART.

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 corner frequency should be well

below the frame rate.

INPUT

INPUT CIRCUIT

(TV_SEL = LOW)

INPUT CIRCUIT

(TV_SEL = HIGH)

ENC_B_IN Sync-tip clamp Bias

ENC_G_IN Sync-tip clamp Bias

ENC_R_IN Sync-tip clamp Bias

ENC_CVBS_IN

Sync-tip clamp

(VCR_SEL = 0)

Sync-tip clamp (VCR_SEL = 1) Sync-tip clamp (VCR_SEL = 0)

Bias

(VCR_SEL = 1)

TV_CVBS_IN

Bias

(VCR_SEL = 0)

Sync-tip clamp

(VCR_SEL = 1)

Bias

(VCR_SEL = 0)

Sync-tip clamp

(VCR_SEL = 1)

VCR_B_IN Bias Sync-tip clamp

VCR_G_IN Bias Sync-tip clamp

VCR_R_IN Bias Sync-tip clamp

VCR_CVBS_IN Bias Sync-tip clamp

Table 5. MAX9656 Input Circuit of Input as Determined by State of TV_SEL

Note: VCR_SEL = X (don’t care), except where noted.

P1-P3 P4-P6 P7-P9 P10-P12 P13-P15 P16-P17

MAX9655AEE+

Mfr. #:

Buy MAX9655AEE+

Manufacturer:

Maxim Integrated

Description:

Video Switch ICs Video Switch f/Dual SCART Connector

Lifecycle:

New from this manufacturer.

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MAX9655AEE+

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