MAX9598 Maxim Integrated Products, MAX9598 Datasheet - Page 23

• Manufacturer Part Number: MAX9598
• Description: Low-Power Audio/Video Switch
• Manufacturer: Maxim Integrated Products

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The MAX9598 supports S-video from the set-top box to
the TV, set-top box to the VCR, and VCR to the set-top
box. S-video was not included in the original SCART
specifications but was added afterwards. As a conse-
quence, the luma (Y) signal of S-video shares the same
SCART pin as the CVBS signal. Likewise, the chroma
(C) signal shares the same SCART pin as the red sig-
nal. The pins that can carry both CVBS and luma have
Y/CVBS in their names, and the pins that can carry red
and chroma have R/C in their names.
Now, the Y/CVBS signals are full duplex while the R/C
signals are half duplex. Therefore, S-video is limited to
being half duplex. The MAX9598 has to transmit a chro-
ma signal and receive a chroma signal on the same
SCART pin, but not at the same time. The 75Ω resistor
connected to VCR_R/C_OUT must act as a back termi-
nation resistor when the MAX9598 is transmitting chro-
ma signal and as an input termination resistor when it is
receiving a chroma signal. Figure 14 shows how the
Figure 14. Gain-of-2 Amplifier on VCR_R/C_OUT Outputs Chroma Signal to VCR SCART Connector (Note the Pulldown Switch on
VCR_R/C_OUT Is Open)
0.1μF
VCR_R/C_IN
ENC_R/C_IN
ENC_C_IN
______________________________________________________________________________________
BIAS
BIAS
BIAS
MAX9598
Low-Power Audio/Video Switch for
LPF
LPF
S-Video
Dual SCART Connectors
MAX9598 transmits a chroma signal to the VCR SCART
connector while Figure 15 shows how the MAX9598
receives a chroma from the VCR SCART connector.
Write a 0 into bit 2 of register 09h to open the pulldown
switch at VCR_R/C_OUT. To close the pulldown switch,
write a 0 into bit 6 of register 0Dh to turn off the output
amplifier, and then write a 1 into bit 2, register 09h. See
Tables 15 and 16.
If the set-top box modulates CVBS and mono audio onto
an RF carrier (for example, channel 3), then a simple
application circuit can provide the needed signals (see
Figure 16). A 10kΩ resistor summer circuit between
TV_OUTR and TV_OUTL creates the mono audio signal.
The resistor-divider to ground on TV_Y/CVBS_OUT cre-
ates a video signal with normal amplitude. The unique
feature of the MAX9598 that facilitates this application
circuit is that the audio and video output amplifiers of
the MAX9598 can drive multiple loads if VAUD and VVID
are both greater than 3.135V.
A
A
V
V
= 2V/V
= 2V/V
ON
Interfacing to an RF Modulator
TV_R/C_OUT
VCR_R/C_OUT
75Ω
75Ω
SCART
SCART
VCR
TV
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