Rainbow Electronics MAX9671 - Manual (Page 13)

MAX9670/MAX9671
Low-Power Audio/Video Switch with Audio
Volume Control for Dual SCART Connectors
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Detailed Description
The MAX9670/MAX9671 represents Maxim’s third gen-
eration of SCART audio/video (A/V) switches. Under I
2 C
control, these devices route audio, video, and control
information between the set-top box decoder chip and
two SCART connectors. The audio signals are left audio
and right audio. The video signals are composite video
with blanking and sync (CVBS) and component video
(red, green, blue). S-video (Y/C) can be transported
across the SCART interface if CVBS is reassigned to
luma (Y) and red is reassigned to chroma (C). Support
for S-video is optional. The slow-switch signal and the
fast-switch signal carry control information. The slow-
switch signal is a 12V, three-level signal that indicates
whether the picture aspect ratio is 4:3 or 16:9 or causes
the television to use an internal A/V source such as an
antenna. The fast-switch signal indicates whether the
television should display CVBS or RGB signals.
CVBS, left audio, and right audio are full duplex. All the
other signals are half duplex. Therefore, one device on
the link must be designated as the transmitter, and the
other device must be designated as the receiver.
The low power consumption and the advanced monitor-
ing functions of the MAX9670/MAX9671 enable the cre-
ation of lower power set-top boxes, televisions, and
DVD players. Unlike competing SCART ICs, the audio
and video circuits of the MAX9670/MAX9671 operate
entirely from 3.3V rather than from 5V and 12V. Only the
slow-switch circuit of the MAX9670/MAX9671 requires a
12V supply. The MAX9670/MAX9671 also have circuits
that detect activity on the CVBS inputs, loads on the
CVBS outputs, and the level of the slow-switch signals.
The INT signal informs the microcontroller if there are
any changes so that the microcontroller can intelli-
gently decide whether to power up or power down
the equipment.
In addition, the MAX9670/MAX9671 have DirectDrive
audio circuitry to eliminate click-and-pop noise. With
DirectDrive, the DC bias of the audio line outputs is
always at ground, no matter whether the MAX9670/
MAX9671 are being powered up or powered down.
Conventional audio line output drivers that operate from a
single supply require series AC-coupling capacitors.
During power-up, the DC bias on the AC-coupling capac-
itor moves from ground to a positive voltage, and during
power-down, the opposite occurs. The changing DC bias
usually causes an audible transient.
Pin Description (continued)
PIN
MAX9670 MAX9671
NAME FUNCTION
28 31 GNDVID Video Ground
29 32 VCR_R/C_IN VCR SCART Red/Chroma Video Input
30 33 V VID
Video and Digital Supply. Connect to a 3.3V supply. Bypass with parallel 1µF and
0.1µF ceramic capacitors to GNDVID. V
VID also serves as a digital supply for the
I 2 C interface.
31 34 ENC_C_IN Encoder Chroma Video Input
32 35 ENC_R/C_IN Encoder Red/Chroma Video Input
33 36 TV_R/C_OUT TV SCART Red/Chroma Video Output
34 37 VCR_R/C_OUT VCR SCART Red/Chroma Video Output
35 38 VCR_Y/CVBS_OUT VCR SCART Luma/Composite Video Output
36 39 TV_Y/CVBS_OUT TV SCART Luma/Composite Video Output
37 40 VCR_Y/CVBS_IN VCR SCART Luma/Composite Video Input
38 41 TV_Y/CVBS_IN TV SCART Luma/Composite Video Input
39 42 ENC_Y_IN Encoder Luma Video Input
40 43 ENC_Y/CVBS_IN Encoder SCART Luma/Composite Video Input
— — EP
Exposed Pad. The exposed pad is the internal ground for the audio amplifiers and
charge pump. A low-impedance connection between ground and EP is required
for proper isolation.