MAX9671CTH+T Maxim Integrated Products, MAX9671CTH+T Datasheet - Page 15

• Manufacturer Part Number: MAX9671CTH+T
• Description: IC AUDIO/VIDEO SWIT DUAL 44TQFN
• Manufacturer: Maxim Integrated Products

Specifications of MAX9671CTH+T

• Function: Audio/Video Switch
• Circuit: 2 x SCART
• Voltage Supply Source: Single Supply
• Voltage - Supply, Single/dual (±): 3.3 V ~ 12 V
• Operating Temperature: 0°C ~ 70°C
• Mounting Type: Surface Mount
• Package / Case: 44-TQFN Exposed Pad
• For Use With: MAX9671EVKIT+ - EVALUATION KIT FOR MAX9671
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

The TV audio channel incorporates a zero-crossing
detect (ZCD) circuit that minimizes click noise due to
abrupt signal level changes that occur when switching
between audio signals at an arbitrary moment.
To implement the zero-crossing function when switch-
ing audio signals, set the ZCD bit high (Audio Control
register 00h, bit 6). Then set the mute bit high (Audio
Control register 00h, bit 0). Next, wait for a sufficient
period of time for the audio signal to cross zero. This
period is a function of the audio signal path’s low-fre-
quency 3dB corner (f
time period to wait for a zero-crossing detect is 1/20Hz
or 50ms.
After the wait period, select a new audio source for the
TV audio channel by writing to bits 1 and 0 of TV Audio
Control register (01h). Finally, clear mute (Audio Control
register, 00h, bit 0), but leave ZCD (Audio Control reg-
ister 00h, bit 6) high. The MAX9670/MAX9671 switches
the signal out of mute at the next zero crossing. See
Tables 12 and 13.
Figure 2. Conventional Driver Output Waveform vs. MAX9670/
MAX9671 Output Waveform.
Volume Control for Dual SCART Connectors
V
+V
-V
DD
GND
GND
V
Low-Power Audio/Video Switch with Audio
DD
DD
DD
/2
CONVENTIONAL DRIVER-BIASING SCHEME
______________________________________________________________________________________
L3dB
DirectDrive BIASING SCHEME
). Thus, if f
V
OUT
Clickless Switching
L3dB
= 20Hz, the
V
2V
DD
DD
The MAX9670/MAX9671 audio output amplifiers feature
Maxim’s DirectDrive architecture, thereby eliminating
the need for output-coupling capacitors required by
conventional single-supply audio line drivers. An inter-
nal charge pump inverts the positive supply (V
creating a negative supply (CPVSS). The audio output
amplifiers operate from these bipolar supplies with their
outputs biased about audio ground (Figure 2). The ben-
efit of this audio ground bias is that the amplifier out-
puts do not have a DC component. The DC-blocking
capacitors required with conventional audio line drivers
are unnecessary, conserving board space, reducing
system cost, and improving frequency response.
Conventional single-supply audio line drivers have their
outputs biased about a nominal DC voltage (typically
half the supply) for maximum dynamic range. Large
coupling capacitors are needed to block this DC bias.
Clicks and pops are created when the coupling capaci-
tors are charged during power-up and discharged dur-
ing power-down.
The MAX9670/MAX9671 features a low-noise charge
pump that requires only two small ceramic capacitors.
The 580kHz switching frequency is well beyond the
audio range and does not interfere with audio signals.
The switch drivers feature a controlled switching speed
that minimizes noise generated by turn-on and turn-off
transients.
The SCART standard specifies 2V
for audio signals. As the audio circuits process
0.5V
MAX9670/MAX9671, the gain-of-4 output amplifiers
restore the audio signals to a full-scale of 2V
To select which audio input source is routed to the TV
SCART connector, write to bits 1 and 0 of the TV Audio
Control register (01h). To select which audio input
source is routed to the VCR SCART connector, write to
bits 3 and 2 of the TV Audio Control register (01h). The
power-on default is for the TV and VCR audio outputs to
be muted (the inputs of the output amplifiers are con-
nected to audio ground). See Tables 10 and 13.
Volume control is programmable from -62dB to 0dB in
2dB steps through I
a resistive ladder network to generate 31 2dB volume
control steps, a unity gain buffer to isolate the input
from the resistive ladder, switches (MPLx and MNLx)
that select 1 of 32 nodes on the resistive ladder, and
logic to decode the the I
Table 12.
RMS
full-scale audio signals internal to the
2
C interface. The block consists of
2
C volume control value. See
RMS
Volume Control
as the full-scale
Audio Outputs
RMS
.
AUD
15
),