MAX4550/MAX4570
Serially Controlled, Dual 4x2, Clickless
Audio/Video Analog Crosspoint Switches
14 ______________________________________________________________________________________
Addressable Serial Interface
To program several MAX4570s individually using a sin-
gle processor, connect DIN of each MAX4570 together
and control CS on each MAX4570 separately. To select
a particular device, drive the corresponding CS low,
clock in the 16-bit command, then drive CS high and
execute the command. Typically, only one MAX4570 is
addressed at a time.
Improving Off-Isolation
To improve off-isolation, connect the SA or SB input to
ground either directly (DC ground) or through capaci-
tors (AC ground). Closing SA or SB effectively grounds
the unused outputs.
Using the Internal Bias Resistors
Use the internal bias-resistor networks to give the
switch outputs a DC bias when the switch terminals are
AC coupled. Programming of the switches that connect
the bias resistors to the outputs is accomplished via bit
C5 of the command byte. Connect the BIASH and
BIASL inputs to DC levels (for example, V+ and GND),
and activate the switch connecting the appropriate out-
put. This applies a voltage midway between V
BIASH
and V
BIASL
to the output (refer to Tables 1, 4, and the
Functional Diagram
).
Using the Auxiliary Outputs
The four auxiliary outputs provide a way to control
external circuitry, such as LEDs or other DC loads,
through the serial interface. Program these outputs via
bit C4 of the command byte. Each output is capable of
sourcing 1mA or sinking 12mA. They are programmed
through the command byte and data byte (refer to
Tables 1, 3, and the
Functional Diagram
).
Clickless Switching
Audible switching transients (“clicks”) are eliminated in
this mode of operation. When an output is configured
as “clickless,” the gate signal of the switches connect-
ed to that output are controlled with slow-moving volt-
ages. As a result, the output slew rates are significantly
reduced. Program clickless operation via bit C5 of the
command byte (refer to Tables 1, 4, and the
Functional
Diagram
). Each operating switch may draw as much as
2mA during transition.
Power-Up State
The MAX4550/MAX4570 feature a preset power-up
state. Upon power-up, COM1A and COM2A are con-
nected to SA, COM1B and COM2B are connected to
SB, all outputs are set to clickless mode, all bias-resis-
tor networks are disconnected from the outputs, and all
auxiliary outputs are low. All other switches are open.
Table 6. 3-Wire Serial-Interface Data Format
X = Don’t care
X
MSB
C6C7
AUXX
C4C5
BIAS COM1B
C2C3
COM1ACOM2B
C0C1
COM2A
COMMAND BYTE
D6
D6
D7 D4
D7 D4
D5
D5
D2
D2
D3
LSB
D0
D3 D0
DATA BYTE
D1
D1
