MAX14778 Datasheet, PDF (10/15 Pages) Maxim Integrated Products – Dual 25V Above- and Below-the-Rails 4:1 Analog Multiplexer

MAX14778
Dual ±25V Above- and Below-the-Rails
4:1 Analog Multiplexer
Truth Tables
Table 1. MUX A Channel Selection
ENA
SA1
SA0
0
X
X
1
0
0
1
0
1
1
1
0
1
1
1
ACOM
CONNECTED TO
Open
A0
A1
A2
A3
X = Don’t care
Table 2. MUX B Channel Selection
ENB
SB1
SB0
0
X
X
1
0
0
1
0
1
1
1
0
1
1
1
X = Don’t care
BCOM
CONNECTED TO
Open
B0
B1
B2
B3
Detailed Description
The MAX14778 dual 4:1 analog multiplexer integrates
bias circuitry to provide a Q25V analog voltage range
with a single 3.0 to 5.5V supply. This extended input
range allows multiplexing different communications
signals such as RS-232, RS-485, audio and USB 1.1 onto
the same connector.
Integrated Bias Generation
The MAX14778 contains a total of three charge pumps to
generate bias voltages for the internal switches: a 5V regu-
lated charge pump, a positive high-voltage (+35V) charge
pump, and a negative high-voltage (-27V) charge pump.
When V_DD is above 4.7V (typ), the 5V regulated charge
pump is bypassed and V_DD provides the input for the high-
voltage charge pumps, reducing overall supply current.
An external 1.0FF capacitor is required for each
high-voltage charge pump between V_P/V_N and GND.
Analog Signal Levels
The MAX14778 transmits signals of up to Q25V with a
single 3.0 to 5.5V supply due to integrated bias circuitry.
The device features 1.5Ω (max) on-resistance and 3mI
(typ) flatness for analog signals between -25V and +25V
(see the Typical Operating Characteristics). The current
flow through the multiplexers can be bidirectional, allow-
ing operation either as a multiplexer or demultiplexer.
Digital Interface
The MAX14778 has two digital select inputs for each
MUX: SA1 and SA0 control MUX A; SB1 and SB0 control
MUX B. Drive the digital select inputs high or low to select
which input (A_, B_) is connected to the common termi-
nal (ACOM, BCOM) for each MUX. See the Truth Tables
for more information.
Each MUX features an independent enable input (ENA
and ENB). Drive ENA or ENB low to disconnect all inputs
from the common terminal for that MUX, regardless of the
status of the select inputs or the other enable input.
Applications Information
Connector Sharing
The MAX14778 supports a Q25V analog signal range
independently for each input/output, allowing physical
connector sharing between interface types that have
differing signal ranges.
The multiprotocol connector-sharing application in the
Typical Operating Circuits shows an application with
RS-232, half-duplex RS-485, full-speed USB 1.1, and
audio signals sharing the same connector. The device
allows signals to pass over the entire signal range speci-
fied by each standard while safely isolating the unused
transceivers.
Power-Up Conditions
Ensure that no negative signals are present on the A_,
B_, or ACOM/BCOM inputs before one second has
passed after applying V_DD.
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