MAX4510/MAX4520
Rail-to-Rail, Fault-Protected,
SPST Analog Switches
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Normal Operation
Two comparators continuously compare the voltage on
the NO (or NC) pin with V+ and V-. When the signal on
NO or NC is between V+ and V-, the switch acts nor-
mally, with FETs N1 and P1 turning on and off in
response to IN signals. The parallel combination of N1
and P1 forms a low-value resistor between NO (or NC)
and COM so that signals pass equally well in either
direction.
Positive Fault Condition
When the signal on NO (or NC) exceeds V+ by about
50mV, the high-fault comparator output is high, turning
off FETs N1 and P1. This makes the NO (or NC) pin
high impedance regardless of the switch state. If the
switch state is “off,” all FETs are turned off and both NO
(or NC) and COM are high impedance. If the switch
state is “on,” FET P2 is turned on, sourcing current from
V+ to COM.
Negative Fault Condition
When the signal on NO (or NC) exceeds V- by about
50mV, the low-fault comparator output is high, turning
off FETs N1 and P1. This makes the NO (or NC) pin
high impedance regardless of the switch state. If the
switch state is “off,” all FETs are turned off and both NO
(or NC) and COM are high impedance. If the switch
state is “on,” FET N2 is turned on, sinking current from
COM to V-.
Transient Fault Response and Recovery
When a fast rise-time and fall-time transient on IN
exceeds V+ or V-, the output (COM) follows the input (IN)
to the supply rail with only a few nanoseconds delay.
This delay is due to the switch on-resistance and circuit
capacitance to ground. When the input transient returns
to within the supply rails, however, there is a longer out-
put recovery time delay. For positive faults, the recovery
time is typically 3.5µs. For negative faults, the recovery
time is typically 1.3µs. These values depend on the COM
output resistance and capacitance. The delays are not
dependent on the fault amplitude. Higher COM output
resistance and capacitance increase recovery times.
COM and IN Pins
FETs N2 and P2 can source about ±13mA from V+ or V-
to the COM pin in the fault condition. Ensure that if the
COM pin is connected to a low-resistance load, the
absolute maximum current rating of 30mA is never
exceeded, both in normal and fault conditions.
The GND, COM, and IN pins do not have fault protec-
tion. Reverse ESD-protection diodes are internally con-
nected between GND, COM, IN, and both V+ and V-. If a
signal on GND, COM, or IN exceeds V+ or V- by more
than 300mV, one of these diodes will conduct heavily.
During normal operation these reverse-biased ESD
diodes leak a few nanoamps of current to V+ and V-.
Fault-Protection Voltage and Power Off
The maximum fault voltage on the NC or NO pins is
±36V with power applied and ±40V with power off.
Failure Modes
The MAX4510/MAX4520 are not lightning arrestors or
surge protectors.
Exceeding the fault-protection voltage limits on NO or
NC, even for very short periods, can cause the device
to fail.
Ground
There is no connection between the analog signal path
and GND. The analog signal path consists of an N-
channel and P-channel MOSFET with their sources and
drains paralleled and their gates driven out of phase to
V+ and V- by the logic-level translators.
V+ and GND power the internal logic and logic-level
translators and set the input logic thresholds. The logic-
level translators convert the logic levels to switched V+
and V- signals to drive the gates of the analog switch.
This drive signal is the only connection between the
power supplies and the analog signal. GND, IN, and
COM have ESD-protection diodes to V+ and V-.
IN Logic-Level Thresholds
The logic-level thresholds are CMOS and TTL compati-
ble when V+ is +15V. As V+ is raised, the threshold
increases slightly, and when V+ reaches 25V, the level
threshold is about 2.8V—above the TTL output high-
level minimum of 2.4V, but still compatible with CMOS
outputs (see Typical Operating Characteristics).
Increasing V- has no effect on the logic-level thresholds,
but it does increase the gate-drive voltage to the signal
FETs, reducing their on-resistance.
Dual Supplies
The MAX4510/MAX4520 operate with dual supplies
between ±4.5V and ±20V. The V+ and V- supplies
need not be symmetrical, but their difference cannot
exceed the absolute maximum rating of 44V.
Single Supply
The MAX4510/MAX4520 operate from a single supply
between +9V and +36V when V- is connected to GND.
