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MAX9940AXK+TMAXN/a775avaiSignal-Line Overvoltage Protector for Low-Voltage Devices


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MAX9940AXK+T
Signal-Line Overvoltage Protector for Low-Voltage Devices
General Description
The MAX9940 signal-line overvoltage protector for low-
voltage digital communication ports provides protection
against high-voltage faults and ESD strikes. The
MAX9940 is especially useful for sensitive communica-
tion protocols such as Maxim 1-Wire®that cannot
afford standard means of fault protection, such as large
series resistors or large line capacitances.
The MAX9940 operates from a single supply voltage of
+2.2V to +5.5V and consumes only 13µA of quiescent
supply current. The EXT port is protected up to 28V.
The device features a reaction time of 60ns for fast
action during fault conditions and operates over the
-40°C to +125°C automotive temperature range.
Applications

Notebook Computers
Portable Devices
Industrial Equipment
Features
28V Protection on EXTExtended ESD Protection
±4kV IEC 61000-4 Contact on EXT
+2.2V to +5.5V Supply Voltage Range13µA Quiescent Supply Current 60ns Fault Reaction TimeSmall, 5-Pin SC70-40°C to +125°C Temperature Range
MAX9940
Signal-Line Overvoltage Protector
for Low-Voltage Devices

19-4168; Rev 0; 2/09
NOTEBOOKADAPTER
MICROCONTROLLER
EXT
GND
INT
1-Wire
DEVICE
2kΩ
20V
PROTECTION
CIRCUIT
ENABLEVCC
DATA
NOTEBOOK
BATTERY
CHARGER
LOAD
VDD = 3.3V
MAX9940
Block Diagram/Typical Application Circuit
Ordering Information
PARTTEMP RANGEPIN-
PACKAGE
TOP
MARK

MAX9940AXK+-40°C to +125°C5 SC70ATC
+Denotes a lead(Pb)-free/RoHS-compliant package.
1-Wire is a registered trademark of Maxim Integrated Products, Inc.
MAX9940
Signal-Line Overvoltage Protector
for Low-Voltage Devices
ABSOLUTE MAXIMUM RATINGS

Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional
operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to
absolute maximum rating conditions for extended periods may affect device reliability.
(All voltages with respect to GND.)
VCC...........................................................................-0.3V to +6V
INT............................................................................-0.3V to +6V
EXT.........................................................................-0.3V to +30V
Continuous Input Current into Any Terminal.....................±20mA
Continuous Power Dissipation (TA= +70°C)
5-Pin SC70 (derate 3.1mW/°C above +70°C)..............245mW
Operating Temperature Range.........................-40°C to +125°C
Junction Temperature......................................................+150°C
Storage Temperature Range.............................-65°C to +150°C
PARAMETERSYMBOLCONDITIONSMINTYPMAXUNITS
POWER SUPPLY

Power-Supply VoltageVCC2.25.5V
Quiescent Supply CurrentICCVINT = 01321µA
DC CHARACTERISTICS

INT Voltage RangeVINT05.5V
EXT Voltage RangeVEXT(Note 2)-0.7+28V
EXT Rising ThresholdVTHRVCC +
VCC +
VCC +
0.30V
EXT Falling ThresholdVTHFVCC +
VCC +
VCC +
0.16V
SWITCH CHARACTERISTICS

On-ResistanceRON0 < VEXT < VCC, IEXT = ±10mA43.577.5Ω
On-CapacitanceCONCapacitance to GND38pF
INT Off-CapacitanceCOFFCapacitance to GND27pF
INT Normal Operation Leakage
Current (to GND)0 < VINT < VCC, VCC = 5.5V34.2µA
EXT Normal Operation Leakage
Current (to GND)0 < VEXT < VCC, VCC = 5.5V35µA
INT Fault Leakage CurrentVINT = 3.3V, VEXT = 28V210nA
EXT Fault Leakage CurrentVINT = 3.3V, VEXT = 28V341510µA
VCC = VDD = 0, 2.2V < VDD < 5.5V,
RINT_PULLUP = 2kΩ to VDD3870µAINT Shutdown Leakage Current
(to GND)
VCC = VDD = 01nA
AC CHARACTERISTICS

Power-Up Delay TimetPUP500µs
Fault, VEXT = 10V, RINT_PULLUP = 200Ω98200Fault Reaction TimetOFFFault, VEXT = 16V, RINT_PULLUP = 200Ω60ns
Fault Recovery TimetONFault removed, VEXT < VCC - 0.8V271375ns
Note 1:
All devices are 100% production tested at TA= +25°C. Specifications over temperature limits are guaranteed by design.
Note 2:
Minimum EXT voltage of -0.7V is allowed only with a maximum drawn current of 20mA.
ELECTRICAL CHARACTERISTICS

(VCC= +3.3V, RINT_PULLUP= 2kΩto VDD, VDD= 3.3V, TA= TMINto TMAX, unless otherwise noted. Typical values are at= +25°C.) (Note 1)
MAX9940
Signal-Line Overvoltage Protector
for Low-Voltage Devices
31456
ON-RESISTANCE
vs. VCM

MAX9940 toc01
VCM (V)
ON-RESISTANCE (VCC = 2.5V
VCC = 3.3V
VCC = 5.5V
ON-RESISTANCE
vs. VCM
MAX9940 toc02
VCM (V)
ON-RESISTANCE (
TA = +125°C
TA = +85°C
TA = +25°C
TA = -40°C
TURN-ON/TURN-OFF TIME
vs. TEMPERATURE
MAX9940 toc03
TEMPERATURE (°C)
TURN-ON/TURN-OFF TIME (ns)
TURN-ON
TURN-OFF
EXT = 0 TO 10V
SQUARE WAVE
RPULLUP = 200Ω
TURN-ON/TURN-OFF TIME
vs. TEMPERATURE
MAX9940 toc04
TEMPERATURE (°C)
TURN-ON/TURN-OFF TIME (ns)
TURN-ON
TURN-OFF
EXT = 0 TO 16V
SQUARE WAVE
RPULLUP = 200Ω
SUPPLY CURRENT
vs. SUPPLY VOLTAGE
MAX9940 toc05
SUPPLY VOLTAGE (V)
SUPPLY CURRENT (
TA = +125°C
TA = +85°C
TA = +25°C
TA = -40°C
INSERTION LOSS vs. FREQUENCY

MAX9940 toc06
FREQUENCY (Hz)
INSERTION LOSS (dB)
10M1M100k10k100M
OFF-ISOLATION
vs. FREQUENCY

MAX9940 toc07
FREQUENCY (Hz)
OFF-ISOLATION (dB)
10M1M100k10k
-120100M
INT
500mV/div
EXT
1V/div
TIME (40µs/div)
FAULT TURN-ON AND RECOVERY TIME

MAX9940 toc08
VDD = VCC = 3.3V
Typical Operating Characteristics

(VCC= +3.3V, RINT_PULLUP= 2kΩto VDD, VDD= 3.3V, TA= TMINto TMAX, unless otherwise noted.)
MAX9940
Signal-Line Overvoltage Protector
for Low-Voltage Devices
Typical Operating Characteristics (continued)

(VCC= +3.3V, RINT_PULLUP= 2kΩto VDD, VDD= 3.3V, TA= TMINto TMAX, unless otherwise noted.)
FAULT RECOVERY TIME

MAX9940 toc10
TIME (100ns/div)
INT
500mV/div
EXT
5V/div
RPULLUP = 2kΩ
FAULT TURN-ON AND RECOVERY TIME
(SCHOTTKY DIODE FROM INT TO VCC)

MAX9940 toc11
TIME (40μs/div)
INT
1V/div
EXT
5V/div
RPULLUP = 2Ω
FAULT TURN-ON TIME
(SCHOTTKY DIODE FROM INT TO VCC)

MAX9940 toc12
TIME (100ns/div)
INT
1V/div
EXT
5V/div
VTHR AND VTHF
vs. SUPPLY VOLTAGE
MAX9940 toc13
SUPPLY VOLTAGE (V)
VOLTAGE THRESHOD (mV)
VTHR
VTHF
VTHR AND VTHF
vs. TEMPERATURE
MAX9940 toc14
TEMPERATURE (°C)
VOLTAGE THRESHOLD (mV)
VTHR
VTHF
FAULT TURN-ON TIME

MAX9940 toc09
TIME (100ns/div)
INT
2V/div
EXT
5V/div
RPULLUP = 200Ω
Detailed Description
The MAX9940 is a signal-line overvoltage protector for
low-voltage devices that provides circuit protection
from high-voltage faults and ESD strikes. The device
provides protection in digital communication lines such
as 1-Wire and I2C protocols where large series resis-
tance and capacitances cannot be used to provide
protection due to their impact on VIL/VIHlevels and
communication timing. The MAX9940 includes a series
switch that connects INT to EXT. When a high-voltage
fault condition occurs on EXT, the MAX9940 quickly
shuts off the series switch and isolates the low-voltage
device from the fault condition. In addition to providing
DC fault isolation, the MAX9940 also provides up to
±4kV IEC 61000-4 contact ESD protection on EXT. The
MAX9940 is ideal for circuits that require low-voltage
devices that communicate to the outside world over
connector ports that can expose them to hazardous
high-voltage DC faults and ESD strikes.
Series Switch

The MAX9940 features a series switch to connect a
low-voltage device such as a microcontroller to an
external communication device such as a 1-Wire or I2C
slave. The internal switch is turned off when disabled or
if a fault condition exists, isolating the microcontroller
from any possible damage. The nominal switch resis-
tance is 38Ω(typ). The series switch is composed of
parallel DMOS and HV-pMOS devices as shown in the
Block Diagram/Typical Application Circuit. The series
switch cell contains circuitry that ensures the pMOS
device turns off properly when the voltage at EXT
exceeds the supply voltage. The switch can withstand
a maximum voltage of 28V at EXT.
Comparator

The MAX9940 features a low-power, high-speed com-
parator that is used to turn off the series switch if a
high-voltage condition is detected on EXT. The nominal
hysteresis of the comparator is 128mV (typical). Fault
voltages on EXT that are slightly above VCCtrigger the
comparator to quickly isolate INT and EXT channels
from each other. In this mode, the MAX9940 is able to
withstand 28V on EXT. Negative voltages on EXT are
allowed as long as they are current-limited to less than
20mA.
Typical Application Circuits

The innovative design of the MAX9940 allows it to with-
stand large DC voltages up to 28V at INT and EXT even
when VCCis 0. This allows application-specific power-
saving and fault-protection schemes to be implemented.
Figures 1 and 2 show two methods of powering the
MAX9940 from an ENABLE digital output port of the
microcontroller. Figure 3 shows the conventional method
of operating the MAX9940 with both pullup resistor for
digital communication on DATA (RP) and VCCbeing
connected directly to VDDof the microcontroller.
MAX9940
Signal-Line Overvoltage Protector
for Low-Voltage Devices
Pin Description
PINNAMEFUNCTION

1VCCPower Supply. Can be connected to a microcontroller enable input.GNDGroundN.C.No Connection. Not internally connected.INTMicrocontroller I/O Port. Connection to a microcontroller data port.EXTExternal Connector Port. Connection to a 1-Wire device.
MAX9940
In all three schemes, the MAX9940 protects the micro-
controller from both DC fault voltages above VCCand
ESD strikes on EXT. The difference in the three
schemes lies in the impact on power consumption in
battery-operated devices during normal and short to
GND fault conditions.
Figure 1 shows a recommended configuration for battery-
operated devices that need to conserve power both on
a continuous basis as well as during short to GND fault
conditions. In this scheme, the ENABLE port of a micro-
controller supplies the quiescent current for the
MAX9940 as well as that required for digital communi-
cation (i.e., RPpullup resistor). By forcing a 0 on the
ENABLE digital output port of the microcontroller, the
MAX9940 is in a zero-power shutdown mode, while also
preventing any power drain to occur in the event of a
short to GND fault on EXT. As stated earlier, EXT main-
tains the ability to withstand DC voltages up to 28V
even when VCC= 0.
In Figure 2, the ENABLE port of a microcontroller pow-
ers the MAX9940. The low 13µA operating current
allows standard digital I/O ports to easily supply the
operating current of the MAX9940 without any substan-
tial voltage drop (VOH≈VDD). By forcing a 0 on the
ENABLE port of the microcontroller, the MAX9940 can
be put into a zero-power mode, thus conserving battery
power. It should be noted that there is no internal ESD
diode from INT to VCC. This allows the voltage at INT to
stay at VDDeven though VCC= 0, thus drawing no cur-
rent from RPor the battery. However, an internal diode
does exist from INT to EXT, and therefore, in the event
of a short to GND fault on EXT, current is drawn through
RP, causing a power drain from VDD, and can potential-
ly reduce battery life.
In Figure 3, VDDpowers the MAX9940 directly, and
consumes quiescent current on a continuous basis. In
this mode, the internal FET between INT and EXT is
kept on as long as the voltage on EXT is below VCC. As
a result, in the event of a short to GND fault on EXT,
current is drawn through RP, causing a power drain
from VDDand potentially reducing battery life.
Signal-Line Overvoltage Protector
for Low-Voltage Devices

MICROCONTROLLER
EXT
GND
INT
ENABLEVCCRP
2kΩ
VDD = 3.3V
MAX9940
DATA
1-Wire
DEVICE
Figure 1. Recommended Scheme for Battery-Operated Devices that Need to Shut Down the MAX9940 and Prevent Power Draw
During Short to GND Faults
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