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19-4168; Rev 0; 2/09
Signal-Line Overvoltage Protector for Low-Voltage Devices
General Description
The MAX9940 signal-line overvoltage protector for lowvoltage digital communication ports provides protection against high-voltage faults and ESD strikes. The MAX9940 is especially useful for sensitive communication protocols such as Maxim 1-Wire (R) 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 13A 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 -40C to +125C automotive temperature range. 28V Protection on EXT Extended ESD Protection 4kV IEC 61000-4 Contact on EXT +2.2V to +5.5V Supply Voltage Range 13A Quiescent Supply Current 60ns Fault Reaction Time Small, 5-Pin SC70 -40C to +125C Temperature Range
Features
MAX9940
Applications
Notebook Computers Portable Devices Industrial Equipment
PART MAX9940AXK+
Ordering Information
TEMP RANGE -40C to +125C PINPACKAGE 5 SC70 TOP MARK ATC
+Denotes a lead(Pb)-free/RoHS-compliant package.
1-Wire is a registered trademark of Maxim Integrated Products, Inc.
Block Diagram/Typical Application Circuit
NOTEBOOK VDD = 3.3V ADAPTER
LOAD
NOTEBOOK BATTERY CHARGER
ENABLE
VCC
MAX9940 MICROCONTROLLER 2k + PROTECTION CIRCUIT EXT INT Tx N P
DATA Rx
1-Wire DEVICE Rx
20V
Tx
GND
________________________________________________________________ Maxim Integrated Products
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Signal-Line Overvoltage Protector for Low-Voltage Devices MAX9940
ABSOLUTE MAXIMUM RATINGS
(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 = +70C) 5-Pin SC70 (derate 3.1mW/C above +70C) ..............245mW Operating Temperature Range .........................-40C to +125C Junction Temperature ......................................................+150C Storage Temperature Range .............................-65C to +150C
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.
ELECTRICAL CHARACTERISTICS
(V CC = +3.3V, R INT_PULLUP = 2k to V DD, V DD = 3.3V, T A = T MIN to T MAX, unless otherwise noted. Typical values are at TA = +25C.) (Note 1)
PARAMETER POWER SUPPLY Power-Supply Voltage Quiescent Supply Current DC CHARACTERISTICS INT Voltage Range EXT Voltage Range EXT Rising Threshold EXT Falling Threshold SWITCH CHARACTERISTICS On-Resistance On-Capacitance INT Off-Capacitance INT Normal Operation Leakage Current (to GND) EXT Normal Operation Leakage Current (to GND) INT Fault Leakage Current EXT Fault Leakage Current INT Shutdown Leakage Current (to GND) AC CHARACTERISTICS Power-Up Delay Time Fault Reaction Time Fault Recovery Time tPUP tOFF tON Fault, VEXT = 10V, RINT_PULLUP = 200 Fault, VEXT = 16V, RINT_PULLUP = 200 Fault removed, VEXT < VCC - 0.8V 500 98 60 271 375 200 s ns ns RON CON COFF 0 < VEXT < VCC, IEXT = 10mA Capacitance to GND Capacitance to GND 0 < VINT < VCC, VCC = 5.5V 0 < VEXT < VCC, VCC = 5.5V VINT = 3.3V, VEXT = 28V VINT = 3.3V, VEXT = 28V VCC = VDD = 0, 2.2V < VDD < 5.5V, RINT_PULLUP = 2k to VDD VCC = VDD = 0 43.5 38 27 3 3 2 341 38 1 4.2 5 10 510 70 77.5 pF pF A A nA A A nA VINT VEXT VTHR VTHF (Note 2) 0 -0.7 VCC + 0.19 VCC + 0.09 VCC + 0.26 VCC + 0.13 5.5 +28 VCC + 0.30 VCC + 0.16 V V V V VCC ICC VINT = 0 2.2 13 5.5 21 V A SYMBOL CONDITIONS MIN TYP MAX UNITS
Note 1: All devices are 100% production tested at TA = +25C. 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.
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Signal-Line Overvoltage Protector for Low-Voltage Devices
Typical Operating Characteristics
(VCC = +3.3V, RINT_PULLUP = 2k to VDD, VDD = 3.3V, TA = TMIN to TMAX, unless otherwise noted.)
ON-RESISTANCE vs. VCM
MAX9940 toc01
MAX9940
ON-RESISTANCE vs. VCM
MAX9940 toc02
TURN-ON/TURN-OFF TIME vs. TEMPERATURE
MAX9940 toc03
60 50 ON-RESISTANCE () VCC = 2.5V 40 VCC = 3.3V 30 20 10 0 0 1 2 3 VCM (V) 4 5 6 VCC = 5.5V
60 50 ON-RESISTANCE () 40 30 20 TA = +25C 10 TA = -40C 0 0 0.5 1.0 1.5 2.0 VCM (V) 2.5 3.0 3.5 TA = +125C TA = +85C
300 TURN-ON/TURN-OFF TIME (ns) 250 200 150 100 50 0 TURN-OFF EXT = 0 TO 10V SQUARE WAVE RPULLUP = 200 -50 -25 0 25 50 75 TURN-ON
4.0
100 125 150
TEMPERATURE (C)
TURN-ON/TURN-OFF TIME vs. TEMPERATURE
MAX9940 toc04
SUPPLY CURRENT vs. SUPPLY VOLTAGE
MAX9940 toc05
INSERTION LOSS vs. FREQUENCY
2 1 INSERTION LOSS (dB) 0 -1 -2 -3 -4 -5 -6 -7
MAX9940 toc06
300 TURN-ON/TURN-OFF TIME (ns) 250 200 150 100 50 0 -50 -25 0 25 50 75 EXT = 0 TO 16V SQUARE WAVE RPULLUP = 200 TURN-OFF TURN-ON
16.0 15.5 SUPPLY CURRENT (A) 15.0 14.5 14.0 13.5 13.0 12.5 12.0 TA = +25C TA = -40C TA = +125C TA = +85C
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100 125 150
2.0
2.5
3.0
3.5
4.0
4.5
5.0
5.5
6.0
1k
10k
100k
1M
10M
100M
TEMPERATURE (C)
SUPPLY VOLTAGE (V)
FREQUENCY (Hz)
OFF-ISOLATION vs. FREQUENCY
MAX9940 toc07
FAULT TURN-ON AND RECOVERY TIME
MAX9940 toc08
0 -20 OFF-ISOLATION (dB) -40 -60 -80 -100
EXT 1V/div
0
INT 500mV/div VDD = VCC = 3.3V
-120 1k 10k 100k 1M 10M 100M FREQUENCY (Hz)
0 TIME (40s/div)
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Signal-Line Overvoltage Protector for Low-Voltage Devices MAX9940
Typical Operating Characteristics (continued)
(VCC = +3.3V, RINT_PULLUP = 2k to VDD, VDD = 3.3V, TA = TMIN to TMAX, unless otherwise noted.)
FAULT TURN-ON TIME
MAX9940 toc09
FAULT RECOVERY TIME
RPULLUP = 2k EXT 5V/div 0
MAX9940 toc10
RPULLUP = 200 EXT 5V/div 0
INT 2V/div
INT 500mV/div
0 TIME (100ns/div)
0 TIME (100ns/div)
FAULT TURN-ON AND RECOVERY TIME (SCHOTTKY DIODE FROM INT TO VCC)
RPULLUP = 2 EXT 5V/div 0
MAX9940 toc11
FAULT TURN-ON TIME (SCHOTTKY DIODE FROM INT TO VCC)
MAX9940 toc12
EXT 5V/div 0
INT 1V/div 0 TIME (40s/div)
INT 1V/div 0 TIME (100ns/div)
VTHR AND VTHF vs. SUPPLY VOLTAGE
MAX9940 toc13
VTHR AND VTHF vs. TEMPERATURE
VTHR 250 VOLTAGE THRESHOLD (mV) 200 150 100 50 0 VTHF
MAX9940 toc14
300 250 VOLTAGE THRESHOD (mV) 200 150 100 50 0 2.0 2.5 3.0
VTHR
300
VTHF
3.5
4.0
4.5
5.0
5.5
6.0
-50
-25
0
25
50
75
100
125
SUPPLY VOLTAGE (V)
TEMPERATURE (C)
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Signal-Line Overvoltage Protector for Low-Voltage Devices
Pin Description
PIN 1 2 3 4 5 NAME VCC GND N.C. INT EXT Ground No Connection. Not internally connected. Microcontroller I/O Port. Connection to a microcontroller data port. External Connector Port. Connection to a 1-Wire device. FUNCTION Power Supply. Can be connected to a microcontroller enable input.
MAX9940
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 resistance and capacitances cannot be used to provide protection due to their impact on VIL/VIH levels 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.
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 comparator 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 VCC trigger 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 withstand large DC voltages up to 28V at INT and EXT even when VCC is 0. This allows application-specific powersaving 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 VCC being connected directly to VDD of the microcontroller.
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 resistance is 38 (typ). The series switch is composed of parallel DMOS and HV-pMOS devices as shown in the
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Signal-Line Overvoltage Protector for Low-Voltage Devices MAX9940
VDD = 3.3V
ENABLE
VCC
MICROCONTROLLER RP 2k MAX9940 DATA Rx INT GND Tx Tx EXT 1-Wire DEVICE Rx
Figure 1. Recommended Scheme for Battery-Operated Devices that Need to Shut Down the MAX9940 and Prevent Power Draw During Short to GND Faults
In all three schemes, the MAX9940 protects the microcontroller from both DC fault voltages above VCC and 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 batteryoperated 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 microcontroller supplies the quiescent current for the MAX9940 as well as that required for digital communication (i.e., RP pullup 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 maintains the ability to withstand DC voltages up to 28V even when VCC = 0. In Figure 2, the ENABLE port of a microcontroller powers the MAX9940. The low 13A operating current allows standard digital I/O ports to easily supply the
operating current of the MAX9940 without any substantial 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 VDD even though VCC = 0, thus drawing no current from RP or 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 potentially reduce battery life. In Figure 3, VDD powers 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 VDD and potentially reducing battery life.
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Signal-Line Overvoltage Protector for Low-Voltage Devices MAX9940
VDD = 3.3V
ENABLE
VCC
MICROCONTROLLER RP 2k MAX9940 DATA Rx INT GND Tx Tx EXT 1-Wire DEVICE Rx
Figure 2. Recommended Scheme for Applications that Require the MAX9940 to be Put into Shutdown
VDD = 3.3V
VCC
MICROCONTROLLER RP 2k
MAX9940
DATA Rx INT GND Tx Tx EXT 1-Wire DEVICE Rx
Figure 3. Recommended Operating Circuit for Nonbattery-Operated Applications
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Signal-Line Overvoltage Protector for Low-Voltage Devices MAX9940
Pin Configuration
PROCESS: BiCMOS
TOP VIEW +
VCC 1 5 EXT
Chip Information
GND 2
MAX9940
N.C. 3
4
INT
SC70
8
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Signal-Line Overvoltage Protector for Low-Voltage Devices
Package Information
For the latest package outline information and land patterns, go to www.maxim-ic.com/packages. PACKAGE TYPE 5 SC70 PACKAGE CODE X5-1 DOCUMENT NO. 21-0076
SC70, 5L.EPS
MAX9940
PACKAGE OUTLINE, 5L SC70
21-0076
E
1 1
Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.
Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 _____________________ 9
(c) 2009 Maxim Integrated Products Maxim is a registered trademark of Maxim Integrated Products, Inc.

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