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LM74 SPI/MICROWIRE 12-Bit Plus Sign Temperature Sensor
July 2000
LM74 SPI/MICROWIRETM 12-Bit Plus Sign Temperature Sensor
General Description
The LM74 is a temperature sensor, Delta-Sigma analog-to-digital converter with an SPI and MICROWIRE compatible interface. The host can query the LM74 at any time to read temperature. A shutdown mode decreases power consumption to less than 10 A. This mode is useful in systems where low average power consumption is critical. The LM74 has 12-bit plus sign temperature resolution (0.0625C per LSB) while operating over a temperature range of -55C to +150C. The LM74's 3.0V to 5.5V supply voltage range, low supply current and simple SPI interface make it ideal for a wide range of applications. These include thermal management and protection applications in hard disk drives, printers, electronic test equipment, and office electronics. The LM74 is available in the SO-8 package as well as an 5-Bump micro SMD package. n Office Electronics n Electronic Test Equipment
Features
n 0.0625C temperature resolution. n Shutdown mode conserves power between temperature reading n SPI and MICROWIRE Bus interface n 5-Bump micro SMD package saves space
Key Specifications
h Supply Voltage h Supply Current
3.0V or 2.65V to 5.5V operating shutdown 265A (typ) 520A (max) 3A (typ)
Applications
n System Thermal Management n Personal Computers n Disk Drives
h Temperature
-10C to 65C -25C to 110C -55C to 125C
Accuracy
1.25C(max) 2.1C(max) 3C(max)
Simplified Block Diagram
DS100909-1
MICROWIRE (R) is a registered trademark of National Semiconductor Corporation.
(c) 2000 National Semiconductor Corporation
DS100909
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LM74
Connection Diagram
SO-8 5-Bump micro SMD
DS100909-2
TOP VIEW NS Package Number M08A
DS100909-24
Note: - Pin numbers are referenced to the package marking text orientation. Pin 1 is designated by the square. - Reference JEDEC Registration MO-211, variation BC - The top 4 characters designate the date code. The bottom 3 characters designate the device type (see ordering information).
TOP VIEW NS Package Number BPD05MPB
Ordering Information
Order Number LM74CIM-3 LM74CIMX-3 LM74CIM-5 LM74CIMX-5 LM74CIBP-3 LM74CIBPX-3 LM74CIBP-5 LM74CIBPX-5 Package Marking LM74CIM-3 LM74CIM-3 LM74CIM-5 LM74CIM-5 T8 T8 T9 T9 NS Package Number SO-8, M08A SO-8, M08A SO-8, M08A SO-8, M08A micro SMD, BPD05MPB micro SMD, BPD05MPB micro SMD, BPD05MPB micro SMD, BPD05MPB Supply Voltage 3.0V to 3.6V 3.0V to 3.6V 4.5V to 5.5V 4.5V to 5.5V 2.65V to 3.6V 2.65V to 3.6V 4.5V to 5.5V 4.5V to 5.5V Transport Media 95 Units in Rail 2500 Units in Tape and Reel 95 Units in Rail 2500 Units in Tape and Reel 250 Units in Tape and Reel 3000 Units in Tape and Reel 250 Units in Tape and Reel 3000 Units in Tape and Reel
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LM74
Pin Descriptions
Label SO-8 Pin # 1 2 3 4 5 6 7 8 3 2 4 micro SMD Pin # 1 5 Function Typical Connection
SI/O SC NC GND NC NC CS V+
Slave Input/Output - Serial bus bi-directional data line. Shmitt trigger input. Slave Clock - Serial bus clock Shmitt trigger input line. No Connection Power Supply Ground No Connection No Connection Chip Select input. Positive Supply Voltage Input
From and to Controller From Controller No Connection Ground No Connection No Connection From Controller DC Voltage from 3.0V to 5.5V for the LM74CIM and 2.65V to 5.5V for the LM74CIBP. Bypass with a 0.1 F ceramic capacitor.
Typical Application
DS100909-3
FIGURE 1. COP Microcontroller Interface
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Absolute Maximum Ratings (Note 1)
Supply Voltage -0.3V to 6.0V Voltage at any Pin -0.3V to V+ + 0.3V Input Current at any Pin (Note 2) 5 mA Package Input Current (Note 2) 20 mA Storage Temperature -65C to +150C Soldering Information, Lead Temperature SO-8 Package (Note 3) Vapor Phase (60 seconds) 215C Infrared (15 seconds) 220C ESD Susceptibility (Note 4)
Human Body Mode LM74CIBP SC, pin 5 LM74CIM and LM74CIBP all other pins Machine Model
1900V 2000V 200V
Operating Ratings
Specified Temperature Range (Note 5) LM74CIBP LM74CIM Supply Voltage Range (+VS) LM74CIBP LM74CIM TMIN to TMAX -40C to +125C -55C to +150C +2.65V to +5.5V +3.0V to +5.5V
Temperature-to-Digital Converter Characteristics
Unless otherwise noted, these specifications apply for V+ = 2.65V to 3.6V for the LM74CIBP -3, V+ = 3.0V to 3.6V for the LM74CIM -3 and V+ = 4.5V to 5.5V for the LM74 -5 (Note 6). Boldface limits apply for TA = TJ = TMIN to TMAX; all other limits TA = TJ =+25C, unless otherwise noted. Parameter Temperature Error (Note 6) Conditions TA = -10C to +65C TA = -25C to +110C TA = -40C to +85C TA = -40C to +110C TA = -55C to +125C TA = -55C to +150C Resolution Temperature Conversion Time Quiescent Current SO-8 (Note 9) micro SMD (Note 9) SO-8 Serial Bus Inactive micro SMD SO-8 Serial Bus Active micro SMD SO-8 Shutdown Mode, V+ = 3.3V micro SMD SO-8 Shutdown Mode, V+ = 5V micro SMD 13 280 611 310 265 310 310 7 3 8 4 425 925 520 470 425 925 520 470 Typical (Note 7) LM74-5 Limits (Note 8) LM74-3 Limits (Note 8) Units (Limit) C (max) C (max) C (max) C (max) C (max) C (max) Bits ms (max) ms (max) A (max) A (max) A A A A A A
1.25 2.1
+2.65/-1.65 +2.65/ -2.0
1.25
+2.65/-2.15
2.15
+2.65/-2.15
3.0 5.0
3.5 5.0
Logic Electrical Characteristics
DIGITAL DC CHARACTERISTICS Unless otherwise noted, these specifications apply for V+ = 2.65V to 3.6V for the LM74CIBP -3, V+ = 3.0V to 3.6V for the LM74CIM -3 and V+ = 4.5V to 5.5V for the LM74 -5 (Note 6). Boldface limits apply for TA = TJ = TMIN to TMAX; all other limits TA = TJ =+25C, unless otherwise noted. Symbol VIN(1) VIN(0) Parameter Logical "1" Input Voltage Logical "0" Input Voltage Input Hysteresis Voltage IIN(1) IIN(0) Logical "1" Input Current Logical "0" Input Current V+ = 3.0V to 3.6V V = 4.5V to 5.5V VIN = V+ VIN = 0V
+
Conditions
Typical (Note 7)
Limits (Note 8) V+ x 0.7 V + 0.3 -0.3 V+ x 0.3
+
Units (Limit) V (min) V (max) V (min) V (max) V (min) V (min) A (max) A (min)
0.8 0.8 0.005 -0.005
0.35 0.33 3.0 -3.0
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Logic Electrical Characteristics
(Continued)
DIGITAL DC CHARACTERISTICS Unless otherwise noted, these specifications apply for V+ = 2.65V to 3.6V for the LM74CIBP -3, V+ = 3.0V to 3.6V for the LM74CIM -3 and V+ = 4.5V to 5.5V for the LM74 -5 (Note 6). Boldface limits apply for TA = TJ = TMIN to TMAX; all other limits TA = TJ =+25C, unless otherwise noted. Symbol CIN VOH VOL IO_TRI-STATE Parameter All Digital Inputs High Level Output Voltage Low Level Output Voltage TRI-STATE Output Leakage Current IOH = -400 A IOL = +2 mA VO = GND VO = V + Conditions Typical (Note 7) 20 2.4 0.4 -1 +1 Limits (Note 8) Units (Limit) pF V (min) V (max) A (min) A(max)
SERIAL BUS DIGITAL SWITCHING CHARACTERISTICS Unless otherwise noted, these specifications apply for V+ = 2.65V to 3.6V for the LM74CIBP -3, V+ = 3.0V to 3.6V for the LM74CIM -3 and V+ = 4.5V to 5.5V for the LM74 -5 (Note 6); CL (load capacitance) on output lines = 100 pF unless otherwise specified. Boldface limits apply for TA = TJ = TMIN to TMAX; all other limits TA = TJ = +25C, unless otherwise noted. Symbol t1 t2 t3 t4 t5 t6 t7 SC (Clock) Period CS Low to SC (Clock) High Set-Up Time CS Low to Data Out (SO) Delay SC (Clock) Low to Data Out (SO) Delay CS High to Data Out (SO) TRI-STATE SC (Clock) High to Data In (SI) Hold Time Data In (SI) Set-Up Time to SC (Clock) High Parameter Conditions Typical (Note 7) Limits (Note 8) 0.16 DC 100 70 100 200 50 30 Units (Limit) s (min) (max) ns (min) ns (max) ns (max) ns (max) ns (min) ns (min)
DS100909-4
FIGURE 2. Data Output Timing Diagram
DS100909-5
FIGURE 3. TRI-STATE Data Output Timing Diagram
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LM74
Logic Electrical Characteristics
(Continued)
DS100909-6
FIGURE 4. Data Input Timing Diagram
Note 1: Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. DC and AC electrical specifications do not apply when operating the device beyond its rated operating conditions. Note 2: When the input voltage (VI) at any pin exceeds the power supplies (VI < GND or VI > +VS) the current at that pin should be limited to 5 mA. The 20 mA maximum package input current rating limits the number of pins that can safely exceed the power supplies with an input current of 5 mA to four. Note 3: See AN-450 "Surface Mounting Methods and Their Effect on Product Reliability" or the section titled "Surface Mount" found in a current National Semiconductor Linear Data Book for other methods of soldering surface mount devices. Note 4: Human body model, 100 pF discharged through a 1.5 k resistor. Machine model, 200 pF discharged directly into each pin. Note 5: The life expectancy of the LM74 will be reduced when operating at elevated temperatures. LM74 JA (thermal resistance, junction-to-ambient) when attached to a printed circuit board with 2 oz. foil is summarized in the table below:
Device Number LM74CIM LM74CIBP
NS Package Number M08A BPD05MPB
Thermal Resistance (JA) 160C/W 250C/W
Note 6: All SOP (LM74CIM) parts will function over the V+ supply voltage range of 3V to 5.5V. All micro SMD (LM74SIBP) parts will function over the V+ supply voltage range of 2.65V to 5.5V. The SOP (LM74CIM) parts are tested and specified for rated temperature error at their nominal supply voltage for temperature ranges of -10C to +65C, -55C to +125C and -55C to +150C. For the SOP (LM74CIM) parts the temperature error specifications for temperature ranges of -40C to +85C, -25C to +110C and -40C to +110C include error induced by power supply variation of 5% from the nominal value. For the LM74CIM (SOP) parts the temperature error will increase by 0.3C for a power supply voltage (V+) variation of 10% from the nominal value. For the LM74CIBP-3 (micro SMD) parts all accuracies are guaranteed over the supply range of 2.65V to 3.6V, except for the temperature ranges of -55C to 125C and -55C to +150C where the accuracy applies for the nominal supply voltage of 3.3V. For the LM74CIBP-5 (micro SMD) parts all accuracies are guranteed over the supply range of 4.75V to 5.25V, except for the temperature ranges of -55C to 125C and -55C to +150C where the accuracy applies for the nominal supply voltage of 5.0V. For the LM74CIBP over -55C to 125C and -55C to +150C, a power supply variation of 10% will degrade the accuracy by 0.3C. Note 7: Typicals are at TA = 25C and represent most likely parametric norm. Note 8: Limits are guaranteed to National's AOQL (Average Outgoing Quality Level). Note 9: This specification is provided only to indicate how often temperature data is updated. The LM74 can be read at any time without regard to conversion state (and will yield last conversion result). A conversion in progress will not be interrupted. The output shift register will be updated at the completion of the read and a new conversion restarted. Note 10: For best accuracy, minimize output loading. Higher sink currents can affect sensor accuracy with internal heating. This can cause an error of 0.64C at full rated sink current and saturation voltage based on junction-to-ambient thermal resistance.
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Electrical Characteristics
DS100909-8
FIGURE 5. Temperature-to-Digital Transfer Function (Non-linear scale for clarity)
TRI-STATE Test Circuit
DS100909-7
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LM74
Typical Performance Characteristics
Average Power-On Reset Voltage vs Temperature Static Supply Current vs Temperature (SO-8)
DS100909-23
DS100909-21
Static Supply Current vs Temperature (micro SMD)
Temperature Error (SO-8)
DS100909-25 DS100909-22
1.0 Functional Description
The LM74 temperature sensor incorporates a band-gap type temperature sensor and 12-bit plus sign ADC (Delta-Sigma Analog-to-Digital Converter). Compatibility of the LM74's three wire serial interface with SPI and MICROWIRE allows simple communications with common microcontrollers and processors. Shutdown mode can be used to optimize current drain for different applications. A Manufacture's/Device ID register identifies the LM74 as National Semiconductor product. 1.1 POWER UP AND POWER DOWN The LM74 always powers up in a known state. The power up default condition is continuous conversion mode. Immediatly after power up the LM74 will output an erroneous code until the first temperature conversion has completed. When the supply voltage is less than about 1.6V (typical), the LM74 is considered powered down. As the supply voltage rises above the nominal 1.6V power up threshold, the internal registers are reset to the power up default state described above. 1.2 SERIAL BUS INTERFACE The LM74 operates as a slave and is compatible with SPI or MICROWIRE bus specifications. Data is clocked out on the falling edge of the serial clock (SC), while data is clocked in on the rising edge of SC. A complete transmit/receive communication will consist of 32 serial clocks. The first 16 clocks comprise the transmit phase of communication, while the second 16 clocks are the receive phase. When CS is high SI/O will be in TRI-STATE (R) . Communication should be initiated by taking chip select (CS) low. This should not be done when SC is changing from a low to high state. Once CS is low the serial I/O pin (SI/O) will transmit the first bit of data. The master can then read this bit with the rising edge of SC. The remainder of the data will be clocked out by the falling edge of SC. Once the 14 bits of data (one sign bit, twelve temperature bits and 1 high bit) are transmitted the SI/O line will go into TRI-STATE. CS can be taken high at any time during the transmit phase. If CS is brought low in the middle of a conversion the LM74 will complete the conversion and the output shift register will be updated after CS is brought back high.
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LM74
1.0 Functional Description
(Continued)
1.3 TEMPERATURE DATA FORMAT Temperature data is represented by a 13-bit, two's complement word with an LSB (Least Significant Bit) equal to 0.0625C: Temperature +150C +125C +25C +0.0625C 0C -0.0625C -25C -55C Digital Output Binary 0100 1011 0000 0111 0011 1110 1000 0111 0000 1100 1000 0111 0000 0000 0000 1111 0000 0000 0000 0111 1111 1111 1111 1111 1111 0011 1000 0111 1110 0100 1000 0111 Hex 4B 07h 3E 87h 0B 87h 00 0Fh 00 07h FF FFh F3 87h E4 87h
The receive phase of a communication starts after 16 SC periods. CS can remain low for 32 SC cycles. The LM74 will read the data available on the SI/O line on the rising edge of the serial clock. Input data is to an 8-bit shift register. The part will detect the last eight bits shifted into the register. The receive phase can last up to 16 SC periods. All ones must be shifted in order to place the part into shutdown. A zero in any location will take the LM74 out of shutdown. The following codes should only be transmitted to the LM74:
* 00 hex * 01 hex * 03 hex * 07 hex * 0F hex * 1F hex * 3F hex * 7F hex * FF hex any others may place the part into a Test Mode. Test Modes are used by National Semiconductor to thoroughly test the function of the LM74 during production testing. Only eight bits have been defined above since only the last eight transmitted are detected by the LM74, before CS is taken HIGH. The following communication can be used to determine the Manufacturer's/Device ID and then immediately place the part into continuous conversion mode. With CS continuously low: * Read 16 bits of temperature data * Write 16 bits of data commanding shutdown * Read 16 bits of Manufacture's/Device ID data * Write 8 to 16 bits of data commanding Conversion Mode * Take CS HIGH. Note that 250 ms will have to pass for a conversion to complete before the LM74 actually transmits temperature data.
Note: The last two bits are TRI-STATE and depicted as one in the table. The first data byte is the most significant byte with most significant bit first, permitting only as much data as necessary to be read to determine temperature condition. For instance, if the first four bits of the temperature data indicate an overtemperature condition, the host processor could immediately take action to remedy the excessive temperatures. 1.4 SHUTDOWN MODE/MANUFACTURER'S ID Shutdown mode is enabled by writing XX FF to the LM74 as shown in Figure 7c. The serial bus is still active when the LM74 is in shutdown. Current draw drops to less than 10 A between serial communications. When in shutdown mode the LM74 always will output 1000 0000 0000 0XX. This is the manufacturer's/Device ID information. The first 5-bits of the field (1000 0XXX) are reserved for manufacturer's ID.
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LM74
1.0 Functional Description
1.5 INTERNAL REGISTER STRUCTURE
(Continued)
The LM74 has three registers, the temperature register, the configuration register and the manufacturer's/device identifi1.5.1 CONFIGURATION REGISTER (Selects shutdown or continuous conversion modes): (Write Only): D15 X D14 X D13 X D12 X D11 X D10 X D9 X D8 X
cation register. The temperature and manufacturer's/device identification registers are read only. The configuration register is write only.
D7
D6
D5
D4
D3
D2
D1
D0
Shutdown
D0-D15 set to XX FF hex enables shutdown mode. D0-D15 set to 00 00 hex sets Continuous conversion mode. Note: setting D0-D15 to any other values may place the LM70 into a manufacturer's test mode, upon which the LM74 will stop responding as described. These test modes are to be used for National Semiconductor production testing only. See Section 1.2 Serial Bus Interface for a complete discussion. 1.5.2 TEMPERATURE REGISTER (Read Only): D15 MSB D14 Bit 11 D13 Bit 10 D12 Bit 9 D11 Bit 8 D10 Bit 7 D9 Bit 6 D8 Bit 5 D7 Bit 4 D6 Bit 3 D5 Bit 2 D4 Bit 1 D3 LSB D2 1 D1 X D0 X
D0-D1: Undefined. TRI-STATE will be output on SI/0. D2: Always set high. D3-D15: Temperature Data. One LSB = 0.0625C. Two's complement format. 1.5.3 MANUFACTURER'S/DEVICE ID REGISTER (Read Only): D15 1 D14 0 D13 0 D12 0 D11 0 D10 0 D9 0 D8 0 D7 0 D6 0 D5 0 D4 0 D3 0 D2 0 D1 X D0 X
D0-D1: Undefined. TRI-STATE will be output on SI/0. D2-D15: Manufacturer's/Device ID Data. This register is accessed whenever the LM74 is in shutdown mode.
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2.0 Serial Bus Timing Diagrams
DS100909-14
a) Reading Continuous Conversion - Single Eight-Bit Frame
DS100909-15
b) Reading Continuous Conversion - Two Eight-Bit Frames
DS100909-18
c) Writing Shutdown Control FIGURE 7. Timing Diagrams
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3.0 Application Hints
To get the expected results when measuring temperature with an integrated circuit temperature sensor like the LM74, it is important to understand that the sensor measures its own die temperature. For the LM74, the best thermal path between the die and the outside world is through the LM74's pins. In the SO-8 package all the pins on the LM74 will have an equal effect on the die temperature. Because the pins represent a good thermal path to the LM74 die, the LM74 will provide an accurate measurement of the temperature of the printed circuit board on which it is mounted. There is a less efficient thermal path between the plastic package and the LM74 die. If the ambient air temperature is significantly different from the printed circuit board temperature, it will have a small effect on the measured temperature. In probe-type applications, the LM74 can be mounted inside a sealed-end metal tube, and can then be dipped into a bath or screwed into a threaded hole in a tank. As with any IC, the LM74 and accompanying wiring and circuits must be kept insulated and dry, to avoid leakage and corrosion. This is especially true if the circuit may operate at cold temperatures
where condensation can occur. Printed-circuit coatings and varnishes such as Humiseal and epoxy paints or dips are often used to insure that moisture cannot corrode the LM74 or its connections.
3.1 micro SMD LIGHT SENSITIVITY
The LM74 in the micro SMD package should not be exposed to ultraviolet light. The micro SMD package does not completely encapsulate the LM74 die in epoxy. Exposing the LM74 micro SMD package to bright sunlight will not immediatly cause a change in the output reading. Our experiments show that directly exposing the circuit side (bump side) of the die to high intensity ( 1mW/cm2) ultraviolet light, centered at a wavelength of 254nm, for greater than 20 minutes will deprogram the EEPROM cells in the LM74. Since the EEPROM is used for storing calibration coefficients, the LM74 will function but the temperature accuracy will no longer be as specified. Light can penetrate through the side of the package as well, so exposure to ultra violet radiation is not recommended even after mounting.
4.0 Typical Applications
DS100909-20
FIGURE 8. Temperature monitor using Intel 196 processor
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4.0 Typical Applications
(Continued)
DS100909-19
FIGURE 9. LM74 digital input control using micro-controller's general purpose I/O.
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LM74
Physical Dimensions
inches (millimeters) unless otherwise noted
8-Lead Molded Small Outline Package Order Number LM74CIM-3, LM74CIMX-3, LM74CIM-5 or LM74CIMX-5 NS Package Number M08A
5-Bump micro SMD Ball Grid Array Package Order Number LM74CIBP-3,LM74CIBPX-3, LM74CIBP-5, LM74CIBPX-5 NS Package Number BPD05MPB The following dimensions apply to the BPD05MPB package shown above: X1=1565m 30m, X2=1615m 30m, X3=850m 50m.
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LM74 SPI/MICROWIRE 12-Bit Plus Sign Temperature Sensor
Notes
LIFE SUPPORT POLICY NATIONAL'S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT DEVICES OR SYSTEMS WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT AND GENERAL COUNSEL OF NATIONAL SEMICONDUCTOR CORPORATION. As used herein: 1. Life support devices or systems are devices or systems which, (a) are intended for surgical implant into the body, or (b) support or sustain life, and whose failure to perform when properly used in accordance with instructions for use provided in the labeling, can be reasonably expected to result in a significant injury to the user.
National Semiconductor Corporation Americas Tel: 1-800-272-9959 Fax: 1-800-737-7018 Email: support@nsc.com www.national.com National Semiconductor Europe Fax: +49 (0) 180-530 85 86 Email: europe.support@nsc.com Deutsch Tel: +49 (0) 69 9508 6208 English Tel: +44 (0) 870 24 0 2171 Francais Tel: +33 (0) 1 41 91 8790
2. A critical component is any component of a life support device or system whose failure to perform can be reasonably expected to cause the failure of the life support device or system, or to affect its safety or effectiveness.
National Semiconductor Asia Pacific Customer Response Group Tel: 65-2544466 Fax: 65-2504466 Email: ap.support@nsc.com
National Semiconductor Japan Ltd. Tel: 81-3-5639-7560 Fax: 81-3-5639-7507
National does not assume any responsibility for use of any circuitry described, no circuit patent licenses are implied and National reserves the right at any time without notice to change said circuitry and specifications.

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