LM77CIMM-5

LM77 9-Bit + Sign Digital Temperature Sensor and Thermal Window Comparator with Two-Wire Interface July 2001 LM77 9-Bit + Sign Digital Temperature Sensor and Thermal Window Comparator with Two-Wire Interface General Description The LM77 is a digital temperature sensor and thermal window comparator with an I2C™ Serial Bus interface. The window-comparator architecture of the LM77 eases the design of temperature control systems conforming to the ACPI (Advanced Configuration and Power Interface) specification for personal computers. The open-drain Interrupt (INT) output becomes active whenever temperature goes outside a programmable window, while a separate Critical Temperature Alarm (T_CRIT_A) output becomes active when the temperature exceeds a programmable critical limit. The INT output can operate in either a comparator or event mode, while the T_CRIT_A output operates in comparator mode only. The host can program both the upper and lower limits of the window as well as the critical temperature limit. Programmable hysterisis as well as a fault queue are available to minimize false tripping. Two pins (A0, A1) are available for address selection. The sensor powers up with default thresholds of 2˚C THYST, 10˚C TLOW, 64˚C THIGH, and 80˚C T_CRIT. The LM77’s 3.0V to 5.5V supply voltage range, Serial Bus interface, 9-bit + sign output, and full-scale range of over 128˚C make it ideal for a wide range of applications. These include thermal management and protection applications in personal computers, electronic test equipment, office electronics, automotive, and HVAC applications. Features n Window comparison simplifies design of ACPI compatible temperature monitoring and control. n Serial Bus interface n Separate open-drain outputs for Interrupt and Critical Temperature shutdown n Shutdown mode to minimize power consumption n Up to 4 LM77s can be connected to a single bus n 9-bit + sign output; full-scale reading of over 128˚C n SOP and MSOP 8-lead packages Key Specifications j Supply Voltage j Supply Current 3.0V to 5.5V operating shutdown 250 µA (typ) 500 µA (max) 5 µA (typ) j Temperature Accuracy −10˚C to 65˚C −25˚C to 100˚C −55˚C to 125˚C ± 1.5˚C(max) ± 2˚C(max) ± 3˚C(max) Applications n n n n n n System Thermal Management Personal Computers Office Electronics Electronic Test Equipment Automotive HVAC I2C ® is a registered trademark of Philips Corporation. © 2001 National Semiconductor Corporation DS100136 www.national.com LM77 Simplified Block Diagram DS100136-1 Connection Diagram SOP8 or MSOP DS100136-2 LM77 See NS Package Number M08A or MM08A Ordering Information Order Number LM77CIM-3 LM77CIMX-3 LM77CIM-5 LM77CIMX-5 LM77CIMM-3 LM77CIMMX-3 LM77CIMM-5 LM77CIMMX-5 Supply Voltage 3.3V 3.3V 5V 5V 3.3V 3.3V 5V 5V Package SOP8, M08A SOP8, M08A SOP8, M08A SOP8, M08A MSOP8, MUA08A MSOP8, MUA08A MSOP8, MUA08A MSOP8, MUA08A Rail 2500 Units on Tape and Reel Rail 2500 Units on Tape and Reel Rail 3500 Units on Tape and Reel Rail 3500 Units on Tape and Reel Supplied In Pin Description Label SDA SCL T_CRIT_A GND INT +VS A0–A1 Pin # 1 2 3 4 5 8 7,6 Function Serial Bi-Directional Data Line. Open Drain Output Serial Bus Clock Input Critical Temperature Alarm Open Drain Output Power Supply Ground Interrupt Open Drain Output Positive Supply Voltage Input User-Set Address Inputs Typical Connection From Controller From Controller Pull Up Resistor, Controller Interrupt Line or System Hardware Shutdown Ground Pull Up Resistor, Controller Interrupt Line DC Voltage from 3V to 5.5V Ground (Low, “0”) or +VS (High, “1”) www.national.com 2 LM77 Pin Description (Continued) DS100136-3 FIGURE 1. Typical Application 3 www.national.com LM77 Absolute Maximum Ratings (Note 1) Supply Voltage Voltage at any Pin Input Current at any Pin Package Input Current (Note 2) T_CRIT_A and INT Output Sink Current T_CRIT_A and INT Output Voltage Storage Temperature −0.3V to 6.5V −0.3V to (+VS + 0.3V ) 5 mA 20 mA 10 mA 6.5V −65˚C to +125˚C Soldering Information, Lead Temperature SOP and MSOP Package (Note 3) Vapor Phase (60 seconds) Infrared (15 seconds) ESD Susceptibility (Note 4) Human Body Model Machine Model 215˚C 220˚C 2500V 250V Operating Ratings (Notes 1, 5) Specified Temperature Range (Note 6) Supply Voltage Range (+VS)(Note 7) T MIN to TMAX −55˚C to +125˚C +3.0V to +5.5V Temperature-to-Digital Converter Characteristics Unless otherwise noted, these specifications apply for +VS =+5 Vdc ± 10% for LM77CIM-5, LM77CIMM-5 and +VS =+3.3 Vdc ± 10% for LM77CIM-3, LM77CIMM-3 (Note 7). Boldface limits apply for TA = TJ = TMIN to TMAX; all other limits TA = TJ =+25˚C, unless otherwise noted. Parameter Accuracy Conditions TA = −10˚C to +65˚C TA = −25˚C to +100˚C TA = −55˚C to +125˚C Resolution Temperature Conversion Time Quiescent Current (Note 10) (Note 11) I2C Inactive I2C Active Shutdown Mode THYST Default Temperature TLOW Default Temperature THIGH Default Temperature TC Default Temperature (Notes 13, 14) (Note 14) (Note 14) (Note 14) 10 0.5 70 0.25 0.25 5 2 10 64 80 0.5 10 125 Typical (Note 8) Limits (Note 9) Units (Limit) ˚C (max) Bits ˚C ms mA mA (max) µA ˚C ˚C ˚C ˚C ± 1.5 ± 2.0 ± 3.0 Logic Electrical Characteristics DIGITAL DC CHARACTERISTICS Unless otherwise noted, these specifications apply for +VS =+5 Vdc ± 10% for LM77CIM-5, LM77CIMM-5 and +VS =+3.3 Vdc ± 10% for LM77CIM-3, LM77CIMM-3. Boldface limits apply for TA = TJ = TMIN to TMAX; all other limits TA = TJ =+25˚C, unless otherwise noted. Symbol VIN(1) Parameter SDA and SCL Logical “1” Input Voltage SDA and SCL Logical “0” Input Voltage A0 and A1 Logical “1” Input Voltage A0 and A1 Logical “0” Input Voltage Logical “1” Input Current Logical “0” Input Current Capacitance of All Digital Inputs 4 Conditions Typical (Note 8) Limits (Note 9) +VS x 0.7 +VS+0.3 Units (Limit) V (min) V (max) V (min) V (max) V (min) V (max) V (min) V (max) µA (max) µA (max) pF VIN(0) −0.3 +VS x 0.3 VIN(1) 2.0 +VS+0.3 VIN(0) −0.3 0.8 IIN(1) IIN(0) CIN www.national.com VIN = + VS VIN = 0V 0.005 −0.005 20 1.0 −1.0 LM77 Logic Electrical Characteristics (Continued) DIGITAL DC CHARACTERISTICS Unless otherwise noted, these specifications apply for +VS =+5 Vdc ± 10% for LM77CIM-5, LM77CIMM-5 and +VS =+3.3 Vdc ± 10% for LM77CIM-3, LM77CIMM-3. Boldface limits apply for TA = TJ = TMIN to TMAX; all other limits TA = TJ =+25˚C, unless otherwise noted. Symbol IOH VOL Parameter High Level Output Current Low Level Output Voltage T_CRIT_A Output Saturation Voltage T_CRIT_A Delay tOF Output Fall Time CL = 400 pF IO = 3 mA Conditions VOH = + VS IOL = 3 mA IOUT = 4.0 mA (Note 12) Typical (Note 8) Limits (Note 9) 10 0.4 0.8 1 250 Units (Limit) µA (max) V (max) V (max) Conversions (max) ns (max) 5 www.national.com LM77 Logic Electrical Characteristics (Continued) SERIAL BUS DIGITAL SWITCHING CHARACTERISTICS Unless otherwise noted, these specifications apply for +VS =+5 Vdc ± 10% for LM77CIM-5 and LM77CIMM-5, +VS =+3.3 Vdc ± 10% for LM77CIM-3 and LM77CIMM-3, CL (load capacitance) on output lines = 80 pF unless otherwise specified. Boldface limits apply for TA = TJ = TMIN to TMAX; all other limits TA = TJ = +25˚C, unless otherwise noted. The switching characteristics of the LM77 fully meet or exceed the published specifications of the I2C bus. The following parameters are the timing relationship between SCL and SDA signal related to the LM77. They are not the I2C bus specifications. Symbol t1 t2 t3 t4 t5 SCL (Clock) Period Data in Set-Up Time to SCL High Data Out Stable after SCL Low SDA Low Set-Up Time to SCL Low (Start Condition) SDA High Hold Time after SCL High (Stop Condition) Parameter Conditions Typical (Note 8) Limits (Note 9) 2.5 100 0 100 100 Units (Limit) µs(min) ns(min) ns(min) ns(min) ns(min) DS100136-4 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 kΩ resistor. Machine model, 200 pF discharged directly into each pin. Note 5: LM77 θJA (thermal resistance, junction-to-ambient) when attached to a printed circuit board with 2 oz. foil is: 200˚C/W for the SOP-8 (M08A) package, 250˚C/W for the MSOP-8 (MUA08A) package. Note 6: While the LM77 has a full-scale-range in excess of 128˚C, prolonged operation at temperatures above 125˚C is not recommended. Note 7: Both part numbers of the LM77 will operate properly over the +VS supply voltage range of 3V to 5.5V . The devices are tested and specified for rated accuracy at their nominal supply voltage. Accuracy will typically degrade 1˚C/V of variation in +VS as it varies from the nominal value. Note 8: Typicals are at TA = 25˚C and represent most likely parametric norm. Note 9: Limits are guaranteed to National’s AOQL (Average Outgoing Quality Level). Note 10: 9 bits + sign, two’s complement Note 11: This specification is provided only to indicate how often temperature data is updated. The LM77 can be read at any time without regard to conversion state (and will yield last conversion result). If a conversion is in process it will be interrupted and restarted after the end of the read. Note 12: For best accuracy, minimize output loading. Higher sink currents can affect sensor accuracy with internal heating. This can cause an error of 0.64˚C at full rated sink current and saturation voltage based on junction-to-ambient thermal resistance. Note 13: Hysteresis value adds to the TLOW setpoint value (e.g.: if TLOW setpoint = 10˚C, and hysteresis = 2˚C, then actual hysteresis point is 10+2 = 12˚C); and subtracts from the THIGH and T_CRIT setpoints (e.g.: if THIGH setpoint = 64˚C, and hysteresis = 2˚C, then actual hysteresis point is 64−2 = 62˚C). For a detailed discussion of the function of hysteresis refer to Section 1.1, TEMPERATURE COMPARISON, and Figure 3. Note 14: Default values set at power up. www.national.com 6 LM77 Logic Electrical Characteristics (Continued) DS100136-5 FIGURE 2. Temperature-to-Digital Transfer Function (Non-linear scale for clarity) 1.0 Functional Description The LM77 temperature sensor incorporates a band-gap type temperature sensor, 10-bit ADC, and a digital comparator with user-programmable upper and lower limit values. The comparator activates either the INT line for temperatures outside the TLOW and THIGH window, or the T_CRIT_A line for temperatures which exceed T_CRIT. The lines are programmable for mode and polarity. 1.1 TEMPERATURE COMPARISON LM77 provides a window comparison against a lower (TLOW) and upper (THIGH) trip point. A second upper trip point (T_CRIT) functions as a critical alarm shutdown. Figure 3 depicts the comparison function as well as the modes of operation. 1.1.1 STATUS BITS The internal Status bits operate as follows: “True”: Temperature above a THIGH or T_CRIT is “true” for those respective bits. A “true” for TLOW is temperature below TLOW. “False”: Assuming temperature has previously crossed above THIGH or T_CRIT, then the temperature must drop below the points corresponding THYST(THIGH − THYST or T_CRIT − THYST) in order for the condition to be false. For TLOW, assuming temperature has previously crossed below TLOW, a “false” occurs when temperature goes above TLOW + THYST. The Status bits are not affected by reads or any other actions, and always represent the state of temperature vs. setpoints. 1.1.2 HARDWIRE OUTPUTS The T_CRIT_A hardwire output mirrors the T_CRIT_A flag, when the flag is true, the T_CRIT_A output is asserted at all times regardless of mode. Reading the LM77 has no effect on the T_CRIT_A output, although the internal conversion is restarted. The behavior of the INT hardwire output is as follows: Comparator Interrupt Mode (Default): User reading part resets output until next measurement completes. If condition is still true, output is set again at end of next conversion cycle. For example, if a user never reads the part, and temperature goes below TLOW then INT becomes active. It would stay that way until temperature goes above TLOW + THYST. However if the user reads the part, the output would be reset. At the end of the next conversion cycle, if the condition is true, it is set again. If not, it remains reset. Event Interrupt Mode: User reading part resets output until next condition ″event″ occurs (in other words, output is only set once for a true condition, if reset by a read, it remains reset until the next triggering threshold has been crossed). Conversely, if a user never read the part, the output would stay set indefinitely after the first event that set the output. An “event” for Event Interrupt Mode is defined as: 1. Transitioning upward across a setpoint, or 2. Transitioning downward across a setpoint’s corresponding hysteresis (after having exceeded that setpoint). For example, if a user never read the part, and temperature went below TLOW then INT would become active. It would stay that way forever if a user never read the part. However if the user read the part, the output would be reset. Even if the condition is true, it will remain reset. The temperature must cross above TLOW + THYST to set the output again. In either mode, reading any register in the LM77 restarts the conversion. This allows a designer to know exactly when the LM77 begins a comparison. This prevents unnecessary In7 www.national.com LM77 1.0 Functional Description (Continued) Average Power on Reset Voltage vs Temperature terrupts just after reprogramming setpoints. Typically, system Interrupt inputs are masked prior to reprogramming trip points. By doing a read just after resetting trip points, but prior to unmasking, unexpected Interrupts are prevented. Avoid programming setpoints so close that their hysteresis values overlap. An example would be that with a THYST value of 2˚C then setting THIGH and TLOW to within 4˚C of each other will violate this restriction. To be more specific, with THYST set to 2˚C assume THIGH set to 64˚C. If TLOW is set equal to, or higher than 60˚C this restriction is violated. 1.2 DEFAULT SETTINGS The LM77 always powers up in a known state. LM77 power up default conditions are: 1. Comparator Interrupt Mode 2. TLOW set to 10˚C 3. 4. 5. THIGH set to 64˚C T_CRIT set to 80˚C THYST set to 2˚C DS100136-18 6. INT and T_CRIT_A active low 7. Pointer set to “00”; Temperature Register The LM77 registers will always reset to these default values when the power supply voltage is brought up from zero volts as the supply crosses the voltage level plotted in the following curve. The LM77 registers will reset again when the power supply drops below the voltage plotted in this curve. 1.3 SERIAL BUS INTERFACE The LM77 operates as a slave on the Serial Bus, so the SCL line is an input (no clock is generated by the LM77) and the SDA line is a bi-directional serial data line. According to Serial Bus specifications, the LM77 has a 7-bit slave address. The five most significant bits of the slave address are hard wired inside the LM77 and are “10010”. The two least significant bits of the address are assigned to pins A1–A0, and are set by connecting these pins to ground for a low, (0); or to +VS for a high, (1). Therefore, the complete slave address is: 1 MSB 0 0 1 0 A1 A0 LSB www.national.com 8 LM77 1.0 Functional Description (Continued) DS100136-6 Note: Event Interrupt mode is drawn as if the user is reading the part. If the user doesn’t read, the outputs would go low and stay that way until the LM77 is read. FIGURE 3. Temperature Response Diagram 1.4 TEMPERATURE DATA FORMAT Temperature data can be read from the Temperature and Set Point registers; and written to the Set Point registers. Temperature data can be read at any time, although reading faster than the conversion time of the LM77 will prevent data from being updated. Temperature data is represented by a 10-bit, two’s complement word with an LSB (Least Significant Bit) equal to 0.5˚C: Temperature +130˚C +125˚C +25˚C +0.5˚C 0˚C −0.5˚C −25˚C −55˚C Digital Output Binary 01 0000 0100 00 1111 1010 00 0011 0010 00 0000 0001 00 0000 0000 11 1111 1111 11 1100 1110 11 1001 0010 Hex 104h 0FAh 032h 001h 000h 3FFh 3CEh 392h 1.7 FAULT QUEUE A fault queue of up to 4 faults is provided to prevent false tripping when the LM77 is used in noisy environments. The 4 faults must occur consecutively to set flags as well as INT and T_CRIT_A outputs. The fault queue is enabled by setting bit 4 of the Configuration Register high (see Section 1.11). reset if previously set. Since conversions are stoped during shutdown, T_CRIT_A and INT will not be operational. The Serial Bus interface remains active. Activity on the clock and data lines of the Serial Bus may slightly increase shutdown mode quiescent current. Registers can be read from and written to in shutdown mode. The LM77 takes miliseconds to respond to the shutdown command. 1.6 INT AND T_CRIT_A OUTPUT The INT and T_CRIT_A outputs are open-drain outputs and do not have internal pull-ups. A ″high″ level will not be observed on these pins until pull-up current is provided from some external source, typically a pull-up resistor. Choice of resistor value depends on many system factors but, in general, the pull-up resistor should be as large as possible. This will minimize any errors due to internal heating of the LM77. The maximum resistance of the pull up, based on LM77 specification for High Level Output Current, to provide a 2 volt high level, is 30K ohms. 1.5 SHUTDOWN MODE Shutdown mode is enabled by setting the shutdown bit in the Configuration register via the Serial Bus. Shutdown mode reduces power supply current to 5 µA typical. T_CRIT_A is 9 www.national.com LM77 1.0 Functional Description 1.8 INTERNAL REGISTER STRUCTURE (Continued) DS100136-7 There are four data registers in the LM77, selected by the Pointer register. At power-up the Pointer is set to “00”; the location for the Temperature Register. The Pointer register latches the last location it was set to. In Interrupt Mode, a read from the LM77 resets the INT output. Placing the device in Shutdown mode resets the INT and T_CRIT_A outputs. All registers are read and write, except the Temperature register which is read only. A write to the LM77 will always include the address byte and the Pointer byte. A write to the Configuration register requires one data byte, while the TLOW, THIGH, and T_CRIT registers require two data bytes. Reading the LM77 can take place either of two ways: If the location latched in the Pointer is correct (most of the time it is expected that the Pointer will point to the Temperature register because it will be the data most frequently read from the LM77), then the read can simply consist of an address byte, followed by retrieving the corresponding number of data bytes. If the Pointer needs to be set, then an address byte, pointer byte, repeat start, and another address byte plus required number of data bytes will accomplish a read. 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 the temperature condition. For instance, if the first four bits of the temperature data indicates a critical condition, the host processor could immediately take action to remedy the excessive temperature. At the end of a read, the LM77 can accept either Acknowledge or No Acknowledge from the Master (No Acknowledge is typically used as a signal for the slave that the Master has read its last byte). An inadvertent 8-bit read from a 16-bit register, with the D7 bit low, can cause the LM77 to stop in a state where the SDA line is held low as shown in Figure 4. This can prevent any further bus communication until at least 9 additional clock cycles have occurred. Alternatively, the master can issue clock cycles until SDA goes high, at which time issuing a “Stop” condition will reset the LM77. DS100136-8 FIGURE 4. Inadvertent 8-Bit Read from 16-Bit Register where D7 is Zero (“0”) www.national.com 10 LM77 1.0 Functional Description 1.9 POINTER REGISTER (Continued) (Selects which registers will be read from or written to): P7 0 P0–P2: Register Select: P2 0 0 0 0 1 1 P3–P7: Must be kept zero. 1.10 TEMPERATURE REGISTER (Read Only): D15 Sign D14 Sign D13 Sign D12 Sign D11 MSB D10 Bit 7 D9 Bit 6 D8 Bit 5 D7 Bit 4 D6 Bit 3 D5 Bit 2 D4 Bit 1 D3 Bit 0 D2 CRIT P6 0 P5 0 P4 0 P3 0 P2 P1 P0 Register Select P1 0 0 1 1 0 0 P0 0 1 0 1 0 1 Register Temperature (Read only) (Power-up default) Configuration (Read/Write) THYST (Read/Write) T_CRIT (Read/Write) TLOW (Read/Write) THIGH (Read/Write) D1 HIGH D0 LOW Status Bits D0–D2: Status Bits D3–D15: Temperature Data. One LSB = 0.5˚C. Two’s complement format. 1.11 CONFIGURATION REGISTER (Read/Write): D7 0 D6 0 D5 0 D4 Fault Queue D3 INT Polarity D2 T_CRIT_A Polarity D1 INT Mode D0 Shutdown D0: Shutdown - When set to 1 the LM77 goes to low power shutdown mode. Power up default of “0”. D1: Interrupt mode - 0 is Comparator Interrupt mode, 1 is Event Interrupt mode. Power up default of “0”. D2, D3: T_CRIT_A and INT Polarity - 0 is active low, 1 is active high. Outputs are open-drain. Power up default of “0” D4: Fault Queue - When set to 1 the Fault Queu is enabled, see Section 1.7. Power up default of “0”. D5–D7: These bits are used for production testing and must be kept zero for normal operation. 1.12 THYST, TLOW, THIGH AND T_CRIT_A REGISTERS (Read/Write): D15 Sign D14 Sign D13 Sign D12 Sign D11 MSB D10 Bit7 D9 Bit6 D8 Bit5 D7 Bit 4 D6 Bit 3 D5 Bit 2 D4 Bit 1 D3 Bit 0 D2 X D1 X D0 X D0–D2: Undefined D3–D15: THYST, TLOW, THIGH or T_CRIT Trip Temperature Data. Power up default is TLOW = 10˚C, THIGH = 64˚C, T_CRIT = 80˚C, THYST = 2˚C. THYST is subtracted from THIGH, and T_CRIT, and added to TLOW. Avoid programming setpoints so close that their hysteresis values overlap. See Section 1.1. 11 www.national.com LM77 2.0 I2C Timing Diagrams DS100136-9 Typical 2-Byte Read From Preset Pointer Location Such as Temp or Comparison Registers DS100136-10 Typical Pointer Set Followed by Immediate Read for 2-Byte Register such as Temp or Comparison Registers DS100136-11 Typical 1-Byte Read from Configuration Register with Preset Pointer DS100136-12 Typical Pointer Set Followed by Immediate Read from Configuration Register DS100136-13 Configuration Register Write DS100136-14 Comparison Register Write FIGURE 6. Timing Diagrams www.national.com 12 LM77 3.0 Application Hints The temperature response graph in Figure 7 depicts a typical application designed to meet ACPI requirements. In this type of application, the temperature scale is given an arbitrary value of ″granularity″, or the window within which temperature notification events should occur. The LM77 can be programmed to the window size chosen by the designer, and will issue interrupts to the processor whenever the window limits have been crossed. The internal flags permit quick determination of whether the temperature is rising or falling. The T_CRIT limit would typically use its separate output to activate hardware shutdown circuitry separate from the processor. This is done because it is expected that if temperature has gotten this high that the processor may not be responding. The separate circuitry can then shut down the system, usually by shutting down the power supply. Note that the INT and T_CRIT_A outputs are separate, but can be wire-or’d together. Alternatively the T_CRIT_A can be diode or’d to the INT line in such a way that a T_CRIT_A event activates the INT line, but an INT event does not activate the T_CRIT_A line. This may be useful in the event that it is desirable to notify both the processor and separate T_CRIT_A shutdown circuitry of a critical temperature alarm at the same time (maybe the processor is still working and can coordinate a graceful shutdown with the separate shutdown circuit). To implement ACPI compatible sensing it is necessary to sense whenever the temperature goes outside the window, issue an interrupt, service the interrupt, and reprogram the window according to the desired granularity of the temperature scale. The reprogrammed window will now have the current temperature inside it, ready to issue an interrupt whenever the temperature deviates from the current window. To understand this graph, assume that at the left hand side the system is at some nominal temperature. For the 1st event temperature rises above the upper window limit, THIGH, causing INT to go active. The system responds to the interrupt by querying the LM77’s status bits and determines that THIGH was exceeded, indicating that temperature is rising. The system then reprograms the temperature limits to a value higher by an amount equal to the desired granularity. Note that in Event Interrupt Mode, reprogramming the limits has caused a second, known, interrupt to be issued since temperature has been returned within the window. In Comparator Interrupt Mode, the LM77 simply stops issuing interrupts. The 2nd event is another identical rise in temperature. The 3rd event is typical of a drop in temperature. This is one of the conditions that demonstrates the power of the LM77, as the user receives notification that a lower limit is exceeded in such a way that temperature is dropping. The Critical Alarm Event activates the separate T_CRIT_A output. Typically, this would feed circuitry separate from the processor on the assumption that if the system reached this temperature, the processor might not be responding. 13 www.national.com LM77 3.0 Application Hints (Continued) DS100136-15 Note: Event Interrupt mode is drawn as if the user is reading the part. If the user doesn’t read, the outputs would go low and stay that way until the LM77 is read. FIGURE 7. Temperature Response Diagram for ACPI Implementation 4.0 Typical Applications DS100136-16 FIGURE 8. Typical Application www.national.com 14 LM77 4.0 Typical Applications (Continued) DS100136-17 FIGURE 9. Remote HVAC temperature sensor communicates via 3 wires, including thermostat signals. DS100136-19 FIGURE 10. ACPI Compatible Terminal Alarm Shutdown. By powering the LM77 from auxilary output of the power supply, a non-functioning overheated computer can be powered down to preserve as much of the system as possible. 15 www.national.com LM77 Physical Dimensions inches (millimeters) unless otherwise noted 8-Lead (0.150" Wide) Molded Small Outline Package (SOP), JEDEC Registration Number MS-012 (variation AA), Order Number LM77CIM-3, LM77CIMX-3, LM77CIM-5 or LM77CIMX-5 NS Package Number M08A www.national.com 16 LM77 9-Bit + Sign Digital Temperature Sensor and Thermal Window Comparator with Two-Wire Interface Physical Dimensions inches (millimeters) unless otherwise noted (Continued) 8-Lead (0.150" Wide) Molded Mini Small Outline Package (MSOP), JEDEC Registration Number MO-187 (variation AA), Order Number LM77CIMM-3, LM77CIMMX-3, LM77CIMM-5 or LM77CIMMX-5 NS Package Number MUA08A 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 Email: support@nsc.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 Français 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 www.national.com 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.