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LM81

Serial Interface ACPI-Compatible Microprocessor System

Hardware Monitor

General Description

The LM81 is a highly integrated data acquisition system for

hardware monitoring of servers, Personal Computers, or

virtually any microprocessor-based system. In a PC, the

LM81 can be used to monitor power supply voltages, tem-

peratures, and fan speeds. Actual values for these inputs

can be read at any time. Programmable WATCHDOG limits

in the LM81 activate a fully programmable and maskable

interrupt system with two outputs (INT and T_CRIT_).

The LM81 has an on-chip digital output temperature sensor

with 9-bit or 12-bit resolution, a 6 analog input ADC with 8-bit

resolution and an 8-bit DAC. Two fan tachometer outputs

can be measured with the LM81’s FAN1 and FAN2 inputs.

The DAC, witha0to1.25V output voltage range, can be

used for fan speed control. Additional inputs are provided for

Chassis Intrusion detection circuits, and VID monitor inputs.

The LM81 has a Serial Bus interface that is compatible with

SMBus

™

Features

n Temperature sensing

n 6 positive voltage inputs with scaling resistors to monitor

+5V, +12V, +3.3V, +2.5V, Vccp power supplies directly

n 8-bit DAC output for controlling fan speed

n 2 fan speed monitoring inputs

n Chassis Intrusion detector input

n WATCHDOG comparison of all monitored values

n SMBus 1.0 (LM81C) and 1.1 (LM81B) Serial Bus

interface compatibility

n LM81B has improved voltage monitoring accuracy

n VID0-VID4 monitoring inputs

Key Specifications

Voltage Monitoring Error +2% or

1.2% (max)

Temperature Error

−40˚C to +125˚C

3˚C (max)

Supply Voltage Range 2.8V to 3.8V

Supply Current 0.4 mA (typ)

ADC and DAC Resolution 8 Bits

Temperature Resolution 0.5˚C

Applications

n System Thermal and Hardware Monitoring for Servers

and PCs

n Office Electronics

n Electronic Test Equipment and Instrumentation

Typical Application

DS100072-1

Indicates Active Low (“Not”)

February 2002

LM81 Serial Interface ACPI-Compatible Microprocessor System Hardware Monitor

Summary of content (33 pages)

PAGE 1
LM81 Serial Interface ACPI-Compatible Microprocessor System Hardware Monitor General Description The LM81 is a highly integrated data acquisition system for hardware monitoring of servers, Personal Computers, or virtually any microprocessor-based system. In a PC, the LM81 can be used to monitor power supply voltages, temperatures, and fan speeds. Actual values for these inputs can be read at any time.
PAGE 2
LM81 Ordering Information Temperature Range −40˚C ≤ TA ≤ +125˚C NS Package Number SMBus Revision Level Voltage Monitoring Error Order Number Device Marking LM81BIMT-31 LM81BIMT-3 MTC24B 1.1 LM81BIMTX-3 LM81BIMT-3 MTC24B 1.1 ± 1.2% ± 1.2% LM81CIMT-31 LM81CIMT-3 MTC24B 1.0 +2% LM81CIMTX-32 LM81CIMT-3 MTC24B 1.0 +2% 2 Note: 1-Rail transport media, 62 parts per rail 2 -Tape and reel transport media, 3400 parts per reel Connection Diagram DS100072-3 www.national.
PAGE 3
LM81 Block Diagram DS100072-2 Pin Description Pin Name(s) A0/NTEST_OUT Pin Number Number of Pins 1 1 Digital I/0 The lowest order programmable bit of the serial bus address. This pin functions as an output during NAND Tree tests (board-level connectivity testing). Refer to SECTION 11 on NAND Tree testing. Type Description A1 2 1 Digital Input The highest order programmable bit of the serial bus address. SMBData 3 1 Digital I/O Serial Bus bidirectional Data. Open-drain output.
PAGE 4
LM81 Pin Description Pin Name(s) (Continued) Pin Number Number of Pins Type Description INT 10 1 Digital Output Interrupt active low open-drain output. This output is enabled when Bit 1 in the Configuration Register is set to 1. The default state is disabled. DACOut/NTEST_IN 11 1 Analog Output/Digital Input 0V to +1.25V amplitude 8-bit DAC output. When forced high by an external voltage the NAND Tree Test mode is enabled which provides board-level connectivity testing. Refer to Section 11.
PAGE 5
Soldering Information MTC Package (Note 7) : Vapor Phase (60 seconds) Infrared (15 seconds) Storage Temperature If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/ Distributors for availability and specifications. Positive Supply Voltage (V+) Voltage on Any Input or Output Pin: +12Vin, T_CRIT_A A0, A1, DACOut +2.5Vin, +3.
PAGE 6
LM81 DC Electrical Characteristics (Continued) The following specifications apply for +2.8VDC ≤ V+ ≤ +3.8VDC, RS = 500Ω, unless otherwise specified. Boldface limits apply for TA = TJ = TMIN to TMAX; all other limits TA = TJ = 25˚C. (Note 8) Symbol Parameter Conditions Typical Limits LM81BIM Limits LM81CIM Units (Note 9) (Note 10) (Note 10) (Limits) ±5 ±5 ± 62.5 ± 10 ± 125 ± 62.5 DAC CHARACTERISTICS Resolution DAC Error 8 + V = 3.
PAGE 7
LM81 DC Electrical Characteristics (Continued) The following specifications apply for +2.8VDC ≤ V+ ≤ +3.8VDC, RS = 500Ω, unless otherwise specified. Boldface limits apply for TA = TJ = TMIN to TMAX; all other limits TA = TJ = 25˚C. (Note 8) Symbol Parameter Conditions Typical Limits LM81BIM Limits LM81CIM Units (Note 9) (Note 10) (Note 10) (Limits) DIGITAL OUTPUTS (NTEST_OUT) VOUT(1) Logical “1” Output Voltage IOUT = ± 3.0 mA at V+ = +2.8V 2.4 2.
PAGE 8
LM81 AC Electrical Characteristics The following specifications apply for +2.8VDC ≤ V+ ≤ +3.8VDC on SMBCLK and SMBData, unless otherwise specified. Boldface limits apply for TA = TJ = TMIN to TMAX; all other limits TA = TJ = 25˚C. (Note 15) Symbol Parameter Conditions Typical Limits Units (Note 9) (Note 10) (Limits) SERIAL BUS TIMING CHARACTERISTICS t1 2.
PAGE 9
LM81 AC Electrical Characteristics (Continued) Note 1: Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating Ratings indicate conditions for which the device is functional, but do not guarantee specific performance limits. For guaranteed specifications and test conditions, see the Electrical Characteristics. The guaranteed specifications apply only for the test conditions listed.
PAGE 10
LM81 Test Circuit DS100072-6 FIGURE 3. Digital Output Load Test Circuitry Functional Description • CI Clear Register: Allows transmitting a 20 ms low pulse on the chassis intrusion pin (CI). 1.0 GENERAL DESCRIPTION The LM81 provides 6 analog inputs, a temperature sensor, a Delta-Sigma ADC (Analog-to-Digital Converter), a DAC output, 2 fan speed counters, WATCHDOG registers, and a variety of inputs and outputs on a single chip. A two wire Serial Bus interface is included.
PAGE 11
purpose allows for the fastest possible response time to a thermal runaway event. This output can be enabled by setting bit 4 of Extended Mode Register 1. (Continued) Interrupt source. In addition, the Configuration Register has a control bit to enable or disable the hardware Interrupt. Another hardware Interrupt line available T_CRIT_A (Critical Temperature Alarm Output) is used to signal a catastrophic overtemperature event.
PAGE 12
LM81 Functional Description (Continued) 2.1 Internal Registers of the LM81 TABLE 1.
PAGE 13
LM81 Functional Description (Continued) 2.2 Serial Bus Interface DS100072-8 (a) Serial Bus Write to the Internal Address Register followed by the Data Byte DS100072-9 (b) Serial Bus Write to the Internal Address Register Only DS100072-10 (c) Serial Bus Read from a Register with the Internal Address Register Preset to Desired Location FIGURE 5. Serial Bus Timing Bus Interface Address byte, followed by the Internal Address Register byte.
PAGE 14
LM81 Functional Description Bit 0 of the Configuration Register controls the monitoring loop of the LM81. Setting Bit 0 low stops the LM81 monitoring loop and puts the LM81 in shutdown mode, reducing power consumption. Serial Bus communication can take place with any register in the LM81 although activity on the SMBData and SMBCLK lines will increase shutdown current, up to as much as maximum rated supply current, while the activity takes place.
PAGE 15
shown in the table below for the circuit of Figure 6 will provide approximately 1.25V at the Vccp analog inputs of the LM81 for a nominal reading of 89. (Continued) 3.5 Reading Conversion Results The conversion results are available in the Value RAM. Conversions can be read at any time and will provide the result of the last conversion. Because the ADC stops, and starts a new conversion whenever it is read, reads of any single value should not be done more often than once every 56 ms.
PAGE 16
LM81 Functional Description If fans can be powered while the power to the LM81 is off, the LM81 inputs will provide diode clamping. Limit input current to the Input Current at Any Pin specification shown in the ABSOLUTE MAXIMUM RATINGS section. In most cases, open collector outputs with pull-up resistors inherently limit this current. If this maximum current could be exceeded, either a larger pull up resistor should be used or resistors connected in series with the fan inputs.
PAGE 17
LM81 Functional Description (Continued) DS100072-12 (a) Fan with Tach Pull-Up to +5V DS100072-13 (b) Fan with Tach Pull-Up to +12V, or Totem-Pole Output and Resistor Attenuator DS100072-14 (c) Fan with Tach Pull-Up to +12V and Diode Clamp DS100072-15 (d) Fan with Strong Tach Pull-Up or Totem Pole Output and Diode Clamp FIGURE 7. Alternatives for Fan Inputs Counts are based on 2 pulses per revolution tachometer outputs. RPM Time per Revolution Counts for “Divide by 2” Comments 4400 13.
PAGE 18
LM81 Functional Description The output of the amplifier can be configured to provide a high or low side pass transistor. A high side pass transistor simplifies the coupling of tachometer outputs to the tachometer inputs of the LM81 since the fan remains grounded. Low side drive will require AC coupling along with clamping at the LM81 input to prevent negative excursions. (Continued) 7.0 DAC OUTPUT The LM81 provides an 8-bit DAC (Digital-to-Analog Converter) with an output range of 0 to 1.25 volts (4.
PAGE 19
8.1 Temperature Data Format (Continued) Temperature data can be read from the Temperature, THIGH setpoint, THIHYST setpoint, TLOW setpoint, TC setpoint and THYST Offset registers; and written to the THIGH setpoint, THIHYST, TLOW setpoint, T_CRIT setpoint and THYST offset registers. THIGH setpoint, TLOW setpoint, T_CRIT setpoint temperature data is represented by an 8-bit, two’s complement word with an LSB (Least Significant Bit) equal to 1˚C: 8.
PAGE 20
LM81 Functional Description Normal One-Time Interrupt Mode is shown in Figure 12 and operates in the following way: T_CRIT_A is disabled. Exceeding THIGH causes an interrupt that will remain active indefinitely until reset by reading Interrupt Status Register 1. Another interrupt will not occur until the temperature drops to less than or equal to THIHYST and then exceeds THIGH during a subsequent conversion. After power up this mode is selected as default. (Continued) 8.
PAGE 21
Extended Comparator Mode is shown in Figure 16 and operates in the following way: Interrupt is activated when the data from a temperature conversion is less than or equal to TLOW. Interrupt is reset when the data from a temperature conversion exceeds (TLOW + THIGH). Exceeding THIGH will activate interrupt. This interrupt will be reset when data from a temperature conversion is less than or equal to (THIGH − THYST). T_CRIT_A interrupt is activated when the temperature exceeds T_CRIT.
PAGE 22
LM81 Functional Description (Continued) 9.0 THE LM81 INTERRUPT STRUCTURE DS100072-22 FIGURE 17. Interrupt Structure Figure 17 depicts the Interrupt Structure of the LM81. The LM81 can generate Interrupts as a result of each of its internal WATCHDOG registers on the analog, temperature, and fan inputs. External Interrupts can come from the following source.
PAGE 23
ration Register high outputs a least 20 ms low on this line, at the end of which Bit 4 in the Configuration Register automatically clears. Again, the label for this pin is only its suggested use. In applications where the RESET capability is not needed it can be used for any type of digital control that requires a 20 ms active low open-drain output. (Continued) masks for each Interrupt. As described in Section 3.3, the hardware Interrupt line can also be enabled/disabled in the Configuration Register.
PAGE 24
LM81 Functional Description (Continued) 12.0 FAN MANUFACTURERS Manufacturers of cooling fans with tachometer outputs are listed below: NMB Tech 9730 Independence Ave. Chatsworth, California 91311 818 341-3355 818 341-8207 Model Number Frame Size Airflow CFM 2408NL 2.36 in sq. X 0.79 in 9-16 (60 mm sq. X 20 mm) 2410ML 2.36 in sq. X 0.98 in 14-25 (60 mm sq. X 25 mm) 3108NL 3.15 in sq. X 0.79 in 25-42 (80 mm sq. X 20 mm) 3110KL 3.15 in sq. X 0.98 in 25-40 (80 mm sq. X 25 mm) Mechatronics Inc.
PAGE 25
LM81 Functional Description (Continued) 13.0 REGISTERS AND RAM 13.1 Address Register The main register is the ADDRESS Register. The bit designations are as follows: Bit 7-0 Name Read/ Write Address Pointer Bit 7 Description Write Bit 6 Address of RAM and Registers. See the tables below for detail. Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0 A2 A1 A0 Address Pointer (Power On default 00h) A7 A6 A5 A4 A3 13.
PAGE 26
LM81 Functional Description (Continued) 13.3 Configuration Register — Address 40h Power on default – < 7:0 > = 00001000 binary Bit 0 Name Start Read/ Write Read/Write Description A one enables startup of monitoring operations, a zero puts the part in standby mode. Note: The outputs of Interrupt pins will not be cleared if the user writes a zero to this location after an interrupt has occurred unlike “INT_Clear” bit. At start up, limit checking functions and scanning begin.
PAGE 27
LM81 Functional Description (Continued) 13.4 Interrupt Status Register 1 — Address 41h Power on default – < 7:0 > = 0000 0000 binary Bit Name Read/Write Description 0 +2.5Vin Read Only A one indicates a High or Low limit has been exceeded. 1 Vccp1 Read Only A one indicates a High or Low limit has been exceeded. 2 +3.3Vin Read Only A one indicates a High or Low limit has been exceeded. 3 +5Vin Read Only A one indicates a High or Low limit has been exceeded.
PAGE 28
LM81 Functional Description (Continued) 13.7 Interrupt Mask Register 2 — Address 44h Power on default – < 7:0 > = 0000 0000 binary Bit Name Read/ Write Description 0 +12Vin Read/Write A one disables the corresponding interrupt status bit for INT interrupt. 1 Vccp2 Read/Write A one disables the corresponding interrupt status bit for INT interrupt.
PAGE 29
LM81 Functional Description (Continued) 13.10 VID/Fan Divisor Register — Address 47h Power on default – < 7:4 > is 0101, and < 3:0 > is mapped to VID < 3:0 > Bit Name 0-3 VID < 3:0 > Read/Write Read Only Description The VID < 3:0 > inputs from the Pentium/PRO power supplies that indicate the operating voltage (e.g. 1.5V to 2.9V). 4-5 FAN1 RPM Control Read/Write FAN1 Speed Control.
PAGE 30
LM81 Functional Description (Continued) 13.14 Extended Mode Register 1 — Address 4Ch Power on default – < 7:0 > = 0100 0100 binary Bit Name Read/Write Description 0 Extended Mode Enable Read/Write A one enables the Extended Interrupt Modes, the T_CRIT_A output and all the functions listed in the Extended Mode Registers. Bit 7 of the Interrupt Status register will be activated to reflect the interrupt status of the LOW limit comparison result.
PAGE 31
LM81 Functional Description (Continued) 13.16 Value RAM — Address 15h–3Fh Address A6–A0 Description 15h Manufacturers Test Register 19h DAC data register; power on default < 7:0 > =1111 1111 binary 20h +2.5Vin reading 21h Vccp1 reading 22h +3.3Vin reading 23h +5Vin reading 24h +12Vin reading 25h Vccp2 reading 26h Reserved reading 27h Temperature reading (8 MSBs) 28h FAN1 reading Note: This location stores the number of counts of the internal clock per revolution.
PAGE 32
LM81 Typical Application DS100072-23 FIGURE 19. In this PC application the LM81 monitors temperature, fan speed for 2 fans, and 6 power supply voltages. It also monitors an optical chassis intrusion detector. The LM81 provides a DAC output that can be used to control fan speed. www.national.
PAGE 33
inches (millimeters) unless otherwise noted 24-Lead TSSOP Order Number LM81BIMT-3, LM81BIMTX-3, LM81CIMT-3 or LM81CIMTX-3 NS Package Number MTC24B 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.