Page 1
January 2000
LM82
Remote Diode and Local Digital Temperature Sensor
with Two-Wire Interface
LM82 Remote Diode and Local Digital Temperature Sensor with Two-Wire Interface
General Description
The LM82 is a digital temperature sensor with a 2 wire serial
interface thatsensesthe voltage and thus the temperature of
a remote diode using a Delta-Sigma analog-to-digital converter with a digital over-temperature detector.The LM82 accurately senses its own temperature as well as the temperature of external devices, such as Pentium II
diode connected 2N3904s. The temperature of any ASIC
can be detected using the LM82 as long as a dedicated diode (semiconductor junction) is available on the die. Using
the SMBus interface a host can access the LM82’sregisters
at any time. Activation of a T_CRIT_A output occurs when
any temperature is greater than a programmable comparator
limit, T_CRIT. Activation of an INT output occurs when any
temperature is greater than its corresponding programmable
comparator HIGH limit.
The host can program as well as read back the state of the
T_CRIT register and the 2 T_HIGH registers. Three state
logic inputs allow two pins (ADD0, ADD1) to select up to 9
SMBus address locations for the LM82. The sensor powers
up with default thresholds of 127˚C for T_CRIT and all
T_HIGHs. The LM82 is pin for pin and register compatible
with the LM84, Maxim MAX1617 and Analog Devices
ADM1021.
®
Processors or
Features
n Accurately senses die temperature of remote ICs, or
diode junctions
n On-board local temperature sensing
n SMBus and I
SMBus 1.1 TIMEOUT
n Two interrupt outputs: INT and T_CRIT_A
n Register readback capability
n 7 bit plus sign temperature data format, 1 ˚C resolution
n 2 address select pins allow connection of 9 LM82s on a
single bus
2
C compatible interface, supports
Key Specifications
j
Supply Voltage 3.0V to 3.6V
j
Supply Current 0.8mA (max)
j
Local Temp Accuracy (includes quantization error)
0˚C to +85˚C
j
Remote Diode Temp Accuracy (includes quantization
error)
+25˚C to +100˚C
0˚C to +125˚C
±
3.0˚C (max)
±
3˚C (max)
±
4˚C (max)
Applications
n System Thermal Management
n Computers
n Electronic Test Equipment
n Office Electronics
n HVAC
Simplified Block Diagram
DS101297-1
SMBus™is a trademark of the Intel Corporation.
®
Pentium II
is a registered trademark of the Intel Corporation.
®
I2C
is a registered trademark of the Philips Corporation.
© 2000 National Semiconductor Corporation DS101297 www.national.com
Page 2
Connection Diagram Ordering Information
LM82
QSOP-16
DS101297-2
TOP VIEW
Order
Number
LM82CIMQA
LM82CIMQAX
Typical Application
NS
Package
Number
MQA16A
(QSOP-16)
MQA16A
(QSOP-16)
Transport
Media
95 Units in
Rail
2500 Units on
Tape and
Reel
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DS101297-3
Page 3
Pin Description
LM82
Label Pin
#
Function Typical Connection
floating, unconnected Left floating. PC board traces may be routed
NC 1, 5
V
CC
2
Positive Supply Voltage
Input
Diode Current Source To Diode Anode. Connected to remote discrete
D+ 3
D− 4
ADD0–ADD1 10, 6
Diode Return Current
Sink
User-Set SMBus (I
2
Address Inputs
C)
GND 7, 8 Power Supply Ground Ground
Manufacturing test pins. Left floating. PC board traces may be routed
NC 9, 13, 15
INT
11
SMBData 12
Interrupt Output,
open-drain
SMBus (I
2
C) Serial
Bi-Directional Data Line,
open-drain output
2
SMBCLK 14 SMBus (I
T_CRIT_A
16
Critical Temperature
Alarm, open-drain output
C) Clock Input From Controller, Pull-Up Resistor
through the pads for these pins. No restrictions
applied.
DC Voltage from 3.0 V to 3.6 V
diode junction or to the diode junction on a remote
IC whose die temperature is being sensed. When
not used they should be left floating.
To Diode Cathode. Must float when not used.
Ground (Low, “0”), VCC(High, “1”) or open
(“TRI-LEVEL”)
through the pads for these pins, although the
components that drive these traces should share
the same supply as the LM82 so that the Absolute
Maximum Rating, Voltage at Any Pin, is not
violated.
Pull Up Resistor, Controller Interrupt or Alert Line
From and to Controller, Pull-Up Resistor
Pull Up Resistor, Controller Interrupt Line or
System Shutdown
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Page 4
Absolute Maximum Ratings (Note 1)
LM82
Supply Voltage −0.3 V to 6.0 V
Voltage at SMBData,
SMBCLK, T_CRIT_A & INT pins
Voltage at Other Pins −0.3 V to
D− Input Current
Input Current at All Other Pins (Note
2) 5 mA
Package Input Current (Note 2) 20 mA
SMBData, T_CRIT_A, INT Output
Sink Current 10 mA
Storage Temperature −65˚C to +150˚C
−0.5V to 6V
+ 0.3 V)
(V
CC
±
1mA
QSOP Package (Note 3)
Vapor Phase (60 seconds) 215˚C
Infrared (15 seconds) 220˚C
ESD Susceptibility (Note 4)
Human Body Model 2000 V
Machine Model 250 V
Operating Ratings
(Notes 1, 5)
Specified Temperature Range T
LM82 −40˚C to +125˚C
Supply Voltage Range (V
) +3.0V to +3.6V
CC
Soldering Information, Lead Temperature
Temperature-to-Digital Converter Characteristics
Unless otherwise noted, these specifications apply for VCC=+3.0 Vdc to 3.6 Vdc. Boldface limits apply for TA=TJ=T
to T
Temperature Error using Local
Diode ((Note 8))
Temperature Error using Remote
Diode ((Note 8))
Resolution 8 Bits
Conversion Time of All
Temperatures
Quiescent Current (Note 9) SMBus (I
D− Source Voltage 0.7 V
Diode Source Current (D+ − D−)=+ 0.65V; high
T_CRIT_A and INT Output
Saturation Voltage
Power-On Reset Threshold On V
Local and Remote T_CRIT and
HIGH Default Temperature settings
; all other limits TA=TJ=+25˚C, unless otherwise noted.
MAX
Parameter Conditions Typical Limits Units
(Note 6) (Note 7) (Limit)
T
= 0 ˚C to +85˚C,
A
=+3.3V
V
CC
T
= −40 ˚C to +125˚C,
A
=+3.3V
V
CC
T
= +60 ˚C to +100˚C,
A
=+3.3V
V
CC
T
= 0 ˚C to +100˚C,
A
=+3.3V
V
CC
T
= 0 ˚C to +125˚C,
A
=+3.3V
V
CC
±
1
±
3 ˚C (max)
±
4 ˚C (max)
±
3
±
3 ˚C (max)
±
4 ˚C (max)
1˚C
(Note 10) 460 600 ms (max)
2
C) Inactive 0.500 0.80 mA (max)
125 µA (max)
level
60 µA (min)
Low level 15 µA (max)
5 µA (min)
I
= 3.0 mA 0.4
OUT
edge
input, falling
CC
2.3
1.8
(Note 11) +127 ˚C
to T
MIN
˚C (max)
V (max)
V (max)
V (min)
MAX
MIN
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Page 5
Logic Electrical Characteristics
DIGITAL DC CHARACTERISTICS
Unless otherwise noted, these specifications apply for VCC=+3.0 to 3.6 Vdc. Boldface limits apply for TA=TJ=T
T
; all other limits TA=TJ=+25˚C, unless otherwise noted.
MAX
Symbol Parameter Conditions Typical Limits Units
(Note 6) (Note 7) (Limit)
SMBData, SMBCLK
V
V
IN(1)
IN(0)
V
IN(HYST)
Logical “1” Input Voltage 2.1 V (min)
Logical “0”Input Voltage 0.8 V (max)
SMBData and SMBCLK Digital
300 mV
Input Hysteresis
I
I
IN(1)
IN(0)
Logical “1” Input Current VIN=V
CC
0.005 1.5 µA (max)
Logical “0” Input Current VIN= 0 V −0.005 1.5 µA (max)
ADD0, ADD1
V
V
I
I
IN(1)
IN(0)
IN(1)
IN(0)
Logical “1” Input Voltage V
CC
1.5 V (min)
Logical “0”Input Voltage GND 0.6 V (max)
Logical “1” Input Current VIN=V
CC
2 µA (max)
Logical “0” Input Current VIN=0V -2 µA (max)
ALL DIGITAL INPUTS
C
IN
Input Capacitance 20 pF
ALL DIGITAL OUTPUTS
I
OH
V
OL
High Level Output Current VOH=V
SMBus Low Level Output
Voltage
IOL=3mA
=6mA
I
OL
CC
100 µA (max)
0.4
0.6
MIN
V (max)
LM82
to
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Page 6
Logic Electrical Characteristics (Continued)
LM82
SMBus DIGITAL SWITCHING CHARACTERISTICS
Unless otherwise noted, these specifications apply for VCC=+3.0 Vdc to +3.6 Vdc, CL(load capacitance) on output lines = 80
pF. Boldface limits apply for T
The switching characteristics of the LM82 fully meet or exceed the published specifications of the SMBus or I2C bus. The following parameters are the timing relationships between SMBCLK and SMBData signals related to the LM82. They are not the
2
I
C or SMBus bus specifications.
A=TJ=TMIN
to T
; all other limits TA=TJ= +25˚C, unless otherwise noted.
MAX
Symbol Parameter Conditions Typical Limits Units
(Note 6) (Note 7) (Limit)
f
SMB
SMBus Clock Frequency 100
10
t
LOW
SMBus Clock Low Time 10 % to 10 % 1.3
25
t
MEXT Cumulative Clock Low Extend Time 10 ms (max)
LOW
t
HIGH
t
R,SMB
t
F,SMB
t
OF
t
TIMEOUT
t
1
t
,
2
t
SU;DAT
t
,
3
t
HD;DAT
t
,
4
t
HD;STA
t
,
5
t
SU;STO
t
,
6
t
SU;STA
t
BUF
SMBus Clock High Time 90 % to 90% 0.6 µs (min)
SMBus Rise Time 10% to 90% 1 µs (max)
SMBus Fall Time 90% to 10% 0.3 ns (max)
Output Fall Time CL= 400 pF,
=3mA
I
O
SMBData and SMBCLK Time Low for
Reset of Serial Interface (Note 12)
250 ns (max)
25
40
SMBCLK (Clock) Period 10 µs (min)
Data In Setup Time to SMBCLK High 100 ns (min)
Data Out Stable after SMBCLK Low 300
TBD
SMBData Low Setup Time to SMBCLK
100 ns (min)
Low
SMBData High Delay Time after
100 ns (min)
SMBCLK High (Stop Condition Setup)
SMBus Start-Condition Setup Time 0.6 µs (min)
SMBus Free Time 1.3 µs (min)
kHz (max)
kHz (min)
µs (min)
ms (max)
ms (min)
ms (max)
ns (min)
ns (max)
SMBus Communication
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DS101297-4
Page 7
Logic Electrical Characteristics (Continued)
SMBus TIMEOUT
DS101297-7
See drawing DS10129707
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 (V
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.
Parasitic components and or ESD protection circuitry are shown in the figure below for the LM82’s pins. The nominal breakdown voltage of the zener D3 is 6.5 V.
Care should be taken not to forward bias the parasitic diode, D1, present on pins: D+, D−,ADD1 andADD0. Doing so by more than 50 mV may corrupt a temperature
or voltage measurement.
) at any pin exceeds the power supplies (V
I
<
GND or V
I
>
VCC), the current at that pin should be limited to 5 mA. The 20 mA
I
LM82
Pin Name D1 D2 D3 D4 Pin Name D1 D2 D3 D4
NC (pins1&5) T_CRIT_A & INT
V
CC
x SMBData x x
x
D+ x x x NC (pins9&15) x x x
D− xxxx SMBCLK x x
ADD0, ADD1 x x x NC (pin 13) x x
Note: An x indicates that the diode exists.
DS101297-13
FIGURE 1. ESD Protection Input Structure
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 Semicon-
ductor 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: Thermal resistance of the QSOP-16 package is 130˚C/W, junction-to-ambient when attached to a FR-4 printed circuit board with 1 oz. foil as shown in
.
ure 3
Fig-
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Page 8
Logic Electrical Characteristics (Continued)
LM82
Note 6: Typicals are at TA= 25˚C and represent most likely parametric norm.
Note 7: Limits are guaranteed to National’s AOQL (Average Outgoing Quality Level).
Note 8: The Temperature Error will vary less than
Note 9: Quiescent current will not increase substantially with an active SMBus.
Note 10: This specification is provided only to indicate how often temperature data is updated. The LM82 can be read at any time without regard to conversion state
(and will yield last conversion result).
Note 11: Default values set at power up.
Note 12: Holding the SMBData and/or SMBCLK lines Low for a time interval greater than t
state of an SMBus communication (SMBCLK and SMBData set High).
±
1.0˚C for a variation in VCCof 3V to 3.6V from the nominal of 3.3V.
will cause the LM82 to reset SMBData and SMBCLK to the IDLE
TIMEOUT
FIGURE 2. Temperature-to-Digital Transfer Function (Non-linear scale for clarity)
FIGURE 3. Printed Circuit Board Used for Thermal Resistance Specifications
1.0 Functional Description
The LM82 temperature sensor incorporates a band-gap type
temperature sensor using a Local or Remote diode and an
8-bit ADC (Delta-Sigma Analog-to-Digital Converter). The
LM82 is compatible with the serial SMBus and I
interfaces. Digital comparators compare Local (LT) and Remote (RT) temperature readings to user-programmable setpoints (LHS, RHS, and TCS).Activation of the INT output indicates that a comparison is greater than the limit preset in a
HIGH register. The T_CRIT setpoint (TCS) interacts with all
the temperature readings. Activation of the T_CRIT_A output
indicates that any or all of the temperature readings have exceed the T_CRIT setpoint.
1.1 CONVERSION SEQUENCE
The LM82 converts its own temperature as well as a remote
diode temperature in the following sequence:
1. Local Temperature (LT)
2. Remote Diode (RT)
2
C two wire
DS101297-5
DS101297-24
This round robin sequence takes approximately 480 ms to
complete.
1.2 INT OUTPUT and T_HIGH LIMITS
Each temperature reading (LT, and RT) is associated with a
T_HIGH setpoint register (LHS, RHS). At the end of a temperature reading a digital comparison determines whether
that reading has exceeded its HIGH setpoint. If the temperature reading is greater than the HIGH setpoint, a bit is set in
one of the Status Registers, to indicate which temperature
reading, and the INT output is activated.
Local and remote temperature diodes are sampled in sequence by the A/D converter. The INT output and the Status
Register flags are updated at the completion of a conversion,
which occurs approximately 60 ms after a temperature diode
is sampled. INT is deactivated when the Status Register,
containing the set bit, is read and a temperature reading is
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Page 9
1.0 Functional Description (Continued)
less than or equal to it’s corresponding HIGH setpoint, as
shown in
for the INT output and related circuitry.
*
Note: Status Register Bits are reset by a read of Status Register where
bit is located.
Figure 4.Figure 5
shows a simplified logic diagram
DS101297-14
FIGURE 4. INT Temperature Response Diagram
conversion is below the T_CRIT setpoint, as shown in
6
.
Figure 7
shows a simplified logic diagram of the
Figure
T_CRIT_A and related circuitry.
DS101297-6
*
Note: Status Register Bits are reset by a read of Status Register where
bit is located.
FIGURE 6. T_CRIT_A Temperature Response Diagram
LM82
DS101297-21
FIGURE 5. INT output related circuitry logic diagram
The INT output can be disabled by setting the INT mask bit,
D7, of the configuration register. INT can be programmed to
be active high or low by the state of the INT inversion bit, D1,
in the configuration register. A “0” would program INT to be
active low. INT is an open-drain output.
1.3 T_CRIT_A OUTPUT and T_CRIT LIMIT
T_CRIT_A is activated when any temperature reading is
greater than the limit preset in the critical temperature setpoint register (T_CRIT), as shown in
Figure 6
. The Status
Registers can be read to determine which event caused the
alarm. A bit in the Status Registers is set high to indicate
which temperature reading exceeded the T_CRIT setpoint
temperature and caused the alarm, see
Section 2.3
.
Local and remote temperature diodes are sampled in sequence by the A/D converter. The T_CRIT_A output and the
Status Register flags are updated at the completion of a conversion. T_CRIT_A and the Status Register flags are reset
only after the Status Register is read and if a temperature
DS101297-20
FIGURE 7. T_CRIT_A output related circuitry logic
diagram
Located in the Configuration Register are the mask bits for
each temperature reading, see
Section 2.5
. When a mask bit
is set, its corresponding status flag will not propagate to the
T_CRIT_A output, but will still be set in the Status Registers.
Configuration register bits D5 and D3, labled “Remote
T_CRIT_A mask” must be set high before the T_CRIT setpoint is lowered in order for the T_CRIT_A output to function
properly. Setting all four mask bits or programming the
T_CRIT setpoint to 127˚C will disable the T_CRIT_A output.
1.4 POWER ON RESET DEFAULT STATES
LM82 always powers up to these known default states:
1. Command Register set to 00h
2. Local Temperature set to 0˚C
3. Remote Temperature set to 0˚C until the LM82 senses a
diode present between the D+ and D− input pins.
4. Status Register set to 00h.
5. Configuration Register set to 00h; INT enabled and all
T_CRIT setpoints enabled to activate T_CRIT_A.
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Page 10
1.0 Functional Description (Continued)
LM82
6. Local and Remote T_CRIT set to 127˚C
1.5 SMBus INTERFACE
The LM82 operates as a slave on the SMBus, so the
SMBCLK line is an input (no clock is generated by the LM82)
and the SMBData line is bi-directional. According to SMBus
specifications, the LM82 has a 7-bit slave address. Bit 4 (A3)
of the slave address is hard wired inside the LM82 to a 1.
The remainder of the address bits are controlled by the state
of the address select pins ADD1 and ADD0, and are set by
connecting these pins to ground for a low, (0) , to V
high, (1), or left floating (TRI-LEVEL).
Therefore, the complete slave address is:
A6 A5 A4 1 A2 A1 A0
MSB LSB
and is selected as follows:
Address Select Pin State LM82 SMBus
Slave Address
ADD0 ADD1 A6:A0 binary
0 0 001 1000
0 TRI-LEVEL 001 1001
0 1 001 1010
TRI-LEVEL 0 010 1001
TRI-LEVEL TRI-LEVEL 010 1010
TRI-LEVEL 1 010 1011
1 0 100 1100
1 TRI-LEVEL 100 1101
1 1 100 1110
The LM82 latches the state of the address select pins during
the first read or write on the SMBus. Changing the state of
the address select pins after the first read or write to any device on the SMBus will not change the slave address of the
LM82.
Temperature Digital Output
Binary Hex
+125˚C 0111 1101 7Dh
+25˚C 0001 1001 19h
+1˚C 0000 0001 01h
0˚C 0000 0000 00h
−1˚C 1111 1111 FFh
−25˚C 1110 0111 E7h
−55˚C 1100 1001 C9h
for a
CC
1.7 OPEN-DRAIN OUTPUTS
The SMBData, 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 internal temperature reading
errors due to internal heating of the LM82. The maximum resistance of the pull up, based on LM82 specification for High
Level Output Current, to provide a 2.1V high level, is 30kΩ.
Care should be taken in a noisy system because a high impedance pull-up will be more likely to couple noise into the
signal line.
1.8 DIODE FAULT DETECTION
Before each external conversion the LM82 goes through an
external diode fault detection sequence. If D+ input is
shorted to V
be +127 ˚C, and the OPEN bit in the Status Register will be
set. If the T_CRIT setpoint is set to less than +127 ˚C then
the D+ input RTCRIT bit in the Status Register will be set
which will activate the T_CRIT_A output, if enabled. If a D+
is shorted to GND or D−, its temperature reading will be 0 ˚C
and its OPEN bit in the Status Register will not be set.
or floating then the temperature reading will
CC
1.6 TEMPERATURE DATA FORMAT
Temperature data can be read from the Local and Remote
Temperature, T_CRIT, and HIGH setpoint registers; and written to the T_CRIT and HIGH setpoint registers. Temperature
data is represented by an 8-bit, two’s complement byte with
an LSB (Least Significant Bit) equal to 1˚C:
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Page 11
1.0 Functional Description (Continued)
1.9 COMMUNICATING with the LM82
LM82
There are 13 data registers in the LM82, selected by the
Command Register. At power-up the Command Register is
set to “00”, the location for the Read LocalTemperatureRegister. The Command Register latches the last location it was
set to. Reading the Status Register resets T_CRIT_A and
INT, so long as a temperature comparison does not signal a
fault (see
Sections 1.2 and 1.3
). All other registers are predefined as read only or write only. Read and write registers
with the same function contain mirrored data.
AWrite to the LM82 will always include the address byte and
the command byte. A write to any register requires one data
byte.
Reading the LM82 can take place either of two ways:
1. If the location latched in the Command Register is cor-
rect (most of the time it is expected that the Command
Register will point to one of the Read Temperature Registers because that will be the data most frequentlyread
from the LM82), then the read can simply consist of an
address byte, followed by retrieving the data byte.
2. If the Command Register needs to be set, then an ad-
dress byte, command byte, repeat start, and another address byte will accomplish a read.
The data byte has the most significant bit first. At the end of
a read, the LM82 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).
DS101297-9
1.10 SERIAL INTERFACE ERROR RECOVERY
The LM82 SMBus lines will be reset to the SMBus idle state
if the SMBData or SMBCLK lines are held low for 40 ms or
more (t
). The LM82 may or may not reset the state of
TIMEOUT
the serial interface logic if either of the SMBData or SMBCLK
lines are held low between 25 ms and 40 ms. TIMEOUT allows a clean recovery in cases where the master may be reset while the LM82 is transmitting a low bit thus preventing
possible bus lock up.
Whenever the LM82 sees the start condition its serial interface will reset to the beginning of the communication, thus
the LM82 will expect to see an address byte next. This simplifies recovery when the master is reset while the LM82 is
transmitting a high.
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Page 12
1.0 Functional Description (Continued)
LM82
2.0 LM82 REGISTERS
2.1 COMMAND REGISTER
Selects which registers will be read from or written to. Data for this register should be transmitted during the Command Byte of
the SMBus write communication.
P7 P6 P5 P4 P3 P2 P1 P0
0 Command Select
P0-P7: Command Select
Command Se-
lect Address
<
P7:P0>hex
00h 0000 0000 0 RLT Read Local Temperature
01h 0000 0000 0 RRT Read Remote Temperature
02h 0000 0000 0 RSR Read Status Register
03h 0000 0000 0 RC Read Configuration
04h 0000 0000 0 Reserved
05h 0111 1111 127 RLHS Read Local HIGH Setpoint
06h Reserved
07h 0111 1111 127 RRHS Read Remote HIGH Setpoint
08h Reserved
09h 0000 0000 WC Write Configuration
0Ah Reserved
0Bh 0111 1111 127 WRHS Write Local HIGH Setpoint
0Ch Reserved
0Dh 0111 1111 127 WLHS Write Local HIGH Setpoint
0Eh-2Fh Reserved for Future Use
30h-31h 0000 0000 0 Reserved
32h-34h Reserved for Future Use
35h 0000 0000 0 Reserved
36h-37h Reserved for Future Use
38h 0111 1111 127 Reserved
39h Reserved for Future Use
3Ah 0111 1111 127 Reserved
3Bh-41h Reserved for Future Use
42h 0111 1111 127 RTCS Read T_CRIT Setpoint
43h-4Fh Reserved for Future Use
50h 0111 1111 127 Reserved
51h Reserved for Future Use
52h 0111 1111 127 Reserved
53h-59h Reserved for Future Use
5Ah 0111 1111 127 WTCS Write T_CRIT Setpoint
5Ch-6Fh and
F0h-FDh
FEh 0000 0001 1 RMID Read Manufacturers ID
FFh 1 RSR Read Stepping or Die
Power On Default State Register Name Register Function
<
D7:D0>binary<D7:D0>deci-
mal
Reserved for Future Use
Revision Code
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Page 13
1.0 Functional Description (Continued)
2.2 LOCAL and REMOTE TEMPERATURE REGISTERS (LT, and RT)
(Read Only Address 00h, and 01h):
D7 D6 D5 D4 D3 D2 D1 D0
MSB Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 LSB
D7–D0: Temperature Data. One LSB = 1˚C. Two’s complement format.
2.3 STATUS REGISTER
(Read Only Address 02h):
D7 D6 D5 D4 D3 D2 D1 D0
0 LHIGH 0 RHIGH 0 OPEN RCRIT LCRIT
Power up default is with all bits “0” (zero).
D0: LCRIT: When set to a 1 indicates an Local Critical Temperature alarm.
D1: RCRIT: When set to a 1 indicates a Remote Diode Critical Temperature alarm.
D2: D2OPEN: When set to 1 indicates a Remote Diode disconnect.
D4: D2RHIGH: When set to 1 indicates a Remote Diode HIGH Temperature alarm.
D6: LHIGH: When set to 1 indicates a Local HIGH Temperature alarm.
D7, D5, and D3: These bits are always set to 0 and reserved for future use.
2.4 MANUFACTURERS ID and DIE REVISION(Stepping)
REGISTERS
(Read Address FEh and FFh) Default value 01h for Manufacturers ID(FEh ).
LM82
2.5 CONFIGURATION REGISTER
(Read Address 03h/Write Address 09h):
D7 D6 D5 D4 D3 D2 D1 D0
INT mask
Power up default is with all bits “0” (zero).
D7: INT mask: When set to 1 INT interrupts are masked.
D5: T_CRIT mask, this bit must be set to a 1 before the T_CRIT setpoint is lowered below 127 in order for T_CRIT_A pin to func-
tion properly.
D4: T_CRIT mask for Remote temperature, when set to 1 a remote temperature reading that exceeds T_CRIT setpoint will not
activate the T_CRIT_A pin.
D3: T_CRIT mask, this bit must be set to a 1 before the T_CRIT setpoint is lowered below 127 in order for T_CRIT_A pin to func-
tion properly.
D2: T_CRIT mask for Local reading, when set to 1 a Local temperature reading that exceeds T_CRIT setpoint will not activate
the T_CRIT_A pin.
D1: INT active state inversion. When INT Inversion is set to a 1 the active state of the INT output will be a logical high. Alow would
then select an active state of a logical low.
D6 and D0: These bits are always set to 0 and reserved for future use. A write of 1 will return a 0 when read.
2.6 LOCAL, and REMOTE HIGH SETPOINT REGISTERS (LHS, RHS)
(Read Address 05h, 07h/Write Address 0Bh, 0Dh):
D7 D6 D5 D4 D3 D2 D1 D0
MSB Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 LSB
D7–D0: HIGH setpoint temperature data. Power up default is LHIGH = RHIGH=127˚C.
0 Remote
T_CRIT_A
mask
Remote
T_CRIT_A
mask
Remote
T_CRIT_A
mask
Local
T_CRIT_A
mask
INT Inversion
0
2.7 T_CRIT REGISTER (TCS)
(Read Address 42h/Write Address 5Ah):
D7 D6 D5 D4 D3 D2 D1 D0
MSB Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 LSB
D7–D0: T_CRIT setpoint temperature data. Power up default is T_CRIT = 127˚C.
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3.0 SMBus Timing Diagrams
LM82
(a) Serial Bus Write to the internal Command Register followed by a the Data Byte
DS101297-10
DS101297-11
(b) Serial Bus Write to the internal Command Register
DS101297-12
(c) Serial Bus Read from a Register with the internal Command Register preset to desired value.
FIGURE 8. Serial Bus Timing Diagrams
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Page 15
4.0 Application Hints
The LM82 can be applied easily in the same way as other
integrated-circuit temperature sensors and its remote diode
sensing capability allows it to be used in new ways as well.
It can be soldered to a printed circuit board, and because the
path of best thermal conductivity is between the die and the
pins, its temperature will effectively be that of the printed circuit board lands and traces soldered to the LM82’s pins. This
presumes that the ambient air temperature is almost the
same as the surface temperature of the printed circuit board;
if the air temperature is much higher or lower than the surface temperature, the actual temperature of the of the LM82
die will be at an intermediate temperature between the surface and air temperatures. Again, the primary thermal conduction path is through the leads, so the circuit board temperature will contribute to the die temperature much more
strongly than will the air temperature.
To measure temperature external to the LM82’s die, use a
remote diode. This diode can be located on the die of a target IC, allowing measurement of the IC’s temperature, independent of the LM82’s temperature. The LM82 has been optimized to measure the remote diode of a Pentium II
processor as shown in
used to sense the temperature of external objects or ambient
air.Remember that a discrete diode’s temperature will be affected, and often dominated, by the temperature of its leads.
Figure 9
.A discrete diode can also be
where:
η is the non-ideality factor of the process the diode is
•
manufactured on,
q is the electron charge,
•
k is the Boltzmann’s constant,
•
N is the current ratio,
•
T is the absolute temperature in ˚K.
•
The temperature sensor then measures ∆V
and converts
BE
to digital data. In this equation, k and q are well defined universal constants, and N is a parameter controlled by the temperature sensor. The only other parameter is η, which depends on the diode that is used for measurement. Since
∆V
is proportional to both η andT,the variations in η can-
BE
not be distinguished from variations in temperature. Since
the non-ideality factor is not controlled by the temperature
sensor,it will directly add to the inaccuracy of the sensor.For
the Pentium II Intel specifies a
±
1% variation in η from part
to part. As an example, assume a temperature sensor has
an accuracy specification of
±
3 ˚C at room temperature of 25
˚C and the process used to manufacture the diode has a
non-ideality variation of
±
1%. The resulting accuracy of the
temperature sensor at room temperature will be:
T
=±3˚C+(±1% of 298 ˚K) =±6 ˚C.
ACC
The additional inaccuracy in the temperature measurement
caused by η, can be eliminated if each temperature sensor is
calibrated with the remote diode that it will be paired with.
LM82
DS101297-15
Pentium or 3904 Temperature vs LM82 Temperature
Reading
Most silicon diodes do not lend themselves well to this application. It is recommended that a 2N3904 transistor base
emitter junction be used with the collector tied to the base.
A diode connected 2N3904 approximates the junction available on a Pentium microprocessor for temperature measurement. Therefore, the LM82 can sense the temperature of this
diode effectively.
3.1 ACCURACY EFFECTS OF DIODE NON-IDEALITY
FACTOR
The technique used in today’s remote temperature sensors
is to measure the change in V
at two different operating
BE
points of a diode. For a bias current ratio of N:1, this difference is given as:
3.2 PCB LAYOUT for MINIMIZING NOISE
In a noisy environment, such as a processor mother board,
layout considerations are very critical. Noise induced on
traces running between the remote temperature diode sensor and the LM82 can cause temperature conversion errors.
The following guidelines should be followed:
1. Place a 0.1 µF power supply bypass capacitor as close
as possible to the V
pin and the recommended 2.2 nF
CC
capacitor as close as possible to the D+ and D− pins.
Make sure the traces to the 2.2nF capacitor are
matched.
2. The recommended 2.2nF diode bypass capacitor actu-
ally has a range of 200pF to 3.3nF. The average temperature accuracy will not degrade. Increasing the capacitance will lower the corner frequency where
differential noise error affects the temperature reading
thus producing a reading that is more stable. Conversely, lowering the capacitance will increase the corner frequency where differential noise error affects the
temperature reading thus producing a reading that is
less stable.
3. Ideally, the LM82 should be placed within 10cm of the
Processor diode pins with the traces being as straight,
short and identical as possible. Trace resistance of 1Ω
can cause as much as 1˚C of error.
4. Diode traces should be surrounded by a GND guard ring
to either side, above and below if possible. This GND
guard should not be between the D+ and D− lines. In the
event that noise does couple to the diode lines it would
be ideal if it is coupled common mode. That is equally to
the D+ and D− lines.(See
Figure 10
)
5. Avoid routing diode traces in close proximity to power
supply switching signals or filtering inductors.
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Page 16
4.0 Application Hints (Continued)
LM82
6. Avoid running diode traces close to or parallel to high
speed digital and bus lines. Diode traces should bekept
at least 2cm. apart from the high speed digital traces.
7. If it is necessary to cross high speed digital traces, the
diode traces and the high speed digital traces should
cross at a 90 degree angle.
8. The ideal place to connect the LM82’s GND pin is as
close as possible to the Processors GND associated
with the sense diode.
9. Leakage current between D+ and GND should be kept
to a minimum. One nano-ampere of leakage can cause
as much as 1˚C of error in the diode temperature reading. Keeping the printed circuit board as clean as possible will minimize leakage current.
DS101297-17
FIGURE 10. Ideal Diode Trace Layout
Noise coupling into the digital lines greater than 300mVp-p
(typical hysteresis), overshoot greater than 500mV above
V
, and undershoot less than 500mV below GND, may pre-
CC
vent successful SMBus communication with the LM82. SMBus no acknowledge is the most common symptom, causing
unnecessary traffic on the bus. Although, the SMBus maximum frequency of communication is rather low (100kHz
max) care still needs to be taken to ensure proper termination within a system with multiple parts on the bus and long
printed circuit board traces. An R/C lowpass filter with a 3db
corner frequency of about 40MHz has been included on the
LM82’s SMBCLK input. Additional resistance can be added
in series with the SMBData and SMBCLK lines to further
help filter noise and ringing. Minimize noise coupling by
keeping digital traces out of switching power supply areas as
well as ensuring that digital lines containing high speeddata
communications cross at right angles to the SMBData and
SMBCLK lines.
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Page 17
Physical Dimensions inches (millimeters) unless otherwise noted
LM82 Remote Diode and Local Digital Temperature Sensor with Two-Wire Interface
16-Lead QSOP Package
Order Number LM82CIMQA or LM82CIMQAX
NS Package Number MQA16
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