NSC LM82CIMQAX Remote diode and local digital temperature sensor with two-wire interface Datasheet

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 that senses the 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 ® Processors or 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’s
registers 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.
Features
n Accurately senses die temperature of remote ICs, or
diode junctions
n On-board local temperature sensing
n SMBus and I2C compatible interface, supports
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
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
± 3.0˚C (max)
j Remote Diode Temp Accuracy (includes quantization
error)
+25˚C to +100˚C
0˚C to +125˚C
± 3˚C (max)
± 4˚C (max)
Applications
n
n
n
n
n
System Thermal Management
Computers
Electronic Test Equipment
Office Electronics
HVAC
Simplified Block Diagram
10129701
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.
© 2004 National Semiconductor Corporation
DS101297
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LM82 Remote Diode and Local Digital Temperature Sensor with Two-Wire Interface
August 2004
LM82
Connection Diagram
QSOP-16
10129702
TOP VIEW
Ordering Information
Order
Number
NS Package
Number
Transport
Media
LM82CIMQA
MQA16A
(QSOP-16)
95 Units in
Rail
LM82CIMQAX
MQA16A
(QSOP-16)
2500 Units on
Tape and Reel
Typical Application
10129703
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2
LM82
Pin Descriptions
Label
Pin #
NC
1, 5
VCC
2
D+
3
D−
4
Function
Typical Connection
floating, unconnected
Left floating. PC board traces may be routed
through the pads for these pins. No restrictions
applied.
Positive Supply Voltage
Input
DC Voltage from 3.0 V to 3.6 V
Diode Current Source
To Diode Anode. Connected to remote discrete
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.
Diode Return Current Sink
To Diode Cathode. Must float when not used.
2
ADD0–ADD1
10, 6
User-Set SMBus (I C)
Address Inputs
Ground (Low, “0”), VCC (High, “1”) or open
(“TRI-LEVEL”)
GND
7, 8
Power Supply Ground
Ground
Manufacturing test pins.
Left floating. PC board traces may be routed
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.
NC
9, 13, 15
INT
11
Interrupt Output,
open-drain
Pull Up Resistor, Controller Interrupt or Alert Line
From and to Controller, Pull-Up Resistor
SMBData
12
SMBus (I2C) Serial
Bi-Directional Data Line,
open-drain output
SMBCLK
14
SMBus (I2C) Clock Input
From Controller, Pull-Up Resistor
16
Critical Temperature
Alarm, open-drain output
Pull Up Resistor, Controller Interrupt Line or System
Shutdown
T_CRIT_A
3
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LM82
Absolute Maximum Ratings (Note 1)
Supply Voltage
−0.3 V to 6.0 V
Voltage at SMBData,
SMBCLK, T_CRIT_A & INT pins
Vapor Phase (60 seconds)
215˚C
Infrared (15 seconds)
220˚C
ESD Susceptibility (Note 4)
−0.5V to 6V
Voltage at Other Pins
Human Body Model
−0.3 V to
(VCC + 0.3 V)
2000 V
Machine Model
250 V
± 1 mA
D− Input Current
Operating Ratings
Input Current at All Other Pins (Note
2)
5 mA
Package Input Current (Note 2)
(Notes 1, 5)
20 mA
SMBData, T_CRIT_A, INT Output
Sink Current
Storage Temperature
QSOP Package (Note 3)
Specified Temperature Range
LM82
10 mA
Supply Voltage Range (VCC)
−65˚C to +150˚C
TMIN to TMAX
−40˚C to +125˚C
+3.0V to +3.6V
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 = TMIN to
TMAX; all other limits TA= TJ=+25˚C, unless otherwise noted.
Parameter
Temperature Error using Local Diode
((Note 8))
Temperature Error using Remote
Diode ((Note 8))
Conditions
Typical
Limits
Units
(Note 6)
(Note 7)
(Limit)
±1
±3
˚C (max)
TA = −40 ˚C to +125˚C,
VCC=+3.3V
±4
˚C (max)
TA = +60 ˚C to +100˚C,
VCC=+3.3V
±3
TA = 0 ˚C to +100˚C,
VCC=+3.3V
±3
˚C (max)
TA = 0 ˚C to +125˚C,
VCC=+3.3V
±4
˚C (max)
TA = 0 ˚C to +85˚C,
VCC=+3.3V
Resolution
8
Bits
1
Conversion Time of All Temperatures
(Note 10)
Quiescent Current (Note 9)
SMBus (I2C) Inactive
˚C (max)
˚C
460
600
ms (max)
0.500
0.80
mA (max)
(D+ − D−)=+ 0.65V; high
level
125
µA (max)
60
µA (min)
Low level
15
µA (max)
5
µA (min)
T_CRIT_A and INT Output Saturation
Voltage
IOUT = 3.0 mA
0.4
Power-On Reset Threshold
On VCC input, falling edge
2.3
1.8
Local and Remote T_CRIT and HIGH
Default Temperature settings
(Note 11)
D− Source Voltage
Diode Source Current
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0.7
+127
4
V
V (max)
V (max)
V (min)
˚C
LM82
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 = TMIN to
TMAX; all other limits TA= TJ=+25˚C, unless otherwise noted.
Symbol
Parameter
Conditions
Typical
Limits
Units
(Note 6)
(Note 7)
(Limit)
SMBData, SMBCLK
VIN(1)
Logical “1” Input Voltage
2.1
V (min)
VIN(0)
Logical “0”Input Voltage
0.8
V (max)
VIN(HYST)
SMBData and SMBCLK Digital
Input Hysteresis
300
mV
IIN(1)
Logical “1” Input Current
VIN = VCC
0.005
1.5
µA (max)
IIN(0)
Logical “0” Input Current
VIN = 0 V
−0.005
1.5
µA (max)
ADD0, ADD1
VIN(1)
Logical “1” Input Voltage
VCC
1.5
V (min)
VIN(0)
Logical “0”Input Voltage
GND
0.6
V (max)
IIN(1)
Logical “1” Input Current
VIN = VCC
2
µA (max)
IIN(0)
Logical “0” Input Current
VIN = 0 V
-2
µA (max)
ALL DIGITAL INPUTS
CIN
Input Capacitance
20
pF
ALL DIGITAL OUTPUTS
IOH
High Level Output Current
VOH = VCC
100
µA (max)
VOL
SMBus Low Level Output Voltage
IOL = 3 mA
IOL = 6 mA
0.4
0.6
V (max)
5
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LM82
Logic Electrical Characteristics
(Continued)
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 TA = TJ = TMIN to TMAX; all other limits TA = TJ = +25˚C, unless otherwise noted. 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 I2C or SMBus
bus specifications.
Symbol
Parameter
fSMB
SMBus Clock Frequency
tLOW
SMBus Clock Low Time
Conditions
Typical
Limits
Units
(Note 6)
(Note 7)
(Limit)
100
10
kHz (max)
kHz (min)
1.3
25
µs (min)
ms (max)
10
ms (max)
10 % to 10 %
tLOWMEXT Cumulative Clock Low Extend Time
tHIGH
SMBus Clock High Time
90 % to 90%
tR,SMB
SMBus Rise Time
10% to 90%
1
tF,SMB
SMBus Fall Time
90% to 10%
0.3
tOF
Output Fall Time
CL = 400 pF,
IO = 3 mA
tTIMEOUT
SMBData and SMBCLK Time Low for
Reset of Serial Interface (Note 12)
t1
SMBCLK (Clock) Period
10
µs (min)
t2,
tSU;DAT
Data In Setup Time to SMBCLK High
100
ns (min)
t3,
tHD;DAT
Data Out Stable after SMBCLK Low
300
TBD
ns (min)
ns (max)
t4,
tHD;STA
SMBData Low Setup Time to SMBCLK
Low
100
ns (min)
t5,
tSU;STO
SMBData High Delay Time after SMBCLK
High (Stop Condition Setup)
100
ns (min)
t6,
tSU;STA
SMBus Start-Condition Setup Time
0.6
µs (min)
tBUF
SMBus Free Time
1.3
µs (min)
0.6
µs (min)
µs (max)
ns (max)
250
ns (max)
25
40
ms (min)
ms (max)
SMBus Communication
10129704
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LM82
Logic Electrical Characteristics
(Continued)
SMBus TIMEOUT
10129707
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 > VCC), 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.
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 and ADD0. Doing so by more than 50 mV may corrupt a temperature
or voltage measurement.
Pin Name
D1
D2
D3
D4
Pin Name
NC (pins 1 & 5)
D1
T_CRIT_A & INT
VCC
x
SMBData
D+
x
x
x
NC (pins 9 & 15)
D−
x
x
x
ADD0, ADD1
x
x
x
x
D2
D3
D4
x
x
x
x
x
x
SMBCLK
x
x
NC (pin 13)
x
x
Note: An x indicates that the diode exists.
10129713
FIGURE 1. ESD Protection Input Structure
Note 3: See 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: 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
Figure 3 .
Note 6: Typicals are at TA = 25˚C and represent most likely parametric norm.
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LM82
Logic Electrical Characteristics
(Continued)
Note 7: Limits are guaranteed to National’s AOQL (Average Outgoing Quality Level).
Note 8: The Temperature Error will vary less than ± 1.0˚C for a variation in VCC of 3V to 3.6V from the nominal of 3.3V.
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 tTIMEOUT will cause the LM82 to reset SMBData and SMBCLK to the IDLE
state of an SMBus communication (SMBCLK and SMBData set High).
10129705
FIGURE 2. Temperature-to-Digital Transfer Function (Non-linear scale for clarity)
10129724
FIGURE 3. Printed Circuit Board Used for Thermal Resistance Specifications
2. Remote Diode (RT)
This round robin sequence takes approximately 480 ms to
complete.
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 I2C two wire
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.
1.2 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
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)
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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 conversion is below the T_CRIT setpoint, as shown in
Figure 6. Figure 7 shows a simplified logic diagram of the
T_CRIT_A and related circuitry.
(Continued)
less than or equal to it’s corresponding HIGH setpoint, as
shown in Figure 4. Figure 5 shows a simplified logic diagram
for the INT output and related circuitry.
10129706
* Note: Status Register Bits are reset by a read of Status Register where
bit is located.
10129714
* Note: Status Register Bits are reset by a read of Status Register where
bit is located.
FIGURE 6. T_CRIT_A Temperature Response Diagram
FIGURE 4. INT Temperature Response Diagram
10129721
FIGURE 5. INT output related circuitry logic diagram
10129720
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.
FIGURE 7. T_CRIT_A output related circuitry logic
diagram
Located in the Configuration Register are the mask bits for
each temperature reading, seeSection 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.
1.3 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.
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LM82
1.0 Functional Description
LM82
1.0 Functional Description
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.
(Continued)
1.4 POWER ON RESET DEFAULT STATES
LM82 always powers up to these known default states:
1. Command Register set to 00h
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:
2.
3.
Local Temperature set to 0˚C
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.
6. Local and Remote T_CRIT set to 127˚C
Temperature
Digital Output
Binary
Hex
+125˚C
0111 1101
7Dh
1.5 SMBus INTERFACE
+25˚C
0001 1001
19h
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 VCC for a
high, (1), or left floating (TRI-LEVEL).
Therefore, the complete slave address is:
+1˚C
0000 0001
01h
0˚C
0000 0000
00h
A6
A5
A4
1
A2
A1
MSB
A0
and is selected as follows:
LM82 SMBus Slave
Address
ADD0
ADD1
0
0
001 1000
0
TRI-LEVEL
001 1001
1111 1111
FFh
1110 0111
E7h
−55˚C
1100 1001
C9h
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.
LSB
Address Select Pin State
−1˚C
−25˚C
A6:A0 binary
0
1
001 1010
TRI-LEVEL
0
010 1001
1.8 DIODE FAULT DETECTION
TRI-LEVEL
TRI-LEVEL
010 1010
TRI-LEVEL
1
010 1011
1
0
100 1100
1
TRI-LEVEL
100 1101
1
1
100 1110
Before each external conversion the LM82 goes through an
external diode fault detection sequence. If D+ input is
shorted to VCC or floating then the temperature reading will
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.
The LM82 latches the state of the address select pins during
the first read or write on the SMBus. Changing the state of
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LM82
1.0 Functional Description
(Continued)
1.9 COMMUNICATING with the LM82
10129709
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 Local Temperature
Register. 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.
A Write 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 correct (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 frequently read
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
address 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).
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 (tTIMEOUT). The LM82 may or may not reset the state of
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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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
0
P5
P4
P3
P2
P1
P0
Command Select
P0-P7: Command Select
Command Select Power On Default State
Address
Register Name
Register Function
< P7:P0 > hex
< D7:D0 > binary
< D7:D0 > decimal
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
04h
0000 0000
0
05h
0111 1111
127
RLHS
06h
07h
0111 1111
127
RRHS
Read Remote HIGH Setpoint
WC
Write Configuration
Reserved
0000 0000
0Ah
0Bh
Reserved
0111 1111
127
WLHS
Write Local HIGH Setpoint
0111 1111
127
WRHS
Write Remote HIGH Setpoint
0Ch
0Dh
Reserved
0Eh-2Fh
30h-31h
Reserved for Future Use
0000 0000
0
Reserved
0000 0000
0
Reserved
32h-34h
35h
Reserved for Future Use
36h-37h
38h
Reserved for Future Use
0111 1111
127
0111 1111
127
0111 1111
127
Reserved
39h
3Ah
Reserved for Future Use
Reserved
3Bh-41h
42h
Reserved for Future Use
RTCS
43h-4Fh
50h
0111 1111
127
0111 1111
127
Reserved
Reserved for Future Use
Reserved
53h-59h
5Ah
Reserved for Future Use
0111 1111
127
WTCS
5Ch-6Fh and
F0h-FDh
FEh
FFh
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Read T_CRIT Setpoint
Reserved for Future Use
51h
52h
Read Local HIGH Setpoint
Reserved
08h
09h
Read Configuration
Reserved
Write T_CRIT Setpoint
Reserved for Future Use
0000 0001
1
RMID
Read Manufacturers ID
1
RSR
Read Stepping or Die Revision
Code
12
LM82
2.0 LM82 Registers
(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 ).
2.5 CONFIGURATION REGISTER
(Read Address 03h/Write Address 09h):
D7
D6
D5
D4
D3
D2
D1
D0
INT mask
0
Remote
T_CRIT_A
mask
Remote
T_CRIT_A
mask
Remote
T_CRIT_A
mask
Local
T_CRIT_A
mask
INT Inversion
0
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
function 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
function 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. A low 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.
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.
13
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LM82
3.0 SMBus Timing Diagrams
10129710
(a) Serial Bus Write to the internal Command Register followed by a the Data Byte
10129711
(b) Serial Bus Write to the internal Command Register
10129712
(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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14
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 Figure 9. A discrete diode can also be
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.
The technique used in today’s remote temperature sensors
is to measure the change in VBE at two different operating
points of a diode. For a bias current ratio of N:1, this difference is given as:
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 ∆VBE and converts
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
∆VBE is proportional to both η and T, the variations in η
cannot 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:
TACC = ± 3˚C + ( ± 1% of 298 ˚K) = ± 6 ˚C
.
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.
4.2 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 VCCpin and the recommended 2.2 nF
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 actually 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.
10129715
FIGURE 9. 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.
15
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LM82
4.1 ACCURACY EFFECTS OF DIODE NON-IDEALITY
FACTOR
4.0 Application Hints
LM82
4.0 Application Hints
(Continued)
Noise coupling into the digital lines greater than 300mVp-p
(typical hysteresis), overshoot greater than 500mV above
VCC, and undershoot less than 500mV below GND, may
prevent 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 speed data
communications cross at right angles to the SMBData and
SMBCLK lines.
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.
6.
Avoid running diode traces close to or parallel to high
speed digital and bus lines. Diode traces should be kept
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.
10129717
FIGURE 10. Ideal Diode Trace Layout
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16
inches (millimeters) unless otherwise noted
16-Lead QSOP Package
Order Number LM82CIMQA or LM82CIMQAX
NS Package Number MQA16
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LM82 Remote Diode and Local Digital Temperature Sensor with Two-Wire Interface
Physical Dimensions