LM32
LM32 Dual Thermal Diode Temperature Sensor with Bus
Literature Number: SNIS132D
LM32
October 20, 2011
Dual Thermal Diode Temperature Sensor with Bus
General Description
Features
The LM32 is a digital temperature sensor that measures 3
temperature zones and has a single-wire interface SensorPath bus. SensorPath data is pulse width encoded, thereby
allowing the LM32 to be easily connected to many general
purpose micro-controllers. Several Winbond Electronics Super I/O products include a fully integrated SensorPath master,
that when connected to an LM32 can realize a hardware
monitor function that includes limit checking for measured
values, autonomous fan speed control and many other functions.
The LM32 measures the temperature of its own die as well as
two external devices such as a processor thermal diode or a
diode connected transistor. The LM32 can resolve temperatures up to 255°C and down to -256°C. The operating temperature range of the LM32 is 0°C to +125°C. The address
programming pin allows two LM32s to be placed on one SensorPath bus.
■ SensorPath Interface
■
■
■
■
■
— 2 hardware programmable addresses
2 remote diode temperature sensor zones
Internal local temperature zone
0.5 °C resolution
Measures temperatures up to 140 °C
14-lead TSSOP package
Key Specifications
Temperature Sensor Accuracy
Temperature Range:
LM32 junction
Remote Temp Accuracy
■ Power Supply Voltage
■ Average Power Supply Current
■ Conversion Time (all Channels)
±3 °C (max)
0 °C to +85 °C
0 °C to +100 °C
+3.0 V to +3.6 V
0.5 mA (typ)
22.5ms to 1456ms
Applications
■ Microprocessor based equipment
(Motherboards, Video Cards, Base-stations, Routers,
ATMs, Point of Sale, …)
■ Power Supplies
Typical Application
20071101
SensorPath® is a registered trademark of National Semiconductor Corporation.
© 2011 National Semiconductor Corporation
200711
200711 Version 5 Revision 2
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Print Date/Time: 2011/10/20 14:02:05
LM32 Dual Thermal Diode Temperature Sensor with Bus
OBSOLETE
LM32
Connection Diagram
Order
Number
Package
Marking
TSSOP-14
NS
Package
Number
Transport
Media
LM32CIMT
LM32
CIMT
MTC14C
94 units per
rail
LM32CIMTX
LM32
CIMT
MTC14C
2500 units in
tape and reel
20071102
Top View
National Package Number MTC14C
Pin Descriptions
Pin Number
Pin Name
Description
Typical Connection
1, 6, 7,12, 13, 14
NC
No Connect
May be tied to V+, GND or left floating
2
GND
Ground
System ground
3
V+/+3.3V_SBY
Positive power supply pin
Connected system 3.3 V standby power and to
a 0.1 µF bypass capacitor in parallel with 100
pF. A bulk capacitance of approximately 10 µF
needs to be in the near vicinity of the LM32.
4
SWD
SensorPath Bus line; Open-drain
output
Super I/O, Pull-up resistor, 1.6k
5
ADD
Digital input - device number select Pull-up to 3.3 V or pull-down to GND resistor,
input for the serial bus device number 10k; must never be left floating
8, 10
D1-, D2-
Thermal diode analog voltage output Remote Thermal Diode cathode (THERM_DC)
and negative monitoring input
- Diode 1 should always be connected to the
processor thermal diode. Diode 2 may be
connected to an MMBT3904 or GPU thermal
diode. A 100 pF capacitor should be connected
between respective D- and D+ for noise filtering.
9, 11
D1+, D2+
Thermal diode analog current output Remote Thermal Diode anode (THERM_DA) and positive monitoring input
Diode 1 should always be connected to the
processor thermal diode. Diode 2 may be
connected to an MMBT3904 or GPU thermal
diode. A 100 pF capacitor should be connected
between respective D- and D+ for noise filtering.
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LM32
Block Diagram
20071103
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LM32
Storage Temperature
−65°C to +150°C
Soldering process must comply with National's reflow
temperature profile specifications. Refer to
www.national.com/packaging/. (Note 6)
Absolute Maximum Ratings
(Note 2, Note 1)
Supply Voltage (V+)
Voltage at Any Digital Input or
Output Pin
Voltage on D1+ and D2+
Current on D1- and D2Input Current per Pin(Note 3)
Package Input Current (Note 3)
Package Power Dissipation
Output Sink Current
ESD Susceptibility (Note 5)
Human Body Model
Machine Model
−0.5 V to 6.0 V
Operating Ratings
−0.5 V to 6.0 V
−0.5 V to (V+ + 0.05 V)
±1 mA
±5 mA
±30 mA
(Note 4)
10 mA
(Note 1, Note 2)
Temperature Range for Electrical Characteristics
2500 V
250 V
LM32CIMT (TMIN≤TA≤TMAX)
Operating Temperature Range
0°C ≤ TA ≤ +85°C
0°C ≤ TA ≤ +125°C
Remote Diode Temperature (TD)
Range
Supply Voltage Range (V+)
-5°C ≤TD ≤+140 °C
+3.0 V to +3.6 V
DC Electrical Characteristics
The following specifications apply for V+ = +3.0 VDC to +3.6 VDC, and all analog source impedance RS = 50 Ω unless otherwise
specified in the conditions. Boldface limits apply for LM32CIMT TA = TJ = TMIN=0°C to TMAX=85°C; all other limits TA = +25°C.
TA is the ambient temperature of the LM32; TJ is the junction temperature of the LM32; TD is the junction temperature of the remote
thermal diode.
POWER SUPPLY CHARACTERISTICS
Symbol
V+
Parameter
Conditions
Power Supply Voltage
Typical
(Note 7)
Limits
(Note 8)
Units
(Limit)
3.3
3.0
3.6
V (min)
V (max)
260
420
µA (max)
I+Shutdown
Shutdown Power Supply Current
SensorPath Bus Inactive
(Note 9)
I+Average
Average Power Supply Current
SensorPath Bus Inactive; all
sensors enabled; tCONV=182 ms;
(Note 9)
900
µA (max)
Peak Power Supply Current
SensorPath Bus Inactive
(Note 9)
3.3
mA (max)
I+Peak
1.6
V (min)
2.8
V (max)
Typical
(Note 7)
Limits
(Note 8)
Units
(Limits)
Temperature Accuracy Using the Remote Thermal TJ = 0°C to +85°C TD = +25°C
Diode, see (Note 11) for Thermal Diode Processor T = 0°C to +85°C T = 0°C to +100°C
J
D
Type.
TJ = 0°C to +85°C TD = +100°C to
+125°C
±1
±2.5
°C (max)
±3
°C (max)
±4
°C (max)
Temperature Accuracy Using the Local Diode
±1
±3
°C (max)
Power-On Reset Threshold Voltage
TEMPERATURE-TO-DIGITAL CONVERTER CHARACTERISTICS
Parameter
Conditions
TJ = 0°C to +85°C (Note 10)
Remote Diode and Local Temperature Resolution
D− Source Voltage
10
Bits
0.5
°C
0.7
(VD+ − VD−) = +0.65 V; High Current
Diode Source Current
Low Current
11.75
Diode Source Current High Current to Low Current
Ratio
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V
280
µA (max)
µA
Symbol
Parameter
VIH
SWD Logical High Input Voltage
VIL
SWD Logical Low Input Voltage
Conditions
Typical
(Note 7)
Limits
(Note 8)
Units
(Limit)
2.1
V (min)
V+ + 0.5
V (max)
0.8
V (max)
-0.5
V (min)
VIH
ADD Logical High Input Voltage
90% x V+
V (min)
VIL
ADD Logical Low Input Voltage
10% x V+
V (max)
±10
µA (max)
VHYST
IL
CIN
Input Hysteresis
300
mV
SWD and ADD Input Current
GND ≤ VIN ≤ V+
±0.005
SWD Input Current with V+ Open or
Grounded
GND ≤ VIN ≤ 3.6V,
and V+ Open or
GND
±0.005
µA
10
pF
Digital Input Capacitance
SWD DIGITAL OUTPUT CHARACTERISTICS
Symbol
Parameter
VOL
Open-drain Output Logic “Low”
Voltage
IOH
Open-drain Output Off Current
COUT
Conditions
Typical
(Note 7)
I OL = 4mA
I OL = 50µA
±0.005
Digital Output Capacitance
Limits
(Note 8)
Units
(Limit)
0.4
V (max)
0.2
V (max)
±10
µA (max)
10
pF
AC Electrical Characteristics
The following specification apply for V+ = +3.0 VDC to +3.6 VDC, unless otherwise specified. Boldface limits apply for
TA = TJ = TMIN=0°C to TMAX=85°C; all other limits TA = TJ = 25°C. The SensorPath Characteristics conform to the SensorPath
specification revision 0.98. Please refer to that speciation for further details.
Symbol
Parameter
Conditions
Typical
(Note 7)
Limits
(Note 8)
Units
(Limits)
182
163.8
ms (min)
200.2
ms (max)
HARDWARE MONITOR CHARACTERISTICS
tCONV
Total Monitoring Cycle Time (Note 12)
All Temperature readings
(Default)
SensorPath Bus CHARACTERISTICS
tf
SWD fall time (Note 15)
Rpull-up=1.25 kΩ ±30%,
CL=400 pF
300
ns (max)
tr
SWD rise time (Note 15)
Rpull-up=1.25 kΩ ±30%,
CL=400 pF
1000
ns (max)
µs (min)
tINACT
Minimum inactive time (bus at high level)
guaranteed by the slave before an attention
request
11
tMtr0
Master drive for Data Bit 0 write and for Data
Bit 0-1read
11.8
µs (min)
17.0
µs (max)
Master drive for Data Bit 1 write
35.4
µs (min)
tMtr1
48.9
µs (max)
tSFEdet
Time allowed for LM32 activity detection
9.6
µs (max)
tSLout1
LM32 drive for Data Bit 1 read by master
28.3
µs (min)
38.3
µs (max)
tMtrS
tSLoutA
Master drive for Start Bit
LM32 drive for Attention Request
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80
µs (min)
109
µs (max)
165
µs (min)
228
µs (max)
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LM32
SWD and ADD DIGITAL INPUT CHARACTERISTICS
LM32
Symbol
Parameter
tRST
tRST_MAX
Conditions
Typical
(Note 7)
Limits
(Note 8)
Units
(Limits)
Master or LM32 drive for Reset
354
µs (min)
Maximum drive of SWD by an LM32, after the
power supply is raised above 3V
500
ms (max)
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 performance limits. For guaranteed specifications and test conditions, see the Electrical Characteristics. The guaranteed
specifications apply only for the test conditions listed. Some performance characteristics may degrade when the device is not operated under the listed test
conditions.
Note 2: All voltages are measured with respect to GND, unless otherwise noted.
Note 3: When the input voltage (VIN) at any pin exceeds the power supplies (VIN < GND or VIN > V+), the current at that pin should be limited to 5 mA. Parasitic
components and/or ESD protection circuitry are shown below for the LM32's pins. The nominal breakdown voltage of the zener is 6.5 V. SNP stands for snapback device.
PIN
#
Pin
Name
Pin
Circuit
1
NC
A
2
GND
B
3
V+/
3.3V SB
B
4
SWD
A
5
ADD
A
6
NC
none
7
NC
none
8
D1-
C
9
D1+
D
10
D2-
C
11
D2+
D
12
NC
none
13
NC
none
14
NC
A
All Input Structure Circuits
Note 4: Thermal resistance junction-to-ambient in still air when attached to a printed circuit board with 1 oz. foil is 148 °C/W.
Note 5: Human body model, 100 pF discharged through a 1.5 kΩ resistor. Machine model, 200 pF discharged directly into each pin.
Note 6: Reflow temperature profiles are different for lead-free and non lead-free packages.
Note 7: “Typicals” are at TA = 25°C and represent most likely parametric norm. They are to be used as general reference values not for critical design calculations.
Note 8: Limits are guaranteed to National's AOQL (Average Outgoing Quality Level).
Note 9: The supply current will not increase substantially with a SensorPath transaction.
Note 10: Local temperature accuracy does not include the effects of self-heating. The rise in temperature due to self-heating is the product of the internal power
dissipation of the LM32 and the thermal resistance. See (Note 4) for the thermal resistance to be used in the self-heating calculation.
Note 11: The accuracy of the LM32CIMT is guaranteed when using the thermal diode of an Intel 90 nm Pentium 4 processor or any thermal diode with a nonideality factor of 1.011 and series resistance of 3.33Ω. When using a MMBT3904 type transistor as a thermal diode the error band will be typically shifted by
-4.5 °C.
Note 12: This specification is provided only to indicate how often temperature data are updated.
Note 13: The output fall time is measured from (VIH min) to (VIL max).
Note 14: The output rise time is measured from (VIL max) to (VIH min).
Note 15: The rise and fall times are not tested but guaranteed by design.
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LM32
Timing Diagrams
20071104
FIGURE 1. Timing for Data Bits 0, 1 and Start Bit. See Section 1.2 "SensorPath BIT SIGNALING" for further details.
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LM32
20071105
FIGURE 2. Timing for Attention Request and Reset. See Section 1.2 "SensorPath BIT SIGNALING" for further details.
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LM32
Typical Performance Characteristics
Remote Diode Temperature Reading Sensitivity to
Diode Filter Capacitance
Thermal Diode Capacitor or PCB Leakage Current Effect
on Remote Diode Temperature Reading
20071121
20071122
1.0 Functional Description
The LM32 measures 3 temperature zones. The LM32 uses a
ΔVbe temperature sensing method. A differential voltage, representing temperature, is digitized using a Sigma-Delta analog to digital converter. The digitized data can be retrieved
over a simple single-wire interface called SensorPath. SensorPath was originally defined by National Semiconductor
and is optimized for hardware monitoring.
The LM32 has one address pin to allow up to two LM32s to
be connected to one SensorPath bus. The physical interface
of SensorPath's SWD signal is identical to the familiar industry
standard SMBus SMBDAT signal. The digital information is
encoded in the pulse width of the signal being transmitted.
Every bit can be synchronized by the master simplifying the
implementation of the master when using a micro-controller.
For micro-controller's with greater functionality an asynchronous attention signal can be transmitted by the LM32 to
interrupt the micro-controller and notify it that temperature
data has been updated in the readout registers.
To optimize the LM32's power consumption to the system requirements, the LM32 has a shutdown mode and supports
multiple conversion rates.
20071107
FIGURE 3. SensorPath SWD simplified schematic
1.2 SensorPath BIT SIGNALING
Signals are transmitted over SensorPath using pulse-width
encoding. There are five types of "bit signals":
• Data Bit 0
• Data Bit 1
• Start Bit
• Attention Request
• Reset
All the "bit signals" involve driving the bus to a low level. The
duration of the low level differentiates between the different
"bit-signals". Each "bit signal" has a fixed pulse width. SensorPath supports a Bus Reset Operation and Clock Training
sequence that allows the slave device to synchronize its internal clock rate to the master. Since the LM32 meets the
±15% timing requirements of SensorPath, the LM32 does not
require the Clock Training sequence and does not support
this feature. This section defines the "bit signal" behavior in
all the modes. Please refer to the timing diagrams in the Electrical Characteristics section (Figure 1 and Figure 2) while
going through this section. Note that the timing diagrams for
the different types of "bit signals" are shown together to better
highlight the timing relationships between them. However, the
different types of "bit signals" appear on SWD at different
points in time. These timing diagrams show the signals as
driven by the master and the LM32 slave as well as the signal
as seen when probing SWD. Signal labels that begin with the
label Mout_ depict a drive by the master. Signal labels that
begin with the label Slv_ depict the drive by the LM32. All
other signals show what would be seen when probing SWD
1.1 SensorPath BUS SWD
SWD is the Single Wire Data line used for communication.
SensorPath uses 3.3V single-ended signaling, with a pull-up
resistor and open-drain low-side drive (see Figure 3). For timing purposes SensorPath is designed for capacitive loads
(CL) of up to 400pF. Note that in many cases a 3.3V standby
rail of the PC will be used as a power supply for both the sensor and the master. Logic high and low voltage levels for SWD
are TTL compatible. The master may provide an internal pullup resistor. In this case the external resistor is not needed.
The minimum value of the pull-up resistor must take into account the maximum allowable output load current of 4mA.
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LM32
for a particular function (e.g. "Master Wr 0" is the Master
transmitting a Data Bit with the value of 0).
treated as a Start Bit. The master may attempt to send the
Start Bit at a later time.
1.2.1 Bus Inactive
The bus is inactive when the SWD signal is high for a period
of at least tINACT. The bus is inactive between each "bit signal".
1.2.4 Attention Request
The LM32 may initiate an Attention Request when the SensorPath bus is inactive.
Note that a Data Bit, or Start Bit, from the master may start
simultaneously with an Attention Request from the LM32. In
addition, two LM32s may start an Attention Request simultaneously. Due to its length, the Attention Request has priority
over any other "bit signal", except Reset. Conflict with Data
Bits and Start Bits are detected by all the devices, to allow the
bits to be ignored and re-issued by their originator.
The LM32 will either check to see that the bus is inactive before starting an Attention Request, or start the Attention Request within the tSFEdet time interval after SWD becomes
active. The LM32 will drive the signal low for tSLoutA time. After
this, both the master and the LM32 must monitor the bus for
a Reset Condition. If a Reset condition is detected, the current
"bit signal" is not treated as an Attention Request.
After Reset, an Attention Request can not be sent before the
master has sent 14 Data Bits on the bus. See Section 1.3.5
for further details on Attention Request generation.
1.2.2 Data Bit 0 and 1
All Data Bit signal transfers are started by the master. A Data
Bit 0 is indicated by a "short" pulse; a Data Bit 1 is indicated
by a longer pulse. The direction of the bit is relative to the
master, as follows:
• Data Write - a Data Bit transferred from the master to the
LM32.
• Data Read - a Data Bit transferred from the LM32 to the
master.
A master must monitor the bus as inactive before starting a
Data Bit (Read or Write).
A master initiates a data write by driving the bus active (low
level) for the period that matches the data value (tMtr0 or tMtr1
for a write of "0" or "1", respectively). The LM32 will detect that
the SWD becomes active within a period of tSFEdet, and will
start measuring the duration that the SWD is active in order
to detect the data value.
A master initiates a data read by driving the bus for a period
of tMtr0. The LM32 will detect that the SWD becomes active
within a period of tSFEdet. For a data read of "0", the LM32 will
not drive the SWD. For a data read of "1" the LM32 will start
within tSFEdet to drive the SWD low for a period of tSLout1. Both
master and LM32 must monitor the time at which the bus becomes inactive to identify a data read of "0" or "1".
During each Data Bit, both the master and all the LM32s must
monitor the bus (the master for Attention Request and Reset;
the LM32s for Start Bit, Attention Request and Reset) by
measuring the time SWD is active (low). If a Start Bit, Attention
Requests or Reset "bit signal" is detected, the current "bit
signal" is not treated as a Data Bit.
Note that the bit rate of the protocol varies depending on the
data transferred. Thus, the LM32 has a value of "0" in reserved or unused register bits for bus bandwidth efficiency.
1.2.5 Bus Reset
The LM32 issues a Reset at power up. The master must also
generate a Bus Reset at power-up for at least the minimum
reset time, it must not rely on the LM32. SensorPath puts no
limitation on the maximum reset time of the master. Following
a Bus Reset, the LM32 may generate an Attention Request
only after the master has sent 14 Data Bits on the bus. See
Section 1.3.5 for further details on Attention Request generation.
1.3 SensorPath BUS TRANSACTIONS
SensorPath is designed to work with a single master and up
to seven slave devices. Each slave has a unique address. The
LM32 supports up to 2 device addresses that are selected by
the state of the address pin ADD. The Register Set of the
LM32 is defined in Section 2.0.
1.3.1 Bus Reset Operation
A Bus Reset Operation is global on the bus and affects only
the communication interface of all the devices connected to
it. The Bus Reset operation does not affect either the contents
of the device registers, or device operation, to the extent defined in LM32 Register Set, see Section 2.0.
The Bus Reset operation is performed by generating a Reset
signal on the bus. The master must apply Reset after powerup, and before it starts operation. The Reset signal end will
be monitored by all the LM32s on the bus.
After the Reset Signal the SensorPath specification requires
that the master send a sequence of 8 Data Bits with a value
of "0", without a preceding Start Bit. This is required to enable
slaves that "train" their clocks to the bit timing. The LM32 does
not require nor does it support clock training.
1.2.3 Start Bit
A master must monitor the bus as inactive before beginning
a Start Bit.
The master uses a Start Bit to indicate the beginning of a
transfer. LM32s will monitor for Start Bits all the time, to allow
synchronization of transactions with the master. If a Start Bit
occurs in the middle of a transaction, the LM32 being addressed will abort the current transaction. In this case the
transaction is not "completed" by the LM32 (see Section 1.3
"SensorPath Bus Transactions").
During each Start Bit, both the master and all the LM32s must
monitor the bus for Attention Request and Reset, by measuring the time SWD is active (low). If an Attention Request or
Reset condition is detected, the current "bit signal" is not
20071108
FIGURE 4. Bus Reset Transaction
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Acknowledge (ACK) During a read transaction the ACK
bit is sent by the master indicating that the EP bit was
received and was found to be correct, when compared to
the data preceding it, and that no conflict was detected on
the bus (excluding Attention Request - see Section 1.3.5
"Attention Request Transaction"). A read transfer is
considered "complete" only when the ACK bit is received.
A transaction that was not positively acknowledged is not
considered "complete" by the LM32 and following are
performed:
— The BER bit in the LM32 Device Status register is set
— The LM32 generates an Attention Request before, or
together with the Start Bit of the next transaction
A transaction that was not positively acknowledged is also
not considered "complete" by the master (i.e. internal
operations related to the transaction are not performed).
The transaction may be repeated by the master, after
detecting the source of the Attention Request (the LM32
that has a set BER bit in the Device Status register). Note
that the SensorPath protocol neither forces, nor
automates re-execution of the transaction by the master.
The values of the ACK bit are:
— 1: Data was received correctly
— 0: An error was detected (no-acknowledge).
20071109
FIGURE 5. Read Transaction, master reads data from LM32
1.3.3 Write Transaction
In a write transaction, the master writes data to a register at
a specified address in the LM32. A write transaction begins
with a Start Bit and ends with an ACK Data Bit, as show in
Figure 6.
• Device Number This is the address of the slave device
accessed. Address "000" is a broadcast address and is
responded to by all the slave devices. The LM32 responds
to broadcast messages to the Device Control Register.
• Internal Address This is the register address in the LM32
that will be written.
• Read/Write (R/W) A "0" data bit directs a write
transaction.
• Data Bits This is the data written to the LM32 register,
are driven by the master. Data is transferred serially with
the most significant bit first. The number of data bits may
vary from one address to another, based on the size of the
register in the LM32. This allows throughput optimization
based on the information that needs to be written.
The LM32 supports 8-bit or 16-bit data fields, as described
in Section 2.0 "Register Set".
• Even Parity (EP) This data bit is based on all preceding
bits (Device Number, Internal Address, Read/Write and
Data bits) and the Even Parity bit itself. The parity (number
of 1's) of all the preceding bits and the parity bit must be
even - i.e. the result must be 0. During a write transaction,
•
the EP bit is sent by the master to the LM32 to allow the
LM32 to check the received data before using it.
Acknowledge (ACK) During the write transaction the
ACK bit is sent by the LM32 indicating to the master that
the EP was received and was found correct, and that no
conflict was detected on the bus (excluding Attention
Request - see Section 1.3.5 "Attention Request
Transaction"). A write transfer is considered "completed"
only when the ACK bit is generated. A transaction that was
not positively acknowledged is not considered complete
by the LM32 (i.e. internal operation related to the
transaction are not performed) and the following are
performed:
— The BER bit in the LM32 Device Status register is set;
— The LM32 generates an Attention Request before, or
together with the Start Bit of the next transaction
A transaction that was not positively acknowledged is also
not considered "complete" by the master (i.e. internal
operations related to the transaction are not performed).
The transaction may be repeated by the master, after
detecting the source of the Attention Request (the LM32
that has a set BER bit in the Device Status register). Note
that the SensorPath protocol neither forces, nor
automates re-execution of the transaction by the master.
The values of the ACK bit are:
— 1: Data was received correctly;
— 0: An error was detected (no-acknowledge).
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LM32
•
1.3.2 Read Transaction
During a read transaction, the master reads data from a register at a specified address within a slave. A read transaction
begins with a Start Bit and ends with an ACK bit, as shown in
Figure 5.
• Device Number This is the address of the LM32 device
accessed. Address "000" is a broadcast address and can
be responded to by all the slave devices. The LM32
ignores the broadcast address during a read transaction.
• Internal Address The address of a register within the
LM32 that is read.
• Read/Write (R/W) A "1" indicates a read transaction.
• Data Bits During a read transaction the data bits are
driven by the LM32. Data is transferred serially with the
most significant bit first. This allows throughput
optimization based on the information that needs to be
read.
The LM32 supports 8-bit or 16-bit data fields, as described
in Section 2.0 "Register Set".
• Even Parity (EP) This bit is based on all preceding bits
(device number, internal address, Read/Write and data
bits) and the parity bit itself. The parity -number of 1's - of
all the preceding bits and the parity bit must be even - i.e.,
the result must be 0. During a read transaction, the EP bit
is sent by the LM32 to the master to allow the master to
check the received data before using it.
LM32
20071110
FIGURE 6. Write Transaction, master write data to LM32
3.
1.3.4 Read and Write Transaction Exceptions
This section describes master and LM32 handling of special
bus conditions, encountered during either Read or Write
transactions.
If an LM32 receives a Start Bit in the middle of a transaction,
it aborts the current transaction (the LM32 does not "complete" the current transaction) and begins a new transaction.
Although not recommend for SensorPath normal operation,
this situation is legitimate, therefore it is not flagged as an
error by the LM32 and Attention Request is not generated in
response to it. The master generating the Start Bit, is responsible for handling the not "complete" transaction at a "higher
level".
If LM32 receives more than the expected number of data bits
(defined by the size of the accessed register), it ignores the
unnecessary bits. In this case, if both master and LM32 identify correct EP and ACK bits they "complete" the transaction.
However, in most cases, the additional data bits differ from
the correct EP and ACK bits. In this case, both the master and
the LM32 do not "complete" the transaction. In addition, the
LM32 performs the following:
• the BER bit in the LM32 Device Status register is set
• the LM32 generates an Attention Request
If the LM32 receives less than the expected number of data
bits (defined by the size of the accessed register), it waits indefinitely for the missing bits to be sent by the master. If then
the master sends the missing bits, together with the correct
EP/ACK bits, both master and LM32 "complete" the transaction. However, if the master starts a new transaction generating a Start Bit, the LM32 aborts the current transaction (the
LM32 does not "complete" the current transaction) and begins
the new transaction. The master is not notified by the LM32
of the incomplete transaction.
OR
1. A bus error event occurred, and
2. the "physical" condition for an Attention Request is met
(i.e., the bus is inactive), and
3. At the first time 2. is met after 1 occurred, there has not
been a Bus Reset.
All devices (master or slave) must monitor the bus for an Attention Request signal. The following notes clarify the intended system operation that uses the Attention Request
Indication.
• Masters are expected to use the attention request as a
trigger to read results from the LM32. This is done in a
sequence that covers all LM32s. This sequence is referred
to as "master sensor read sequence".
• After an Attention Request is sent by an LM32 until after
the next read from the Device Status register the LM32
does not send Attention Requests for a function event
since it is guaranteed that the master will read the Status
register as part of the master sensor read sequence. Note
that the LM32 will send an attention for BER, regardless
of the Status register read, to help the master with any
error recovery operations and prevent deadlocks.
• A master must record the Attention Request event. It must
then scan all slave devices in the system by reading their
Device Status register and must handle any pending event
in them before it may assume that there are no more
events to handle.
Note: there is no indication of which slave has sent the request. The requirement that multiple requests are not sent
allows the master to know within one scan of register reads
that there are no more pending events.
1.3.5 Attention Request Transaction
Attention Request is generated by the LM32 when it needs
the attention of the master. The master and all LM32s must
monitor the Attention Request to allow bit re-sending in case
of simultaneous start with a Data Bit or Start Bit transfer. Refer
to the "Attention Request" section, Section 1.2.4 in the "Bit
Signaling" portion of the data sheet.
The LM32 will generate an Attention Request using the following rules:
1. A Function event that sets the Status Flag has occurred
and Attention Request is enabled and
2. The "physical" condition for an Attention Request is met
(i.e., the bus is inactive), and
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At the first time 2 is met after 1 occurred, there has not
been an Attention request on the bus since a read of the
Device Status register, or since a Bus Reset.
1.3.6 Fixed Device Number Setting
The LM32 device number is defined by strapping of the ADD
pin. The LM32 will wake (after Device Reset) with the Device
Number field of the Device Number register set to the address
as designated in Section 2.3 "Device Number". It is the responsibility of the system designer to avoid having two devices with the same Device Number on the bus.
Devices should be detected by the master by a read operation
of the Device Number register. The read returns "000" if there
is no device at that address on the bus (the EP bit must be
ignored).
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LM32
2.0 Register Set
2.1 REGISTER SET SUMMARY
R/
W
P
O
R
Val
000 000 Device
00h
Number
R
*
000 001 Manufactur
01h
er ID
R 100Bh
000 010
Device ID
02h
R
23h
000 011 Capabilities
03h
Fixed
R
01h
Reg
Add
Register
Name
R
0h
000 101 Device
05h
Control
R/
W
0h
Processor/
Remote
Temperatur
e Data
001 001
Readout
09h
Local
Temperatur
e Data
Readout
Bit
13
Bit
12
Bit
11
Bit
Bit 0
Bit 9 Bit 8 Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1
10
LSb
Reserved
Not Available
0
0
0
0
0
0
0
0
0
0
0
0
1
0
1
1
0
0
0
1
1
1
0
0
0
0
0
0
0
0
0
0
0
0
0
Device ID
1
FuncDescriptor 1
(Temperature)
Reserved
0
0
0
0
0
0
0
0
0
0
Reserved
0
0
0
Reserved
R 0549h
0
0
0
0
0
0
# of Remotes
0
0
Reserved ERF
BER
1
0
0
Not Available
0
See Section 2.3
0
RevID
0
000 100 Device
04h
Status
Temperatur
001 000
e
08h
Capabilities
Bit
Bit
15
14
MSb
0
1
0
0
0
0
0
Int
Rout
Sen
Sign
Size
s
1
0
1
EnF
1
0
0
Res
0
10-Bits
0
0
0
0
Reserved
0
0
Shut
Low
dow
Pwr
n
MSb 128
Sign °C
R
001 010 Temperatur R/
0Ah
e Control
W
001 011
-011
111
Reserved
0Bh-1F
h
R
100 000 Conversion
20h
Rate
R/
W
100 001
-111 Undefined
Registers
111
21h-3Fh
R
0h
64°
C
32°
C
16°
C
8°C
4°C
2°C
1
°C
0
0
0
0
0
0
0
0
0
0
Re
set
1
0
0
1
Res
EF
0
0
SNUM
Res
Res Res
0
0
0
0
Reserved
0
SF1
0.5°C Resolution
Res
LSb
0.5
°C
1
0
0
EN2 EN1 EN0 ATE
Undefined
2h
Not Available
Reserved
0
0
0
0
0
0
CR1 CR0
Undefined
* Depends on state of ADD pins see Section 2.3 "Device Number".
2.2 DEVICE RESET OPERATION
A Device Reset operation is performed in the following conditions:
•
•
At device power-up.
When the Reset bit in the Device Control register is set to 1 (see Section 2.8 "Device Control").
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LM32
The Device Reset operation performs the following:
•
•
Aborts any device operation in progress and restarts device operation.
Sets all device registers to their "Reset" (default) value.
2.3 DEVICE NUMBER (Addr: 000 000; 00h)
This register is used to specify a unique address for each device on the bus.
Reg Add
Register Name
R/
W
000 000
Device Number
R
P
O
R
Val
7h or 1h
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Reserved
0
0
0
0
Bit 2
Bit 1
Bit 0
LSb
AS2
AS1
AS0
0
The value of [AS2:AS0] is determined by the setting of the ADD input pin:
TABLE 1. Device Number Assignment
ADD
[AS2:AS0]
0
001
1
111
The value of [AS2:AS0] will directly change and follow the value determined by ADD. Since this is a read only register the value
of the address cannot be changed by software.
2.4 MANUFACTURER ID (Addr: 000 001; 01h)
Reg
Add
Register
Name
000 001 Manufacture
r ID
R/
W
R
P
O
R
Val
100B
h
Bit
Bit
15
14
MSb
0
0
Bit
13
Bit
12
Bit
11
0
1
0
Bit
Bit 0
Bit 9 Bit 8 Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1
10
LSb
0
0
0
0
0
0
0
1
0
1
1
The manufacturer ID matches that assigned to National Semiconductor by the PCI SIG. This register may be used to identify the
manufacturer of the device in order to perform manufacturer specific operations.
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LM32
2.5 DEVICE ID (Addr: 000 010; 02h)
Reg
Add
Register
Name
000 010 Device ID
R/
W
P
O
R
Val
R
23h
Bit
Bit
15
14
MSb
Bit
13
Bit
12
Bit
11
0
0
Bit
Bit 0
Bit 9 Bit 8 Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1
10
LSb
RevID
0
0
0
DeviceID
0
0
0
0
0
1
0
0
0
1
1
The device ID is defined by the manufacturer of the device and is unique for each device produced by a manufacturer. Bits 15-11
identify the revision number of the die and will be incremented upon revision of the device.
Bit
Type
10-0
RO
Description
DeviceID (Device ID Value) A fixed value that identifies the device.
15-11
RO
RevID (Revision ID Value) A fixed value that identifies the device revision.
2.6 CAPABILITIES FIXED (Addr: 000 011; 03h)
Reg
Add
Register
Name
000 011 Capabilities
Fixed
R/
W
P
O
R
Val
R
1h
Bit
Bit
15
14
MSb
Bit
13
Bit
12
Bit
11
0
0
0
Bit
Bit 0
Bit 9 Bit 8 Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1
10
LSb
Reserved
0
0
0
0
FuncDescriptor1
0
0
0
0
0
0
0
0
1
The value of this register defines the capabilities of the LM32. The LM32 supports one function, that of Temperature Measurement
type. Please refer to the SensorPath specification for further details on other FuncDescriptor values.
2.7 DEVICE STATUS (Addr: 000 100; 04h)
This register is set to the reset value by a Device Reset.
Reg Add
Register Name
R/
W
000 100
Device Status
R
P
O
R
Val
Bit 7
0h
BER
Bit 6
Res
0
Bit
Type
0
RO
Bit 5
Bit 4
Bit 3
ERF1
0
Bit 2
Bit 1
Res
0
0
Bit 0
LSb
SF1
0
Description
SF1 (Status Function 1) This bit is set by a Function Event within Function 1. Event details are function dependent and are described within the function. SF1 is cleared by Device Reset or by handling the event within
the Temperature Measurement Function (see Section 2.9 for further details).
0: Status flag for Function 1 is inactive (no event).
3-1
RO
4
RO
1: Status flag for Function 1 is active indicating that a Function Event has occurred.
Reserved. Will always read "0".
ERF1 (Error Function 1) This bit is set in response to an error indication within Function 1. ERF1 is cleared
by Device Reset or by handling the error condition within the Temperature Measurement Function (see Section
2.9 for further details).
0: No error occurred in Function 1.
6-5
RO
7
RO
1: Error occurred in Function 1.
Reserved. Will always read "0".
BER (Bus Error) This bit is set when the device either generates, or receives an error indication in the ACK bit
of the transaction (i.e., no-acknowledge). BER is cleared by Device Reset or by reading the Device Status
register.
0: No transaction error occurred.
1: An ACK bit error (no-acknowledge) occurred during the last transaction.
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LM32
2.8 DEVICE CONTROL (Addr: 000 101; 05h)
This register responds to a broadcast write command (Device Number 000). Write using broadcast address is ignored by bits 15-2.
This register is set to the reset value by a Device Reset.
Reg
Add
Register
Name
000 101 Device
Control
R/
W
R/
W
P
O
R
Val
Bit
Bit
15
14
MSb
Bit
13
Bit
12
Bit
11
0
0
0
0h
Bit
10
Bit9 Bit 8 Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1
Reserved
0
0
0
0
0
0
0
0
Bit 0
LSb
EnF Res Low Shut
1
Pwr dow
n
Bit
Type
Description
0
R/W
Reset (Device Reset). When set to "1" this bit initiates a Device Reset operation ( See Section 2.2). This bit
self-clears after the Device Reset operation is completed.
Re
set
0: Normal device operation. (default)
1: Device Reset
1
R/W
The LM32 does not require a Device Reset command after power.
Shutdown (Shutdown Mode). When set to "1" this bit stops the operation of all functions and places the device
in the lowest power consumption mode.
0: Device in Active Mode. (default)
2
R/W
1: Device in Shutdown Mode.
LowPwr (Low-Power Mode). When set to "1" this bit slows the operation of all functions and places the device
in a low power consumption mode. In Low-Power Mode, the conversion rate of the LM32 is effected see Section
2.10 for further details.
0: Device in Active Mode. (default)
3
RO
4
R/W
1: Device in Low-Power Mode.
Not supported. Will always read "0".
EnF1 (Enable Function 1). When bit is set to "1" this bit Function 1 is enabled for operation. A function may
require setup before this bit is set. The function registers can be accessed even when the function is disabled.
0: Function 1 is disabled. (default)
15-5
RO
1: Function is enabled.
Not supported. Will always read "0".
2.9 TEMPERATURE MEASUREMENT FUNCTION (TYPE - 0001)
This section defines the register structure and operation of a Temperature Measurement function as it applies to the LM32. The
FuncDescriptor value of this function is ‘0001’.
2.9.1 Operation
The Temperature Measurement function as implemented in the LM32 supports 3 temperature zones, the LM32's internal temperature (LM32's junction temperature) and the remote temperature of 2 thermal diodes (stand alone transistors or integrated in chips).
The function measures multiple temperature points and reports the readout to the master. The measurement of all the enabled
temperature sensors is cyclic and continuous.
Sensor Scan The Control register of the function defines which temperature sensors are included in the scan. A sensor is
scanned only if it is enabled by the Sensor Enable bits (EN0, EN1, and EN2). The sensors are scanned in an ascending, roundrobin order, based on the sensor number. Disabled sensors are skipped and the next enabled sensor in ascending order is scanned.
The minimum scan rate is recommended to be 4Hz (i.e. the measurement data is updated at least once in 250 ms), see Section
2.10 for further details. In Low-Power Mode, the scan rate is four times lower than the scan rate in Active Mode. The scan rate
effects the bus bandwidth required to read the results. The sampling rate of the temperature measurements can also be controlled
via the Conversion Rate register, see Section 2.10 for further details.
Data Readout When a new result is stored in the Readout register a Function Event is generated. Reading the Readout register
clears the Status Function 1 flag (SF1). The result is available in the Readout register waiting for the master to read it during the
master sensor read sequence. If a new result is ready before the previous result has been read, the new result overwrites the
previous result and the Error Function 1 flag (ERF1) is set (indicating an overrun event). Reading the Readout register clears also
the Error Function 1 flag (ERF1). The Readout register contains the temperature data, and the sensor number. Since the LM32
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Readout Resolution The resolution of the readout is defined in the Temperature Capabilities register. The resolution of the
LM32 is fixed and cannot be modified by software. The temperature readout type is common to all the sensors and is signed two's
complement fixed point value. The readout type is specified in the Capabilities register of the function.
Sensor 0 in the Temperature Measurement function is reserved for local temperature measurement (i.e., the junction temperature
of the LM32).
Function Event The Temperature Measurement function generates a Function Event whenever a conversion cycle is completed
and new data is stored in the Readout Register. When the new data is stored into the Readout register the SF1 bit in the device
Status register is set to "1" and remains set, until it is cleared by reading the Readout register. An Attention Request is generated
on the bus, only if it is enabled by the Attention Enable bit (ATE) in the Temperature Control register.
Setup Before Enabling
No setup is required for the Temperature Measurement function before the function is enabled.
2.9.2 Temperature Capabilities (Addr: 001 000; 08h)
Reg
Add
Register
Name
R/
W
001 000 Temperature
Capabilities
P
O
R
Val
Bit
Bit
15
14
MSb
R 0549h
Bit
13
Bit
12
Bit
11
Reserved
0
0
0
Bit
Bit 0
Bit 9 Bit 8 Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1
10
LSb
# of Remotes
0
0
1
0
Int Rout Sign
Sen Size
s
1
0
1
10-Bits
0
0
0.5°C Resolution
1
0
0
1
This register defines the format of the temperature data in the readout register. The LM32 only supports one format for all temperatures as defined by the values of this register.
Bit
Type
2-0
RO
Resolution. This field defines the value of 1 LSb of the Temperature Readout field in the Readout Register.
The SensorPath specification defines many different weights for the temperature LSb. The LM32 supports a
resolution of 0.5 °C and thus a value of 001 for this field. For a full definition of this field, please refer to the
SensorPath specification.
Description
5-3
RO
Number of Bits. This field defines the total number of significant bits of the Temperature Readout field in the
Readout register. The total number of significant bits includes the number of bits representing the integer part
of the temperature data and the fractional part of it, as defined by the Resolution field. The LM32 supports 10bits and thus a value of 001 for this field. For a full definition of this field please refer to the SensorPath
specification.
6
RO
Sign (Signed Data). Defines the type of data in the Temperature Readout field of the Readout register.
0: Unsigned, positive fixed point value.
7
RO
8
RO
1: Signed, 2's complement fixed point value. (value for the LM32)
RoutSize (Readout Register size). Defines the total size of the Readout register.
0: 16 bits. (value for the LM32)
IntSens (Internal Sensor Support). Indicates if the device supports internal temperature measurements, as
the LM32 does.
0: No internal temperature measurement
11-9
RO
15-12
RO
1: Internal temperature sensor implemented. (value for the LM32)
# of Remotes (Number of Remote Sensors). Specifies the number of remote Temperature Sensors supported
by the function.
2: The number of Remote Temperature Sensors. (value for the LM32)
Reserved. Will always read "0".
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LM32
only supports three temperature zones the sensor number field will be zero to two. Other fields in the Readout register as defined
by the SensorPath specification are not supported.
LM32
2.9.3 Temperature Data Readout (Addr: 001 001; 09h)
Reg
Add
Register
Name
R/
W
P
O
R
Val
Local
Temperature
Data
Readout
Bit
Bit
15
14
MSb
Bit
13
Bit
12
Bit
11
Bit
Bit 0
Bit 9 Bit 8 Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1
10
LSb
Reserved
0
001 001 Processor/
Remote
Temperature
Data
Readout
R
MSb 128
Sign °C
64°
C
32°
C
16°
C
8°C
4°C
2°C
1°C
0.5
°C
0
Reserved
0
Reserved
0
SNUM
Res
EF
0
0
0
Bit
Type
Description
0
RO
Reserved. Will always read "0".
1
RO
Reserved for Local Temperature Data Readout. Will always read "0".
EF (Error Flag) for Remote Temperature Data Readout. This bit indicates that an error was detected during
the measurement of the current remote Temperature sensor such as a diode fault condition. When a diode fault
occurs the value of the temperature reading will be 200h or -256°C.
0: No error detected.
1: Error detected.
3-2
RO
SNUM (Sensor Number). This field indicates the number of the current Temperature Sensor, to which the data
in the Temperature Readout field belongs. Temperature Sensor 0 is always assigned to the local sensor of the
LM32.
0: Local temperature sensor (see Thermal Diode Input Mapping)
1-2: Remote sensor 1 and 2 (see Thermal Diode Input Mapping)
5-4
RO
Reserved. Will always read "0".
15-6
RO
Temperature Readout. This field holds the result of the temperature measurement. The active size of this field
for the LM32 is 10-bits, left justified. See Temperature Data Format for examples.
Thermal Diode Input Mapping
Sensor Number
(SNUM)
Sensor Input
0
Local
1
Processor, D1+/D1-
2
Remote, D2+/D2-
Board Connection
none
CPU Thermal Diode
MMBT3904 Thermal Diode or GPU
Thermal Diode
All LM32 temperature data has a common format. The LM32's temperature data format is two's complement and has 10-bits of
resolution with the LSb having a weight of 0.5 °C. The LM32 can resolve temperature between +255.5 °C and -256 °C, inclusive.
It can measure local temperatures between +85 °C and 0 °C and remote temperatures between +125 °C and 0 °C with an accuracy
of ±3.0 °C.
Temperature Data Format
Temperature
Binary
Hex
+140 °C
01 0001 1000
118h
+100 °C
00 1100 1000
0C8h
+1 °C
00 0000 0010
002h
0 °C
00 0000 0000
000h
- 0.5 °C
11 1111 1111
3FFh
-1 °C
11 1111 1110
3FEh
- 40 °C
11 1011 0000
3B0h
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Binary
Hex
-255.5 °C
10 0000 0001
201h
-256 °C
10 0000 0000
200h
LM32
Temperature
2.9.4 Temperature Control (Addr: 001 010; 0Ah)
This register is set to the reset value by a Device Reset.
Reg
Add
Register
Name
R/
W
001 010 Temperature R/
Control
W
P
O
R
Val
Bit
Bit
15
14
MSb
Bit
13
Bit
12
Bit
11
0
0
0
Bit
Bit 0
Bit 9 Bit 8 Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1
10
LSb
0h
Reserved
0
0
0
EN2 EN1 EN0 ATE
0
0
0
0
0
0
Bit
Type
Description
0
R/W
ATE (Attention Enable). When set, this bit enables an Attention Request signal to be generated by the LM32,
if the EN0, EN1 or EN2 bits of this register are set.
0: Attention Request disabled (from enabled Temperature Sensor- default)
1: Attention Request enabled (from enabled Temperature Sensor)
1
R/W
EN0 (Enable Sensor 0). When this bit is set, the Local Temperature Sensor is enabled for temperature
measurements.
0: Temperature Sensor disabled (default)
1: Temperature Sensor enabled
2
R/W
EN1 (Enable Sensor 1). When this bit is set, the Remote Thermal Diode 1 Temperature Sensor is enabled for
temperature measurements.
0: Temperature Sensor disabled (default)
1: Temperature Sensor enabled
3
R/W
EN2 (Enable Sensor 2). When this bit is set, the Remote Thermal Diode 2 Temperature Sensor is enabled for
temperature measurements.
0: Temperature Sensor disabled (default)
1: Temperature Sensor enabled
15-4
RO
Reserved. Will always read "0".
2.10 CONVERSION RATE (Addr: 100 000; 20h)
Reg Add
Register Name
100 000
Conversion Rate
R/
W
P
O
R
Val
R/
W
Bit 7
Bit 6
Bit 5
2h
Bit 4
Bit 3
Bit 2
Reserved
0
0
0
0
0
Bit 1
Bit 0
LSb
CR1
CR0
0
Bit
Type
Description
1-0
RO
CR0 and CR1 (Conversion Rate bits 0 and 1) These bits control the conversion rate of the LM32 for more
details see Conversion Rate Control and desciption below.
7-2
RO
Reserved. Will always read "0".
Conversion Rate Control
LowPwr
[CR1:CR0]
Typical Conversion Rate (ms)
0
00
Fastest*: continuous
1
00
91
0
01
91
1
01
364
0
10
182 (default)
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LM32
LowPwr
[CR1:CR0]
Typical Conversion Rate (ms)
1
10
728
0
11
364
1
11
1456
*Fastest: 2x7.5ms(remote) + 7.5msec (local) = 22.5 ms total
The sensor conversion rate is controlled by this register as well as the Low Power Bit of Device Control Register. This register is
not defined by the SensorPath specification. Therefore, on a motherboard when using a Super I/O host this register must be
modified during BIOS run time. The conversion rate is dependent on system physical requirements and limitations. The thermal
response time of the MSOP package is one such requirement. Most systems will function properly with the default settings. The
master scan rate is related to the conversion rate of the LM32. If attentions are enabled the conversion rate and scan rate will be
equal.
A diode connected 2N3904 approximates the junction available on a Pentium microprocessor for temperature measurement. Therefore, the LM32 can sense the temperature of this
diode effectively. Although, an offset will be observed. The
temperature reading will be offset by approximately −4.5°C,
therefore a correction factor of +4.5°C should be added to all
temperature readings when using a 2N3904 transistor.
3.0 Application Hints
The LM32 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 LM32'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 LM32 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 LM32'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 LM32's temperature. The LM32 has been optimized to measure the remote diode of a 90 nm Pentium 4
processor as shown in Figure 7. 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.
3.1 DIODE NON-IDEALITY
3.1.1 Diode Non-Ideality Factor Effect on Accuracy
When a transistor is connected as a diode, the following relationship holds for variables VBE, T and If:
where:
•
•
•
•
q = 1.6×10−19 Coulombs (the electron charge),
T = Absolute Temperature in Kelvin
k = 1.38×10−23joules/K (Boltzmann's constant),
η is the non-ideality factor of the process the diode is
manufactured on,
• IS = Saturation Current and is process dependent,
• If= Forward Current through the base emitter junction
• VBE = Base Emitter Voltage drop
In the active region, the -1 term is negligible and may be eliminated, yielding the following equation
In the above equation, η and IS are dependant upon the process that was used in the fabrication of the particular diode.
By forcing two currents with a very controlled ration (N) and
measuring the resulting voltage difference, it is possible to
eliminate the IS term. Solving for the forward voltage difference yields the relationship:
20071115
FIGURE 7. 90 nm Pentium 4 Temperature vs LM32
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.
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The non-ideality factor, η, is the only other parameter not accounted for and depends on the diode that is used for measurement. Since ΔVBE is proportional to both η and T, the
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sure is in microvolts. The following guidelines should be followed:
1. Place the 100 pF and 0.1 µF power supply bypass
capacitors as close as possible to the LM32's power pin.
Place the recommended thermal diode 100 pF capacitor
as close as possible to the LM32's D+ and D− pins. Make
sure the traces to the thermal diode 100 pF capacitor are
matched.
2. The recommended 100 pF diode capacitor actually has
a range of 0 pF to 3.3 nF (see curve in Typical
Performance Characteristics for effect on accuracy). 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 LM32 should be placed within 10cm of the
Processor diode pins with the traces being as straight,
short and identical as possible. Trace resistance of
0.7Ω can cause as much as 1°C of error. This error can
be compensated for by adding or subtracting an offset to
the remote temperature reading(s).
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.
5. Avoid routing diode traces in close proximity to power
supply switching 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 LM32'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. Seventeen nano-amperes of leakage can
cause as much as 0.2°C of error in the diode temperature
reading (see curve in Typical Performance
Characteristics). Keeping the printed circuit board as
clean as possible will minimize leakage current.
The SensorPath Bus is less sensitive to noise than its predecessor the SMBus due to the inherent filtering present in the
pulse-width encoding of the data. Care still needs to be taken
such that induced noise is analyzed and minimized. SensorPath Bus corrupt data is the most common symptom for noise
coupled in SWD. A no-ACK is the symptom for noise coupled
into the Device Number Select pin (ADD). An RC lowpass
filter as well as a debouncing circuit are included in the LM32
that filter noise spikes less than 2.5 µsec in duration on the
SWD signal.
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. The
following table shows the variations in non-ideality for a variety of processors.
η, non-ideality
Processor Family
min
typ
max
Pentium II
1
1.0065 1.0173
Pentium III CPUID 67h
1
1.0065 1.0125
Pentium III CPUID 68h/ 1.0057
PGA370Socket/Celeron
1.008
Series
R
1.0125
Pentium 4, 423 pin
0.9933 1.0045 1.0368
Pentium 4, 478 pin
0.9933 1.0045 1.0368
Pentium 4 on 0.13
micron process,
2-3.06GHz
1.0011 1.0021 1.0030 3.64 Ω
Pentium 4 on 90 nm
process
Pentium M Processor
(Centrino)
3.33 Ω
1.011
1.0015 1.0022 1.0028 3.06 Ω
1
0
9
MMBT3904
1.003
AMD Athlon MP model 6 1.002
1.008
1.016
3.2 PCB LAYOUT for MINIMIZING NOISE
20071117
FIGURE 8. Ideal Diode Trace Layout
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 LM32 can cause temperature conversion errors.
Keep in mind that the signal level the LM32 is trying to mea-
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LM32
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 III 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:
LM32
Physical Dimensions inches (millimeters) unless otherwise noted
14-Lead Molded Thin Shrink Small Outline Package (TSSOP,
JEDEC Registration Number MO-153 Variation AB Ref Note 6 dated 7/93,
Order Number LM32CIMT, or LM32CIMTX,
NS Package Number MTC14C
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LM32
Notes
23
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LM32 Dual Thermal Diode Temperature Sensor with Bus
Notes
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