Rainbow Electronics LM88 User Manual

August 2001

LM88
Factory Programmable Dual Remote-Diode Thermostat

LM88 Factory Programmable Dual Remote-Diode Thermostat

General Description

The LM88 is a dual remote-diode temperature sensor with 3
digital comparators. The LM88 has 3 open-drain outputs
(O_SP0, O_SP1 and O_CRIT) that can be used as inter­rupts or to signal system shutdown. The digital comparators
can be factory programmed to make a greater than or less
than comparison. When programmed for a greater than
comparison outputs:

O_SP0 and O_SP1 activate when the temperatures mea­sured by D0 or D1 exceed the associated setpoints of
T_SP0 or T_SP1.

O_CRIT activates when the temperature measured by
either D0 or D1 exceeds setpoint T_CRIT.

T_CRIT can be set at 1˚C intervals from −40˚C to +125˚C.
T_SP0 andT_SP1 can be set at 4˚C intervals in the range of
T_CRIT +127˚C/−128˚C. Hysteresis for all comparators is
set to 1˚C. O_CRIT, in conjunction with T_CRIT, could be
used to prevent catastrophic damage to key subsystems
such as notebook Card Bus cards while O_SP0 and O_SP1,
in conjunction with T_SP0 and T_SP1, can warn of an
impending failure.

The LM88 is available in an 8-lead mini-small-outline pack­age.

Applications

n Microprocessor Thermal Management
n Appliances
n Portable Battery Powered Systems
n Fan Control
n Industrial Process Control
n HVAC Systems
n Remote Temperature Sensing
n Electronic System Protection

Features

n 2 external remote diode input channels
n 3 digital comparator outputs, 1 per remote diode and

one T_CRIT common to both

n Factory programmable greater than or less than

comparisons

n 1˚C comparator hysteresis
n 2 setpoints, T_SP0 and T_SP1, factory programmable in

4˚C intervals

n 1 setpoint, T_CRIT, factory programmable in 1˚C

intervals

n Active Low open-drain digital outputs
n 8-pin mini-SO plastic package

Key Specifications

j

Power Supply Voltage 2.8V–3.8V

j

Power Supply Current 1.5 mA (max)

j

LM88 Temperature Range −40˚C to +85˚C

j

Diode Setpoint Temperature

Range 0˚C to +125˚C

j

Temperature Trip PointAccuracy:

Diode Junction

Temperature

)

(T

DJ

+45˚C to +85˚C
+60˚C to +100˚C

Note: These are sample ranges. Contact factory for other

ranges.

LM88CIM
Accuracy

±

3˚C (max) −40˚C to +85˚C

±

3˚C (max) −40˚C to +85˚C

LM88CIM

Temperature

Range

Simplified Block Diagram and Connection Diagram

MSOP-8/MUA08A Package

Top View

10132601

© 2001 National Semiconductor Corporation DS101326 www.national.com

For simplicity, the effects of the hysteresis are not shown in the
temperature response diagram.

10132602

Simplified Block Diagram and Connection Diagram (Continued)

LM88

Order Number Device

Marking

LM88CIMM-A
LM88CIMMX-A Tape and

LM88CIMM-B
LM88CIMMX-B Tape and

For other setpoints please contact the factory. Performance is dependent on temperature range.

T08A

T08A

NS Package

Number

MUA08A

or

MSOP-8

MUA08A

or

MSOP-8

Transport

Media

Rail

Real

Rail

Real

T_SP0

(˚C)

61 49 80

41 49 60

Typical Application

T_SP1

(˚C)

T_CRIT

(˚C)

S etpoint

Accuracy

(˚C)

±

3

±

3

FIGURE 1. Thermal Protection for Pentium®Processor and Graphics Chip

10132613

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LM88

Absolute Maximum Ratings (Note 1)

Input Voltage 6V
Input Current at any pin (Note 2) 5mA
Package Input Current (Note 2) 20mA
Package Dissipation at T

(Note 4) 900mW

Soldering Information

MSOP Package (Note 6) :

= 25˚C

A

Operating Ratings(Note 1)

Operating Temperature
Range T

LM88CIMM −40˚C ≤ TA≤ +85˚C

Remote Diode Junction 0˚C ≤ T
Positive Supply Voltage (V
Maximum V

and V

O_CRIT,VO_SP0

O_SP1

+

) +2.8V to +3.8V

MIN

≤ T ≤ T

≤ +125˚C

DJ

Vapor Phase (60 seconds) 215˚C
Infrared (15 seconds) 220˚C

Storage Temperature −65˚C to + 150˚C
ESD Susceptibility (Note 5)

Human Body Model
Machine Model

2500V
250V

LM88 Electrical Characteristics

The following specifications apply for 2.8VDC≤V+≤ 3.8VDCunless otherwise specified. Boldface limits apply for TA=TJ=
T

to T

MIN

Symbol Parameter Conditions (Note 7) Limits (Limits)

Temperature Sensor

V

D−,VD0

I

D+SOURCE

V

D−Out

; all other limits TA=TJ= 25˚C unless otherwise specified.

MAX

Typical LM88CIMM Units

(Note 8)

Setpoint Temperature Accuracy (Note 9) +60˚C ≤ T

+45˚C ≤ T
+30˚C ≤ T

≤ +100˚C

DJ

≤ +85˚C

DJ

≤ +70˚C

DJ

±

3 ˚C (max)

Setpoint Hysteresis 1 ˚C (min)

1 ˚C (max)

Output Update Rate 920 ms (max)

and VD1Analog Inputs

Diode Source Current (D+ − D−)=0.65; high

level
(D+ − D−)=0.65; low

level

120 210 µA (max)

46 µA (min)

12 21 µA (max)

4.6 µA (min)

D− Output Source Voltage 0.7 V

MAX

+5.5V

LM88 Electrical Characteristics

The following specifications apply for 2.8VDC≤V+≤ 3.8VDCunless otherwise specified. Boldface limits apply for TA=TJ=
T

to T

MIN

Symbol Parameter Conditions Typical Limits Units

+

V

Power Supply

Digital Outputs

I

OUT(“1”)

V

OUT(“0”)

Note 1: Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating Ratings indicate conditions for which the device is
functional, but do not guarantee specific performance limits. For guaranteed specifications and test conditions, see the Electrical Characteristics. The guaranteed
specifications apply only for the test conditions listed. Some performance characteristics may degrade when the device is not operated under the listed test
conditions.

; all other limits TA=TJ= 25˚C unless otherwise specified.

MAX

I

S

Supply Current 1.5 mA (max)

Logical “1” Output Leakage
Current (Note 10)

V
where V

2.8V
V

2.8V

Logical “0” Output Voltage I

(Note 7) (Note 8) (Limits)

=V+− 0.6V

OUT

+

=3.8V to

=V+=3.8V to

OUT

=+3mA 0.4 V (max)

OUT

2 µA (max)

40 µA (max)

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LM88 Electrical Characteristics (Continued)

LM88

Note 2: When the input voltage (VI) at any pin exceeds the power supply (V

maximum package input current rating limits the number of pins that can safely exceed the power supplies with an input current of 5mA to four.
Note 3: Parasitics or ESD protectioncircuitryareshownin the diagram found below.The ESD Clamp circtuitry is triggered on when there is an ESD event. The table

maps what devices appear on the different pins.

<

I

GND or V

>

V+), the current at that pin should be limited to 5mA. The 20mA

I

Pin Name D1 D2 D3 D4 D5 D6 R1
D0+ XXXX X50Ω
D− XXXXXX50Ω
D1+ XXXX X50Ω
O_CRIT
O_SP1
O_SP0

XXXX 0Ω
XXXX 0Ω
XXXX 0Ω

10132604

Note 4: The maximum power dissipation must be derated at elevated temperatures and is dictated by T
ambient thermal resistance) and T
given in the Absolute Maximum Ratings, whichever is lower. For this device, T
package types when board mounted follow:

(ambient temperature). The maximum allowable power dissipation at any temperature is PD=(T

A

Package Type θ

= 125˚C. For this device the typical thermal resistance (θJA) of the different

Jmax

JA

(maximum junction temperature), θJA(junction to

Jmax

)/θJAor the number

Jmax–TA

MUA08A 250˚C/W

Note 5: The human body model is a 100pF capacitor discharged through a 1.5kΩ resistor into each pin. The machine model is a 200pF capacitor discharged directly
into each pin.

Note 6: See the URL ”http://www.national.com/packaging/“ for other recomdations and methods of soldering surface mount devices.
Note 7: Typicals are at T
Note 8: Limits are guaranteed to National’s AOQL (Average Outgoing Quality Level).
Note 9: These are sample temperature ranges, contact the factory for other temperature ranges. Performance is dependent on temperature range.
Note 10: The two I

current, 2µA (max). In Region 2, V
current flow is under short circuit conditions as specified at 40µA (max). Under normal operating conditions a pull-resistor (R) will be used. The voltage drop across
this pull-up resistor caused by the 2µA normal leakage current with large values of R (much greater than 100k) will bias diode D1 into the cutoff region causing the
additional current to be negligible in the voltage drop calculation. With low values of R more current will flow as in the case of a 1.1k pull-up, 20µA may flow causing
less than 22mV of voltage drop.

specifications are intended to describe two operating regions of the output voltage. In Region 1, V+− 0.6V and below, there is normal leakage

OH

= 25˚C and represent most likely parametric norm.

J=TA

+

− 0.6V to V+, there is additional current flowing caused by the ESD protection circuitry (see Figure in Note 3). The maximum

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1.0 Functional Description

LM88

a) When programmed for a greater than comparison

10132611

FIGURE 2. Comparator output temperature response diagrams

1.1 PIN DESCRIPTIONS

+

V

This is the positive supply voltage pin, which has
a range of 2.8 to 3.8 volts. This pin should be

bypassed with a 0.1µF capacitor to ground.
GND This is the ground pin.
D0+, D1+ These pins connect to the positive terminal of the

diodes (e.g. a 2N3904 collector base shorted or a

Pentium thermal diode anode) and provide the

source current for forward biasing the diodes for

the temperature measurement. During a tem-

perature conversion, the current source switches

between 120µA and 12µA. The diodes are

sampled sequentially.
D− This pin should be connected to the negative pin

of each diode (e.g. a 2N3904 emitter or a Pen-

tium thermal diode cathode). A star connection is

recommended. Separate traces should be routed

from this pin to each diode cathode. This pin

biases the negative diode terminals to approxi-

mately 0.7V.
O_CRIT

This is an active-low open-drain digital output. It

goes LOW when a comparison of either diode

temperature reading to the setpoint T_CRIT is

true. It returns to HIGH when the comparison of

the diode temperature, that caused the true con-

b) When programmed for a less than comparison

±

dition, to T_CRIT

1˚C is false. The CRIT com­parator can be factory programmed to make a
greater than or less than comparison. (See Sec­tion 1.3 LM88 OPTIONS)

O_SP1

This is an active-low open-drain digital output. It
goes LOW when the comparison of the tempera­ture reading of diode one to the value of T_SP1 is
true. The SP1 comparator has a built in hyster­esis of 1˚C. Therefore, O_SP1 returns to HIGH
when diode one’s temperature comparison to the
value of T_SP1

±

1˚C is false. The SP1 compara­tor can be factory programmed to make a greater
than or less than comparison.(See Section 1.3
LM88 OPTIONS)

O_SP0

This is an active-low open-drain digital output. It
goes LOW when the comparison of the tempera­ture reading of diode one to the value of T_SP0 is
true. The SP0 comparator has a built in hyster­esis of 1˚C. Therefore, O_SP0 returns to HIGH
when diode one’s temperature comparison to the
value of T_SP0

±

1˚C is false. The SP0 compara­tor can be factory programmed to make a greater
than or less than comparison.(See Section 1.3
LM88 OPTIONS)

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1.0 Functional Description (Continued)

LM88

1.2 TYPICAL PIN CONNECTION

Pin Label Pin Number Typical Connection
D0+ 1 3904-type transistor

D− 2 3904-type transistor emitter or

D1+ 3 3904-type transistor shorted

GND 4 a quiet system ground
O_CRIT

O_SP1

O_SP1

+

V

shorted-collector base or
Pentium thermal diode anode;

2.2nF capacitor connected to
D-

Pentium thermal diode
cathode (individual traces are
required to each diode; do not
daisy chain); two 2.2nF
capacitors connected to D0+
and D1+

collector-base or Pentium
thermal diode anode; 2.2nF
capacitor connected to D-

5 2k pull-up; system shutdown

or the THERM pin of the ICH
(I/O Controller Hub found in
PCs)

6 2k pull-up; general purpose

input (GPI), to determine
which diode caused the
THERM event

7 2k pull-up; general purpose

input (GPI), to determine
which diode caused the
THERM event

8 3.3V; 0.1µF bypass capacitor

1.3 LM88 OPTIONS

1.3.1 Set-Point Values

T_SP0 and T_SP1 are dependent on the value of T_CRIT:

T_SP0 = T_CRIT + 4a + 1

T_SP1 = T_CRIT + 4b + 1
where:
a and b are any integer in the range of −32 to +31.
T_CRIT can be any value in the range of 0˚C to +125˚C with

a resolution of 1˚C.

1.3.2 Functionality

The LM88’s comparators can be factory programmed to do a
greater than or less than comparison. When programmed for
a greater than comparison, the comparison result is true
when the temperature measured is above the prepro­grammed setpoint temperature. The comparison returns to
false when the temperature measured is below or equal to
the setpoint temperature minus one degree. For a less than
comparison the comparison result is true when the tempera­ture measured is below the preprogrammed limit. The result
turns to false when the temperature measured is above or
equal to the setpoint limit plus one degree. SP0, SP1 and
CRIT comparisons can all be independently programmed to

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be greater than or less than. All CRIT comparisons are
required to be the same, either greater than or less than. The
comparator hysteresis can also be factory set to one, two or
three degrees. The hysteresis for all comparisons is required
to be the same.

2.0 Application Hints

2.1 OPEN-DRAIN OUTPUTS

The O_SP0, O_SP1 and 0_CRIT 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 LM88. The maximum
resistance of the pull-up needed to provide a 2.1V high level,
based on LM88 specification for High Level Output Current
with the supply voltage at 3.0V, is 430kΩ.

2.2 THERMAL DIODE MOUNTING CONSIDERATIONS

To measure temperature the LM88 uses two remote diodes.
These diodes can be located on the die of a target IC,
allowing measurement of the IC’s temperature, independent

2.0 Application Hints (Continued)

of the LM88’s temperature. The LM88 has been optimized to
measure the remote diode of a Pentium type processor as
shown in
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.

As with any IC, the LM88 and accompanying wiring and
circuits must be kept insulated and dry, to avoid leakage and
corrosion. This is especially true if the circuit may operate at
cold temperatures where condensation can occur.
Printed-circuit coatings and varnishes such as Humiseal and
epoxy paints or dips are often used to ensure that moisture
cannot corrode the LM88 or its connections. Moisture may
also cause leakage on the diode wiring and therefore affect
the accuracy of the temperature set-points.

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 III microprocessor for temperature mea­surement. Therefore, the LM88 can sense the temperature
of this diode effectively.

2.3 EFFECTS OF THE DIODE NON-IDEALITY FACTOR ON ACCURACY

The technique used in today’s remote temperature sensors
is to measure the change in V
points of a diode. For a bias current ratio of N:1, this differ­ence is given as:

where:

The temperature sensor then measures ∆V
to IT digital data. In this equation, k and q are well defined
universal constants, and N is a parameter controlled by the

Figure 3

. A discrete diode can also be used to

10132615

FIGURE 3. Pentium or 3904 Temperature vs LM88

Temperature Set-point

at two different operating

BE

— 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.

and converts

BE

temperature sensor. The only other parameter is η, which
depends on the diode that is used for measurement. Since

is proportional to both η and T, the variations in η

∆V

BE

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:

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.

2.4 PCB LAYOUT to MINIMIZE NOISE

In a noisy environment, such as a processor motherboard,
layout considerations are very critical. Noise induced on
traces running between the remote temperature diode sen­sor and the LM88 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

DD

capacitor as close as possible to the D+ and D− pins.
Make sure the traces to the two 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 change over that capacitance
range. Increasing the capacitance will lower the corner
frequency where differential noise error will start to affect
the temperature reading thus producing a reading that is
more stable. Conversely, lowering the capacitance will
increase the corner frequency where differential noise
error starts to affect the temperature reading thus pro­ducing a reading that is less stable.

3. Ideally, the LM88 should be placed within 10cm of the

remote 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. This error can be com­pensated by using the Remote Temperature Offset Reg­isters, since the value placed in these registers will
automatically be subtracted or added to the remote tem­perature reading.

4. Diode traces should be surrounded by a GND guard ring

to either side, above and below if possible. This GND
guard should not go between the D+ and D− lines so
that in the event that noise does couple to the diode
lines, it would be coupled common mode and rejected­.(See

Figure 4

)

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.

LM88

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2.0 Application Hints (Continued)

LM88

8. The ideal place to connect the LM88’s GND pin is as
close as possible to the processor 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

FIGURE 4. Ideal Diode Trace Layout

3.0 Applications Circuits

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.

10132633

FIGURE 5. Pentium processor Thermal Management with Fan Control

FIGURE 6. Card Bus Thermal Management

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10132614

10132603

Physical Dimensions inches (millimeters)

unless otherwise noted

LM88 Factory Programmable Dual Remote-Diode Thermostat

8-Lead Molded Mini Small Outline Package (MSOP)

(JEDEC REGISTRATION NUMBER M0-187)
Order Number LM88CIMM, or LM88CIMMX

NS Package Number MUA08A

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COUNSEL OF NATIONAL SEMICONDUCTOR CORPORATION. As used herein:

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whose failure to perform when properly used in
accordance with instructions for use provided in the

2. A critical component is any component of a life
support device or system whose failure to perform
can be reasonably expected to cause the failure of
the life support device or system, or to affect its
safety or effectiveness.

labeling, can be reasonably expected to result in a
significant injury to the user.

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National does not assume any responsibility for use of any circuitry described, no circuit patent licenses are implied and National reserves the right at any time without notice to change said circuitry and specifications.