LM88CIMM-B - National Semiconductor

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 inter-

rupts 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 mea-

sured 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 and T_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 pack-

age.

Applications

nMicroprocessor Thermal Management

nAppliances

nPortable Battery Powered Systems

nFan Control

nIndustrial Process Control

nHVAC Systems

nRemote Temperature Sensing

nElectronic System Protection

Features

n2 external remote diode input channels

n3 digital comparator outputs, 1 per remote diode and

one T_CRIT common to both

nFactory programmable greater than or less than

comparisons

n1˚C comparator hysteresis

n2 setpoints, T_SP0 and T_SP1, factory programmable in

4˚C intervals

n1 setpoint, T_CRIT, factory programmable in 1˚C

intervals

nActive Low open-drain digital outputs

n8-pin mini-SO plastic package

Key Specifications

jPower Supply Voltage 2.8V–3.8V

jPower Supply Current 1.5 mA (max)

jLM88 Temperature Range −40˚C to +85˚C

jDiode Setpoint Temperature

Range 0˚C to +125˚C

jTemperature Trip Point Accuracy:

Diode Junction

Temperature

)

LM88CIM

Accuracy LM88CIM

Temperature

Range

+45˚C to +85˚C ±3˚C (max) −40˚C to +85˚C

+60˚C to +100˚C ±3˚C (max) −40˚C to +85˚C

Note: These are sample ranges. Contact factory for other

ranges.

Simplified Block Diagram and Connection Diagram

MSOP-8/MUA08A Package

10132601

Top View 10132602

For simplicity, the effects of the hysteresis are not shown in the

temperature response diagram.

August 2001

LM88 Factory Programmable Dual Remote-Diode Thermostat

Simplified Block Diagram and Connection Diagram (Continued)

Order Number Device

Marking NS Package

Number Transport

Media T_SP0

(˚C) T_SP1

(˚C) T_CRIT

(˚C) S etpoint

Accuracy

(˚C)

LM88CIMM-A T08A MUA08A

MSOP-8

Rail 61 49 80 ±3

LM88CIMMX-A Tape and

Real

LM88CIMM-B T08A MUA08A

MSOP-8

Rail 41 49 60 ±3

LM88CIMMX-B Tape and

Real

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

Typical Application

10132613

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

LM88

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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

= 25˚C

(Note 4) 900mW

Soldering Information

MSOP Package (Note 6) :

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

Operating Ratings(Note 1)

Operating Temperature

Range T

MIN

≤T≤T

MAX

LM88CIMM −40˚C ≤T

≤+85˚C

Remote Diode Junction 0˚C ≤T

≤+125˚C

Positive Supply Voltage (V

) +2.8V to +3.8V

Maximum V

O_CRIT

O_SP0

and V

O_SP1

+5.5V

LM88 Electrical Characteristics

The following specifications apply for 2.8V

≤V

≤3.8V

unless otherwise specified. Boldface limits apply for T

MIN

to T

MAX

;all other limits T

= 25˚C unless otherwise specified.

Typical LM88CIMM Units

Symbol Parameter Conditions (Note 7) Limits (Limits)

(Note 8)

Temperature Sensor

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

≤+100˚C ±3˚C (max)

+45˚C ≤T

≤+85˚C

+30˚C ≤T

≤+70˚C

Setpoint Hysteresis 1 ˚C (min)

1 ˚C (max)

Output Update Rate 920 ms (max)

D−

and V

Analog Inputs

D+SOURCE

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

level 120 210 µA (max)

46 µA (min)

(D+ − D−)=0.65; low

level 12 21 µA (max)

4.6 µA (min)

D−Out

D− Output Source Voltage 0.7 V

LM88 Electrical Characteristics

The following specifications apply for 2.8V

≤V

≤3.8V

unless otherwise specified. Boldface limits apply for T

MIN

to T

MAX

;all other limits T

= 25˚C unless otherwise specified.

Symbol Parameter Conditions Typical Limits Units

(Note 7) (Note 8) (Limits)

Power Supply

Supply Current 1.5 mA (max)

Digital Outputs

OUT(“1”)

Logical “1” Output Leakage

Current (Note 10) V

OUT

− 0.6V

where V

=3.8V to

2.8V 2µA (max)

OUT

=3.8V to

2.8V 40 µA (max)

OUT(“0”)

Logical “0” Output Voltage I

OUT

=+3mA 0.4 V (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 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.

LM88

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LM88 Electrical Characteristics (Continued)

Note 2: When the input voltage (VI) at any pin exceeds the power supply (VI<GND or VI>V+), the current at that pin should be limited to 5mA. The 20mA

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 protection circuitry are shown in 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.

Pin Name D1 D2 D3 D4 D5 D6 R1

D0+ XXXX X50Ω

D− XXXXXX50Ω

D1+ XXXX X50Ω

O_CRIT XXXX 0Ω

O_SP1 XXXX 0Ω

O_SP0 XXXX 0Ω

10132604

Note 4: The maximum power dissipation must be derated at elevated temperatures and is dictated by TJmax (maximum junction temperature), θJA (junction to

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

Jmax–TA)/θJA or the number

given in the Absolute Maximum Ratings, whichever is lower. For this device, TJmax = 125˚C. For this device the typical thermal resistance (θJA) of the different

package types when board mounted follow:

Package Type θ

MUA08A 250˚C/W

Note 5: The human body model is a 100pF capacitor discharged through a 1.5kΩresistor 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 TJ=T

A= 25˚C and represent most likely parametric norm.

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

current, 2µA (max). In Region 2, V+− 0.6V to V+, there is additional current flowing caused by the ESD protection circuitry (see Figure in Note 3). The maximum

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.

LM88

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1.0 Functional Description

1.1 PIN DESCRIPTIONS

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-

dition, to T_CRIT±1˚C is false. The CRIT com-

parator can be factory programmed to make a

greater than or less than comparison. (See Sec-

tion 1.3 LM88 OPTIONS)

O_SP1 This is an active-low open-drain digital output. It

goes LOW when the comparison of the tempera-

ture reading of diode one to the value of T_SP1 is

true. The SP1 comparator has a built in hyster-

esis 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 compara-

tor 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 tempera-

ture reading of diode one to the value of T_SP0 is

true. The SP0 comparator has a built in hyster-

esis 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 compara-

tor can be factory programmed to make a greater

than or less than comparison.(See Section 1.3

LM88 OPTIONS)

10132611

a) When programmed for a greater than comparison 10132612

b) When programmed for a less than comparison

FIGURE 2. Comparator output temperature response diagrams

LM88

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1.0 Functional Description (Continued)

1.2 TYPICAL PIN CONNECTION

Pin Label Pin Number Typical Connection

D0+ 1 3904-type transistor

shorted-collector base or

Pentium thermal diode anode;

2.2nF capacitor connected to

D-

D− 2 3904-type transistor emitter or

Pentium thermal diode

cathode (individual traces are

required to each diode; do not

daisy chain); two 2.2nF

capacitors connected to D0+

and D1+

D1+ 3 3904-type transistor shorted

collector-base or Pentium

thermal diode anode; 2.2nF

capacitor connected to D-

GND 4 a quiet system ground

O_CRIT 5 2k pull-up; system shutdown

or the THERM pin of the ICH

(I/O Controller Hub found in

PCs)

O_SP1 6 2k pull-up; general purpose

input (GPI), to determine

which diode caused the

THERM event

O_SP1 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 prepro-

grammed 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 tempera-

ture 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

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 pro-

vided 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

LM88

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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

Figure 3

. 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 af-

fected, 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 avail-

able on a Pentium III microprocessor for temperature mea-

surement. 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

at two different operating

points of a diode. For a bias current ratio of N:1, this differ-

ence is given as:

where:

—ηis the non-ideality factor of the process the diode is

manufactured on,

— q is the electron charge,

— k is the Boltzmann’s constant,

— N is the current ratio,

— T is the absolute temperature in ˚K.

The temperature sensor then measures ∆V

and converts

to IT digital data. In this equation, k and q are well defined

universal constants, and N is a parameter controlled by the

temperature sensor. The only other parameter is η, which

depends on the diode that is used for measurement. Since

∆V

is proportional to both ηand T, the variations in η

cannot be distinguished from variations in temperature.

Since the non-ideality factor is not controlled by the tempera-

ture sensor, it will directly add to the inaccuracy of the

sensor. For the Pentium II, Intel specifies a ±1% variation in

ηfrom 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

ACC

=±3˚C+(

1% of 298 ˚K) = ±6˚C

The additional inaccuracy in the temperature measurement

caused by ηcan 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 sen-

sor 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

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 tem-

perature 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 pro-

ducing 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 1Ωcan

cause as much as 1˚C of error. This error can be com-

pensated by using the Remote Temperature Offset Reg-

isters, since the value placed in these registers will

automatically be subtracted or added to the remote tem-

perature 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.

10132615

FIGURE 3. Pentium or 3904 Temperature vs LM88

Temperature Set-point

LM88

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2.0 Application Hints (Continued)

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

as much as 1˚C of error in the diode temperature read-

ing. Keeping the printed circuit board as clean as pos-

sible will minimize leakage current.

3.0 Applications Circuits

10132633

FIGURE 4. Ideal Diode Trace Layout

10132614

FIGURE 5. Pentium processor Thermal Management with Fan Control

10132603

FIGURE 6. Card Bus Thermal Management

LM88

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Physical Dimensions inches (millimeters)

unless otherwise noted

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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whose failure to perform when properly used in

accordance with instructions for use provided in the

labeling, can be reasonably expected to result in a

significant injury to the user.

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.

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LM88 Factory Programmable Dual Remote-Diode Thermostat

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.