LM88 datasheet(6/9 Pages) NSC

6 / 9 page

1.0 Functional Description (Continued)

1.2 TYPICAL PIN CONNECTION

Pin Label

Pin Number

Typical Connection

D0+

3904-type transistor

shorted-collector base or

Pentium thermal diode anode;

2.2nF capacitor connected to

D-

D−

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+

3904-type transistor shorted

collector-base or Pentium

thermal diode anode; 2.2nF

capacitor connected to D-

GND

a quiet system ground

O_CRIT

2k pull-up; system shutdown

or the THERM pin of the ICH

(I/O Controller Hub found in

PCs)

O_SP1

2k pull-up; general purpose

input (GPI), to determine

which diode caused the

THERM event

O_SP1

2k pull-up; general purpose

input (GPI), to determine

which diode caused the

THERM event

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 430k

Ω.

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

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