For RTOHB: Remote Temperature Offset High Byte. Power up default is LHIGH = RHIGH = 0˚C. 1 LSB = 1˚C. Two’s complement

format.

(Read/Write Address 12h):

BIT

D7

D6

D5

D4

D3

D2

D1

D0

Value

0.5

0.25

0.125

0000

0

For RTOLB: Remote Temperature Offset High Byte. Power up default is 0˚C. 1 LSB = 0.125˚C. Two’s complement format.

The offset value written to these registers will automatically be added to or subtracted from the remote temperature measurement

that will be reported in the Remote Temperature registers.

2.9 LOCAL and REMOTE T_CRIT REGISTERS (RCS and LCS)

(Read/Write Address 20h, 19h):

BIT

D7

D6

D5

D4

D3

D2

D1

D0

Value

SIGN

64

32

16

8

4

2

1

D7–D0: T_CRIT setpoint temperature data. Power up default is Local T_CRIT = 85˚C and Remote T_CRIT=110˚C. 1 LSB = 1˚C,

two’s complement format.

2.10 T_CRIT HYSTERESIS REGISTER (TH)

(Read and Write Address 21h):

BIT

D7

D6

D5

D4

D3

D2

D1

D0

Value

16

842

1

D7–D0: T_CRIT Hysteresis temperature. Power up default is TH = 10˚C. 1 LSB = 1˚C, maximum value = 31.

2.11 FILTER and ALERT CONFIGURE REGISTER

(Read and Write Address BFh):

BIT

D7

D6

D5

D4

D3

D2

D1

D0

Value

00000

Filter Level

ALERT

Configure

D7-D3: is not defined defaults to "0".

D2-D1: input filter setting as defined the table below:

D2

D1

Filter Level

0

0

No Filter

0

1

Level 1

1

0

Level 1

1

1

Level 2

Level 2 sets maximum filtering.

D0: when set to "1" comparator mode is enabled.

2.12 MANUFACTURERS ID REGISTER

(Read Address FEh) The default value is 01h.

2.13 DIE REVISION CODE REGISTER

(Read Address FFh) The LM89 version has a default value of 31h or 49 decimal. The LM89-1 version has a default value of 34h

or 52 decimal. This register will increment by 1 every time there is a revision to the die by National Semiconductor.

3.0 Applications Hints

The LM89 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 LM89’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 LM89 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 LM89’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 LM89’s temperature. The LM89 has been

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