For RTOHB: Remote Temperature Offset High Byte. Power up default is LHIGH = RHIGH = 0˚C. 1LSB = 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. 1LSB = 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 T_CRIT = 85˚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) Default value 01h.

2.13 DIE REVISION CODE REGISTER

(Read Address FFh) Default value 21h. This register will increment by 1 every time there is a revision to the die by National

Semiconductor.

4.0 Application Hints

The LM90 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 LM90’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

LM90 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 LM90’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 LM90’s temperature. The LM90 has been

optimized to measure the remote diode of a Pentium III

processor as shown in

Figure 11. A discrete diode can also

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