LM90

SNIS126A – MAY 2004 – REVISED MARCH 2013

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D7–D0: T_CRIT setpoint temperature data. Power up default is T_CRIT = 85°C. 1 LSB = 1°C, two's complement

format.

T_CRIT HYSTERESIS REGISTER (TH)

Table 13. T_CRIT HYSTERESIS REGISTER (TH) (Read and Write Address 21h):

BIT

D7

D6

D5

D4

D3

D2

D1

D0

Value

16

8

4

2

1

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

FILTER and ALERT CONFIGURE REGISTER

Table 14. FILTER and ALERT CONFIGURE REGISTER (Read and Write Address BFh):

BIT

D7

D6

D5

D4

D3

D2

D1

D0

Value

0

0

0

0

0

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.

MANUFACTURERS ID REGISTER

(Read Address FEh) Default value 01h.

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.

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 15. 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 affected, and often dominated, by the temperature of its leads.

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