EMC1402 datasheet(21/37 Pages) SMSC

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1°C Temperature Sensor with Beta Compensation

Datasheet

SMSC EMC1402

Revision 1.16 (03-15-07)

DATASHEET

5.10

Temperature Monitors

In general, thermal diode temperature measurements are based on the change in forward bias voltage

of a diode when operated at two different currents. This

ΔV

BE is proportional to absolute temperature

as shown in the following equation:

Figure 5.4 shows a block diagram of the temperature measurement circuit. The negative terminal for

the remote temperature diode, DN, is internally biased with a forward diode voltage referenced to

ground.

5.11

Temperature Measurement Results and Data

The temperature measurement results are stored in the internal and external temperature registers.

These are then compared with the values stored in the high and low limit registers. Both external and

internal temperature measurements are stored in 11-bit format with the eight (8) most significant bits

stored in a high byte register and the three (3) least significant bits stored in the three (3) MSB

positions of the low byte register. All other bits of the low byte register are set to zero.

The EMC1402 has two selectable temperature ranges. The default range is from 0°C to +127°C and

the temperature is represented as binary number able to report a temperature from 0°C to +127.875°C

in 0.125°C steps.

The extended range is an extended temperature range from -64°C to +191°C. The data format is a

binary number offset by 64°C. The extended range is used to measure temperature diodes with a large

known offset (such as AMD processor diodes) where the diode temperature plus the offset would be

equivalent to a temperature higher than +127°C.

where:

k = Boltzmann’s constant

T = absolute temperature in Kelvin

[1]

q = electron charge

η = diode ideality factor

Figure 5.4 Block Diagram of Temperature Monitoring Circuit

⎟⎟

⎠

⎞

⎜⎜

⎝

⎛

LOW

HIGH

Anti-

Aliasing

Filter

ΔΣ

ADC

Resistance

Error

Correction

Substrate

PNP

ILOW

IHIGH

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