EMC1402_12 Datasheet, PDF (20/40 Pages) SMSC Corporation – 1°C Temperature Sensor with Beta Compensation

5.10
1°C Temperature Sensor with Beta Compensation
Datasheet
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:
Δ V _BE
= ^{η kT}
q
ln
⎜⎜⎝⎛
I _HIGH
I _LOW
⎟⎟⎠⎞
where:
k = Boltzmann’s constant
T = absolute temperature in Kelvin
[1]
q = electron charge
η = diode ideality factor
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.
I_LOW
I_HIGH
Substrate
PNP
Resistance
Error
Correction
DP
Anti-
Aliasing
Filter
ΔΣ
ADC
DN
Figure 5.4 Block Diagram of Temperature Monitoring Circuit
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.
Table 5.2 shows the default and extended range formats.
Revision 2.0 (08-10-12)
20
DATASHEET
SMSC EMC1402