1°C Triple SMBus Sensor with Resistance Error Correction
Datasheet
4.1
Temperature Monitors
Thermal diode temperature measurements are based on the change in forward bias voltage (ΔVBE) of
a diode when operated at two different currents:
where:
k = Boltzmann’s constant
⎛
⎞
ηkT
q
IHIGH
T = absolute temperature in Kelvin
q = electron charge
⎜
⎜
⎟
⎟
ΔVBE =VBE _ HIGH −VBE _ LOW
=
ln
ILOW
⎝
⎠
η = diode ideality factor
The change in ΔVBE voltage is proportional to absolute temperature T.
VDD
Ilow
Ibias
Ihigh
11-bit Output
Delta Vbe
Sample
&
1-bit
Sigma
Delta
Digital
Averaging
Filter
Hold
Modulator
Internal or
Remote Diode
Bias
Diode
Figure 4.3 Detailed Block Diagram
Figure 4.3 shows a detailed block diagram of the temperature measurement circuit. The EMC1033
incorporates switched capacitor technology that integrates the temperature diode ΔVBE from different
bias currents. The negative terminal, DN, for the temperature diode is internally biased with a forward
diode voltage referenced to ground.
The advantages of this architecture over Nyquist rate FLASH or SAR converters are superb linearity
and inherent noise immunity. The linearity can be directly attributed to the delta-sigma ADC single-bit
comparator while the noise immunity is achieved by the ~20ms integration time which translates to
50Hz input noise bandwidth.
4.2
4.3
Resistance Error Correction
The EMC1033 includes active resistance error correction implemented in the analog front end of the
chip. Without this automatic feature, voltage developed across the parasitic resistance in the remote
diode path causes the temperature to read higher than the true zone temperature. The error introduced
by parasitic resistance is approximately +0.7°C per ohm. Sources of parasitic resistance include bulk
resistance in the remote temperature transistor junctions along with resistance in the printed circuit
board traces and package leads.
Resistance error correction in the EMC1033 eliminates the need to characterize and compensate for
parasitic resistance in the remote diode path.
Programmable Ideality Factor
Temperature sensors like the EMC1033 are typically designed for remote diodes with an ideality factor
of 1.008. When the diode does not have this exact factor, an error is introduced in the temperature
measurement. Programmable offset registers are sometimes used to compensate for this error, but
this correction is only perfect at one temperature since the error introduced by ideality factor mismatch
Revision 1.1 (01-19-07)
SMSC EMC1033
DATA1S0HEET
SMSC [ SMSC CORPORATION ]
