1°C Triple SMBus Temperature Sensor
Datasheet
V
DD
I
high
I
low
I
bias
fs
fs
fs
fs/2048
Internal or
Remote Diode
Bias
Diode
Delta Vbe
Sample
&
Hold
1-bit
Sigma
Delta
Modulator
Digital
Averaging
Filter
11-bit
Accurate
Conversion
Figure 3.2 Block Diagram of Temperature Measurement Circuit
shows a detailed block diagram of the temperature measurement circuit. As shown, the
EMCT03 incorporates switched capacitor technology that samples the external remote temperature
diode voltage at two bias currents and holds the difference voltage. The sample frequency is 100kHz
and the current levels Ihigh and Ilow are 170uA and 10uA respectively. The negative terminal for the
remote temperature diode, DN, is internally biased with a forward diode voltage referenced to ground.
The output of the switched capacitor sample and hold circuit interfaces to a single-bit sigma delta
analog-to-digital converter. This ADC runs at 100kHz sample frequency and its output is digitally filtered
and averaged over 2048 samples effectively generating 11 bit accuracy.
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 sigma delta ADC single-bit
comparator while the noise immunity is achieved by the digital averaging filter. The overall effective
bandwidth of the system is fs/2048 which translates to a 50Hz bandwidth at 100kHz sample rate.
Conversion time equals about 20ms per temperature monitor which equals 60ms total for three
monitors when configured for maximum conversion rate (default).
The 11 bit conversion can be displayed in either legacy format or in extended range format. In Legacy
format, the temperature range covers –64ºC to 127ºC while in extended format, temperature readings
span -64ºC to 191ºC. It should be noted that the latter range is really meant to cover thermal diodes
with a non ideal curvature caused by factor n in equation (1) not being equal to exactly 1.000. In
general, it is not recommended to run silicon based thermal diodes at temperatures above 150ºC.
3.2
System Management Bus Interface Protocol
The EMCT03 communicates with a host controller, such as an SMSC SIO, through the SMBus. The
SMBus is a two wire serial communication protocol between a computer host and its peripheral
devices. Detailed timing diagrams can be found in the electrical characteristics of the SMBus. The
EMCT03 is SMBus 2.0 compatible and supports Write Byte and Read Byte as valid protocols as shown
below:
SMSC EMCT03
DATASHEET
7
Revision 2.3 (04-19-05)
SMSC [ SMSC CORPORATION ]
