EMC1188 Datasheet, PDF (21/48 Pages) Microchip Technology – Notebook Computers

Quad Channel 1°C Temperature Sensor with Hardware Thermal Shutdown and 1.8V SMBus Communications
Datasheet
+3.3V
VDD 1
DP1 2
DN1 3
DP2/DN3 4
DN2/DP3 ⁵
EMC1188
10 _SMCLK
9 SMDATA
8 _ALERT
7 SYS_SHDN
6 ^GND
4.7K -
33K
+3.3V
4.7K -
33K
+2.5 - 5V
22K
Shared Alert
+2.5 - 5V
22K
Shared SYS_SHDN
Figure 5.3 Isolating ALERT and SYS_SHDN Pin
5.7
5.7.1
5.7.2
Temperature Measurement
The EMC1188 can monitor the temperature of up to three externally connected diode.
The device contains programmable High, Low, and Therm limits for all measured temperature
channels. If the measured temperature goes below the Low limit or above the High limit, the ALERT
pin can be asserted (based on user settings).
Beta Compensation
The EMC1188 is configured to monitor the temperature of basic diodes (e.g., 2N3904) or CPU thermal
diodes. It automatically detects the type of external diode (CPU diode or diode connected transistor)
and determines the optimal setting to reduce temperature errors introduced by beta variation.
Compensating for this error is also known as implementing the transistor or BJT model for temperature
measurement.
For discrete transistors configured with the collector and base shorted together, the beta is generally
sufficiently high such that the percent change in beta variation is very small. For example, a 10%
variation in beta for two forced emitter currents with a transistor whose ideal beta is 50 would contribute
approximately 0.25°C error at 100°C. However for substrate transistors where the base-emitter junction
is used for temperature measurement and the collector is tied to the substrate, the proportional beta
variation will cause large error. For example, a 10% variation in beta for two forced emitter currents
with a transistor whose ideal beta is 0.5 would contribute approximately 8.25°C error at 100°C.
For the EMC1188 the External Diode 2 and External Diode 3 channels do not support Beta
Compensation.
Resistance Error Correction (REC)
Parasitic resistance in series with the external diodes will limit the accuracy obtainable from
temperature measurement devices. The voltage developed across this resistance by the switching
diode currents cause the temperature measurement to read higher than the true temperature.
SMSC EMC1188
21
DATASHEET
Revision 1.0 (07-11-13)