Dual RPM-Based PWM Fan Controller with Hardware Thermal Shutdown
Datasheet
Appendix A Thermistors
The EMC2104 can monitor thermistor inputs on the TRIP_SET / VIN4 as well as supporting a
thermistor option on the all of the external diode pins pairs (DP1 / VREF_T1 and DN1 / VIN1,etc.).
The Thermistors can be connected as shown in Figure A.1.
Figure A.1 is representative of one of the thermistor channels and will apply to DP1 / VREF_T1 and
DN1 / VIN1, DP2 / VREF_T2 and DN2 / VIN2.
The top side resistor is internally integrated in the case of the TRIP_SET / VIN4 channel and the VREF
voltage will not be brought out externally. The Thermistor should be connected in the same way as
RSET.
EMC2104/5/6
DP3 / DN4 / VREF_T3
Reference
Buffer
Voltage
1.2K
1%
DN3 / DP4 / VIN3
ADC
10K 1%
Thermistor
0.1uF
Figure A.1 “Low Side” Thermistor Connection
The relationship between voltage and temperature is roughly linear. the measured voltage by the
EMC2104 will be inversely proportional to temperature .
Linearization methods can only accurately capture the temperature over a limited window of
temperatures.
For a 10k Ohm type 3370 Thermistor and a 1.2k ohm ±1% setting resistor, the output response
corresponding to a thermistor is tabulated in Table A.1.
If the INV_VINx bit is set then the results of the circuit (configured as shown in Figure A.1) is shown
in Table A.2.
The EMC2104 does not perform any numerical calculations on the thermistor value if a thermistor is
monitored on TRIP_SET / VIN4 pin. If the External Diode 1, External Diode 2, or External Diode 3
channels are configured to measure a thermistor, it must be configured as shown in Figure A.1.
When measuring a thermistor input with Fan Control Look Up Table, care must be taken that the
temperature thresholds are entered as a unsigned voltage number that corresponds to the desired
thermal threshold. Also note that the LUT assumes that the VIN1 and TRIP_SET / VIN4 voltage inputs
are directly proportional to temperature.
Revision 1.74 (05-08-08)
SMSC EMC2104
DATA8S6HEET
SMSC [ SMSC CORPORATION ]
