EMC2104 datasheet(86/101 Pages) SMSC

86 / 101 page

Dual RPM-Based PWM Fan Controller with Hardware Thermal Shutdown

Datasheet

Revision 1.74 (05-08-08)

SMSC EMC2104

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.

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.

Figure A.1 “Low Side” Thermistor Connection

10K 1%

Thermistor

DP3 / DN4 / VREF_T3

DN3 / DP4 / VIN3

1.2K

0.1uF

EMC2104/5/6

ADC

Buffer

Reference

Voltage

EMC2104 Fiches technique(PDF) 86 Page - SMSC Corporation