EMC1413 datasheet(21/52 Pages) SMSC

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Multiple Channel 1°C Temperature Sensors with Beta Compensation

Datasheet

SMSC EMC1413 / EMC1414

Revision 1.41 (02-23-12)

DATASHEET

The ALERT pin is used as an interrupt signal or as an SMBus Alert signal that allows an SMBus slave

to communicate an error condition to the master. One or more ALERT outputs can be hard-wired

together.

6.3.2

ALERT Pin Comparator Mode

When the ALERT pin is configured to operate in comparator mode, it will be asserted if any of the

measured temperatures exceeds the respective high limit. The ALERT pin will remain asserted until

all temperatures drop below the corresponding high limit minus the Therm Hysteresis value.

When the ALERT pin is asserted in comparator mode, the corresponding high limit status bits will be

set. Reading these bits will not clear them until the ALERT pin is deasserted. Once the ALERT pin is

deasserted, the status bits will be automatically cleared.

The MASK_ALL bit will not block the ALERT pin in this mode; however, the individual channel masks

(see Section 7.11) will prevent the respective channel from asserting the ALERT pin.

6.4

Temperature Measurement

The EMC1413 / EMC1414 can monitor the temperature of up to two / three externally connected

diodes. Each external diode channel is configured with Resistance Error Correction and Beta

Compensation based on user settings and system requirements.

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). If the measured temperature meets or exceeds the

Therm Limit, the THERM pin is asserted unconditionally, providing two tiers of temperature detection.

6.4.1

Beta Compensation

The EMC1413 / EMC1414 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 EMC1414, the External Diode 2 and External Diode 3 channels do not support Beta

Compensation.

6.4.2

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.

Contributors to series resistance are PCB trace resistance, on die (i.e. on the processor) metal

resistance, bulk resistance in the base and emitter of the temperature transistor. Typically, the error

caused by series resistance is +0.7°C per ohm. The EMC1413 / EMC1414 automatically corrects up

to 100 ohms of series resistance.

6.4.3

Programmable External Diode Ideality Factor

The EMC1413 / EMC1414 is designed for external diodes with an ideality factor of 1.008. Not all

external diodes, processor or discrete, will have this exact value. This variation of the ideality factor

introduces error in the temperature measurement which must be corrected for. This correction is

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