EMC1402-2-ACZL-TR(2007) Ver la hoja de datos (PDF) - SMSC -> Microchip

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EMC1402-2-ACZL-TR
(Rev.:2007)

1°C Temperature Sensor with Beta Compensation

SMSC -> Microchip 

1°C Temperature Sensor with Beta Compensation

Datasheet

When the THERM pin is asserted, the Therm status bits will likewise be set. Reading these bits will

not clear them until the THERM pin is deasserted. Once the THERM pin is deasserted, the THERM

status bits will be automatically cleared.

5.3

5.3.1

5.3.2

ALERT Output

The ALERT pin is an open drain output and requires a pull-up resistor to VDD and has two modes of

operation: interrupt mode and comparator Mode. The mode of the ALERT output is selected via the

ALERT / COMP bit in the Configuration Register (see Section 6.4).

ALERT Pin Interrupt Mode

When configured to operate in interrupt mode, the ALERT pin asserts low when an out of limit

measurement (> high limit or < low limit) is detected on any diode or when a diode fault is detected.

The ALERT pin will remain asserted as long as an out-of-limit condition remains. Once the out-of-limit

condition has been removed, the ALERT pin will remain asserted until the appropriate status bits are

cleared.

The ALERT pin can be masked by setting the MASK bit. Once the ALERT pin has been masked, it

will be de-asserted and remain de-asserted until the MASK bit is cleared by the user. Any interrupt

conditions that occur while the ALERT pin is masked will update the Status Register normally.

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.

ALERT Pin Comparator Mode

When the ALERT pin is configured to operate in comparator mode it will be asserted if 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 bit will not block the ALERT pin in this mode, however the individual channel masks (see

Section 6.10) will prevent the respective channel from asserting the ALERT pin.

5.4

Beta Compensation

The EMC1402 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.

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.

5.5

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.

Revision 1.16 (03-15-07)

18

DATASHEET

SMSC EMC1402

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