emc1413 Standard Microsystems Corp., emc1413 Datasheet - Page 20

• Manufacturer Part Number: emc1413
• Description: 1?c Temperature Sensor With Beta Compensation And Selectable Address
• Manufacturer: Standard Microsystems Corp.

Revision 1.37 (12-23-09)
5.3.1
5.3.2
5.4
5.5
5.6
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 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 6.11, "Channel Mask
pin.
The EMC1413 and EMC1414 are 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 the External Diode 1 channel only. 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.
The External Diode 2 and External Diode 3 channels do not support Beta Compensation.
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 and EMC1414 automatically correct up
to 100 ohms of series resistance.
The EMC1413 and 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
Beta Compensation
Resistance Error Correction (REC)
Programmable External Diode Ideality Factor
Register") will prevent the respective channel from asserting the ALERT
DATASHEET
1°C Temperature Sensor with Beta Compensation and Selectable Address
20
SMSC EMC1413 / EMC1414
Datasheet