Multiple Channel 1°C Temperature Sensor with Beta Compensation
Datasheet
6.3
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 7.4).
6.3.1
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_ALL bit. Once the ALERT pin has been masked,
it will be de-asserted and remain de-asserted until the MASK_ALL bit is cleared by the user. Any
interrupt conditions that occur while the ALERT pin is masked will update the Status Register normally.
There are also individual channel masks (see Section 7.10).
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 7.10) will prevent the respective channel from asserting the ALERT pin.
6.4
Temperature Measurement
The EMC1412 can monitor the temperature of one externally connected diode. The 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 EMC1412 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.
Revision 1.41 (02-23-12)
SMSC EMC1412
DATA2S0HEET
SMSC [ SMSC CORPORATION ]
