Datasheet

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SBOS383C − DECEMBER 2006 − REVISED MAY 2008
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21
SMBUS ALERT FUNCTION
The TMP411 supports the SMBus Alert function. When pin
6 is configured as an alert output, the ALERT
pin of the
TMP411 may be connected as an SMBus Alert signal.
When a master detects an alert condition on the ALERT
line, the master sends an SMBus Alert command
(00011001) on the bus. If the ALERT
pin of the TMP411 is
active, the devices will acknowledge the SMBus Alert
command and respond by returning its slave address on
the SDA line. The eighth bit (LSB) of the slave address
byte indicates whether the temperature exceeding one of
the temperature high limit settings or falling below one of
the temperature low limit settings caused the alert
condition. This bit will be high if the temperature is greater
than or equal to one of the temperature high limit settings;
this bit will be low if the temperature is less than one of the
temperature low limit settings. See Figure 17 for details of
this sequence.
If multiple devices on the bus respond to the SMBus Alert
command, arbitration during the slave address portion of
the SMBus Alert command determines which device will
clear its alert status. If the TMP411 wins the arbitration, its
ALERT
pin becomes inactive at the completion of the
SMBus Alert command. If the TMP411 loses the
arbitration, the ALERT
pin remains active.
SHUTDOWN MODE (SD)
The TMP411 Shutdown Mode allows the user to save
maximum power by shutting down all device circuitry other
than the serial interface, reducing current consumption to
typically less than 3µA; see typical characteristic curve
Shutdown Quiescent Current vs Supply Voltage.
Shutdown Mode is enabled when the SD bit of the
Configuration Register is high; the device shuts down
once the current conversion is completed. When SD is low,
the device maintains a continuous conversion state.
SENSOR FAULT
The TMP411 will sense a fault at the D+ input resulting
from incorrect diode connection or an open circuit. The
detection circuitry consists of a voltage comparator that
trips when the voltage at D+ exceeds (V+) − 0.6V (typical).
The comparator output is continuously checked during a
conversion. If a fault is detected, the last valid measured
temperature is used for the temperature measurement
result, the OPEN bit (Status Register, bit 2) is set high, and,
if the alert function is enabled, ALERT
asserts low.
When not using the remote sensor with the TMP411, the
D+ and D− inputs must be connected together to prevent
meaningless fault warnings.
UNDER-VOLTAGE LOCKOUT
The TMP411 senses when the power-supply voltage has
reached a minimum voltage level for the ADC converter to
function. The detection circuitry consists of a voltage
comparator that enables the ADC converter after the
power supply (V+) exceeds 2.45V (typical). The
comparator output is continuously checked during a
conversion. The TMP411 will not perform a temperature
conversion if the power supply is not valid. The last valid
measured temperature is used for the temperature
measurement result.
GENERAL CALL RESET
The TMP411 supports reset via the Two-Wire General Call
address 00h (0000 0000b). The TMP411 acknowledges
the General Call address and responds to the second byte.
If the second byte is 06h (0000 0110b), the TMP411
executes a software reset. This software reset restores the
power-on reset state to all TMP411 registers, aborts any
conversion in progress, and clears the ALERT
and
THERM
pins. The TMP411 takes no action in response to
other values in the second byte.
IDENTIFICATION REGISTERS
The TMP411 allows for the Two-Wire bus controller to
query the device for manufacturer and device IDs. This
feature allows for software identification of the device at
the particular Two-Wire bus address. The manufacturer ID
is obtained by reading from pointer address FEh. The
TMP411 manufacturer code is 55h. The device ID
depends on the specific model; see the Register Map
(Table 3). These registers are read-only.
FILTERING
Remote junction temperature sensors are usually
implemented in a noisy environment. Noise is most often
created by fast digital signals, and it can corrupt
measurements. The TMP411 has a built-in 65kHz filter on
the inputs of D+ and D− to minimize the effects of noise.
However, a bypass capacitor placed differentially across
the inputs of the remote temperature sensor is
recommended to make the application more robust
against unwanted coupled signals. The value of the
capacitor should be between 100pF and 1nF. Some
applications attain better overall accuracy with additional
series resistance; however, this increased accuracy is
setup-specific. When series resistance is added, the value
should not be greater than 3kΩ.
If filtering is needed, the suggested component values are
100pF and 50Ω on each input. Exact values are
application-specific.