TMP411CD datasheet(21/32 Pages) TI

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TMP411

SBOS383C − DECEMBER 2006 − REVISED MAY 2008

www.ti.com

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 3

µA; see typical characteristic curve

Shutdown

Quiescent

Current

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

the

remote

temperature

sensor

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 3k

Ω.

If filtering is needed, the suggested component values are

100pF and 50

Ω on each input. Exact values are

application-specific.

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