TMP442 datasheet(20/29 Pages) TI1

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HIGH-SPEED MODE

UNDERVOLTAGE LOCKOUT

TIMEOUT FUNCTION

GENERAL CALL RESET

SHUTDOWN MODE (SD)

FILTERING

SENSOR FAULT

TMP441

TMP442

SBOS425A – DECEMBER 2008 – REVISED MARCH 2009 .............................................................................................................................................. www.ti.com

When

not

using

the

remote

sensor

with

the

TMP441/42, the DXP and DXN inputs must be

In order for the Two-Wire bus to operate at

connected together to prevent meaningless fault

frequencies above 400kHz, the master device must

warnings.

issue a High-Speed mode (Hs-mode) master code

(0000 1xxx) as the first byte after a START condition

to switch the bus to high-speed operation. The

TMP441/42 acknowledge this byte, but switch the

The

TMP441/42

sense

when

the

power-supply

input filters on SDA and SCL and the output filter on

voltage has reached a minimum voltage level for the

SDA to operate in Hs-mode, allowing transfers at up

ADC to function. The detection circuitry consists of a

to 3.4MHz. After the Hs-mode master code has been

voltage comparator that enables the ADC after the

issued, the master transmits a Two-Wire slave

power supply (V+) exceeds 2.45V (typical). The

address to initiate a data transfer operation. The bus

comparator output is continuously checked during a

continues to operate in Hs-mode until a STOP

conversion. The TMP441/42 do not perform a

condition occurs on the bus. Upon receiving the

temperature conversion if the power supply is not

STOP condition, the TMP441/42 switch the input and

valid. The PVLD bit (bit 1, see Table 3) of the

output filters back to fast mode operation.

Local/Remote Temperature Register is set to '1' and

the temperature result may be incorrect.

The TMP441/42 reset the serial interface if either

SCL or SDA are held low for 32ms (typical) between

The TMP441/42 support reset via the Two-Wire

a START and STOP condition. If the TMP441/42 are

General

Call

address

00h

(0000

0000b).

The

holding the bus low, they release the bus and waits

TMP441/42 acknowledge the General Call address

for a START condition. To avoid activating the

and respond to the second byte. If the second byte is

timeout function, it is necessary to maintain a

06h

(0000

0110b),

the

TMP441/42

execute

communication speed of at least 1kHz for the SCL

software reset. This software reset restores the

operating frequency.

power-on reset state to all TMP441/42 registers, and

aborts any conversion in progress. The TMP441/42

take no action in response to other values in the

second byte.

The TMP441/42 Shutdown Mode allows maximum

power to be saved by shutting down all device

circuitry other than the serial interface, reducing

current consumption to typically less than 3

µA; see

Remote junction temperature sensors are usually

Figure 6, Shutdown Quiescent Current vs Supply

implemented in a noisy

environment.

Noise

Voltage. Shutdown Mode is enabled when the SD bit

frequently generated by fast digital signals and if not

of the Configuration Register is high; the device shuts

filtered properly will induce errors that can corrupt

down once the current conversion is completed.

temperature measurements. The TMP441/42 have a

When SD is low, the device maintains a continuous

built-in 65kHz filter on the inputs of DXP and DXN to

conversion state.

minimize the effects of noise. However, a differential

low-pass filter can help attenuate unwanted coupled

signals. If filtering is needed, suggested component

values are 100pF and 50

Ω on each input; exact

The TMP441/42 can sense a fault at the DXP input

values

are

application-specific.

also

resulting from incorrect diode connection and can

recommended that the capacitor value remains

sense an open circuit. Short-circuit conditions return a

between 0pF to 330pF with a series resistance less

value of –64°C. The detection circuitry consists of a

than 1k

Ω.

voltage comparator that trips when the voltage at

DXP exceeds (V+) – 0.6V (typical). The comparator

output is continuously checked during a conversion. If

a fault is detected, the OPEN bit (bit 0) in the

temperature result register is set to '1' and the rest of

the register bits should be ignored.

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