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APPLICATION INFORMATION

SERIES RESISTANCE CANCELLATION

0.1mF

10kW

(typ)

10kW

(typ)

10kW

(typ)

TMP400

D+

D-

V+

2

14

12

11

7,8

4

3

R

(2)

S

R

(2)

S

C

(3)

DIFF

C

(3)

DIFF

R

(2)

S

R

(2)

S

GND

SCL

SDA

ALERT

+5V

Two-WireBus/

SMBus Controller

Diode-connectedconfiguration :

(1)

SeriesResistance

Transistor-connectedconfiguration :

(1)

STBY

A

0

A

1

15

10

6

TMP400

SBOS404 – DECEMBER 2007

other

devices

if

desired

for

a

wired-OR

The TMP400 is a dual-channel digital temperature

implementation.

A

0.1

µF power-supply bypass

sensor

that

combines

a

local

die

temperature

capacitor is recommended for good local bypassing.

measurement

channel

and

a

remote

junction

Figure 11 shows a typical configuration for the

temperature measurement channel in a QSSOP-16

TMP400.

package. The TMP400 is Two-Wire and SMBus

interface-compatible,

and

is

specified

over

a

temperature range of –40

°C to +125°C. The TMP400

contains multiple registers for holding configuration

Series resistance in an application circuit that typically

information,

temperature

measurement

results,

results

from

printed

circuit

board

(PCB)

trace

temperature comparator maximum/minimum limits,

resistance and remote line length (see Figure 11) can

and status information.

be automatically programmed to be cancelled by the

TMP400 by setting the RC bit to '1' in the Resolution

User-programmed high and low temperature limits

Register, preventing what would otherwise result in a

stored in the TMP400 can be used to monitor local

temperature offset.

and remote temperatures to trigger an over/under

temperature alarm (ALERT).

A total of up to 3k

Ω of series line resistance is

cancelled by the TMP400 if the RC bit is enabled,

The TMP400 requires only a transistor connected

eliminating the need for additional characterization

between D+ and D– for proper remote temperature

and temperature offset correction. Upon power-up,

sensing operation. The SCL and SDA interface pins

the RC bit is disabled (RC = 0).

require pull-up resistors as part of the communication

bus, while ALERT is an open-drain output that also

See the two Remote Temperature Error vs Series

needs a pull

−up resistor. ALERT may be shared with

Resistance typical characteristics curves (Figure 4

and Figure 5) for details on the effect of series

resistance and power-supply voltage on sensed

remote temperature error.

(1) Diode-connected configuration provides better settling time. Transistor-connected configuration provides better series resistance

cancellation.

Figure 11. Basic Connections

6

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