TMP435ADGST datasheet(9/35 Pages) TI1

9 / 35 page

TMP435

www.ti.com

SBOS495A – MARCH 2010 – REVISED APRIL 2010

APPLICATION INFORMATION

correct for any changes in the beta factor as a result

The TMP435 (two-channel) is a digital temperature

of temperature variation. The device can operate a

sensor

that

combines

local

die

temperature

PNP transistor with a beta factor as low as 0.1. See

measurement

channel

and

remote

junction

the

Beta

Compensation

Configuration

temperature

measurement

channel

single

section for further information.

package. This device is two-wire- and SMBus

interface-compatible,

and

specified

over

Series Resistance Cancellation

temperature range of –40°C to +125°C. The TMP435

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 is automatically

and status information. User-programmed high and

cancelled by the TMP435, preventing what would

low temperature limits stored in the TMP435 can be

otherwise result in a temperature offset. A total of up

used to trigger an over/under temperature alarm

to 1k

Ω of series line resistance is cancelled by the

(ALERT)

local

and

remote

temperatures.

TMP435 if beta correction is disabled and up to 300

Ω

Additional thermal limits can be programmed into the

of series line resistance is canceled if beta correction

TMP435 and used to trigger another flag (THERM)

enabled,

eliminating

the

need

for

additional

that can be used to initiate a system response to

characterization and temperature offset correction.

rising temperatures.

See the two Remote Temperature Error vs Series

Resistance typical characteristic curves (Figure 7 and

For proper remote temperature sensing operation, the

Figure 8) for details on the effect of series resistance

TMP435

requires

only

transistor

connected

on sensed remote temperature error.

between DXP and DXN.

The SCL and SDA interface pins require pull-up

Differential Input Capacitance

resistors as part of the communication bus, while

The

TMP435

can

tolerate

differential

input

ALERT and THERM are open-drain outputs that also

capacitance of up to 2200pF with minimal change in

need pull-up resistors. ALERT and THERM may be

temperature error. The effect of capacitance on

shared with other devices if desired for a wired-OR

sensed remote temperature error is illustrated in

implementation.

0.1mF

power-supply

bypass

Figure 9 and Figure 10, Remote Temperature Error

capacitor is recommended for good local bypassing.

vs Differential Capacitance. See the Filtering section

See Figure 13 for a typical configuration.

for suggested component values where filtering

unwanted coupled signals is needed.

Beta Compensation

Previous generations of remote junction temperature

Temperature Measurement Data

sensors were operated by controlling the emitter

Temperature measurement data are taken over a

current

the

sensing

transistor.

However,

default range of 0°C to +127°C for both local and

examination of the physics of a transistor shows that

remote

locations.

However,

measurements

from

VBE is actually a function of the collector current. If

–55°C to +150°C can be made both locally and

beta is independent of the collector current, then VBE

remotely

reconfiguring

the

TMP435

for

the

may be calculated from the emitter current. In earlier

extended temperature range, as described in this

generations

processors

that

contained

PNP

section. Temperature data resulting from conversions

transistors connected to these temperature sensors,

within

the

default

measurement

range

are

controlling the emitter current provided acceptable

represented in binary form, as shown in Table 1,

temperature measurement results. At 90nm process

Standard Binary column. Note that any temperature

geometry and below, the beta factor continues to

below 0°C results in a data value of zero (00h).

decrease and the premise that it is independent of

Likewise, temperatures above +127°C result in a

collector current becomes less certain.

value of 127 (7Fh). The device can be set to measure

To manage this increasing temperature measurement

over an extended temperature range by changing bit

error, the TMP435 controls the collector current

2 (RANGE) of Configuration Register 1 from low to

instead

the

emitter

current.

The

TMP435

high. The change in measurement range and data

automatically detects and chooses the correct range

format from standard binary to extended binary

depending

the

beta

factor

the

external

occurs at the next temperature conversion.

transistor. This auto-ranging is performed at the

beginning of each temperature conversion in order to

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