Datasheet

TMP431
TMP432
www.ti.com SBOS441F –SEPTEMBER 2009–REVISED AUGUST 2013
APPLICATION INFORMATION
controlling the emitter current provided acceptable
The TMP431 (two-channel) and TMP432 (three-
temperature measurement results. At 90nm process
channel) are digital temperature sensors that
geometry and below, however, the beta factor
combine a local die temperature measurement
continues to decrease and the premise that it is
channel and a remote junction temperature
independent of collector current becomes less
measurement channel in a single VSSOP-8
certain.
(TMP431) or VSSOP-10 (TMP432) package. They
are Two-Wire- and SMBus interface-compatible and To manage this increasing temperature measurement
are specified over a temperature range of –40°C to error, the TMP431/32 control the collector current
+125°C. The TMP431/32 contain multiple registers instead of the emitter current. The TMP431/32
for holding configuration information, temperature automatically detect and choose the correct range
measurement results, temperature comparator depending on the beta factor of the external
maximum/minimum limits, and status information. transistor. This auto-ranging is performed at the
User-programmed high and low temperature limits beginning of each temperature conversion in order to
stored in the TMP431/32 can be used to trigger an correct for any changes in the beta factor as a result
over/under temperature alarm (ALERT) on local and of temperature variation. The device can operate a
remote temperatures. Additional thermal limits can be PNP transistor with a beta factor as low as 0.1. See
programmed into the TMP431/32 and used to trigger the Beta Compensation Configuration Register
another flag (THERM) that can be used to initiate a section for further information.
system response to rising temperatures.
SERIES RESISTANCE CANCELLATION
For proper remote temperature sensing operation, the
TMP431 requires only a transistor connected
Series resistance in an application circuit that typically
between DXP and DXN; the TMP432 requires
results from printed circuit board (PCB) trace
transistors conncected between DXP1 and DXN1,
resistance and remote line length is automatically
and between DXP2 and DXN2.
cancelled by the TMP431/32, preventing what would
otherwise result in a temperature offset. A total of up
The SCL and SDA interface pins require pull-up
to 1kΩ of series line resistance is cancelled by the
resistors as part of the communication bus, while
TMP431/32 if beta correction is disabled and up to
ALERT and THERM are open-drain outputs that also
300Ω of series line resistance is cancelled if beta
need pull-up resistors. ALERT and THERM may be
correction is enabled, eliminating the need for
shared with other devices if desired for a wired-OR
additional characterization and temperature offset
implementation. A 0.1μF power-supply bypass
correction. See the two Remote Temperature Error vs
capacitor is recommended for good local bypassing.
Series Resistance typical characteristic curves
See Figure 15 for a typical configuration of the
(Figure 7 and Figure 8) for details on the effects of
TMP431; see Figure 16 for a typical configuration of
series resistance on sensed remote temperature
the TMP432.
error.
BETA COMPENSATION
DIFFERENTIAL INPUT CAPACITANCE
Previous generations of remote junction temperature
The TMP431/32 can tolerate differential input
sensors were operated by controlling the emitter
capacitance of up to 2200pF with minimal change in
current of the sensing transistor. However,
temperature error. The effect of capacitance on
examination of the physics of a transistor shows that
sensed remote temperature error is illustrated in
V
BE
is actually a function of the collector current. If
Figure 9 and Figure 10, Remote Temperature Error
beta is independent of the collector current, then V
BE
vs Differential Capacitance. See the Filtering section
may be calculated from the emitter current. In earlier
for suggested component values where filtering
generations of processors that contained PNP
unwanted coupled signals is needed.
transistors connected to these temperature sensors,
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