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2003 Microchip Technology Inc. DS00871A-page 1
M
AN871
INTRODUCTION
The TC72 and TC77 are CMOS silicon temperature
sensors that provide an accurate digital temperature
measurement to solve thermal measurement problems.
Data is converted from an internal diode temperature-
sensing element to a digital format that can be directly
interfaced to a microcontroller, as shown in Figure 1.
The TC72 and TC77 sensors offer many system-level
advantages, including the integration of the sensor and
signal conditioning circuitry in a small Integrated Circuit
(IC) package.
The main distinguishing feature of the TC72 is its One-
shot Operating mode, which performs a single temper-
ature measurement and then goes into power-saving
Shutdown mode. The One-shot mode makes the TC72
sensor a good choice for power-critical, portable appli-
cations. The main feature of the TC77 sensor is its
excellent temperature accuracy specification of 1°C
from +25°C to +65°C (max.), making this device an
excellent choice for precision temperature-sensing
applications.
The circuitry inside the TC72 and TC77 will be ana-
lyzed to illustrate the principles that these sensors use
to accurately measure temperature. In addition, appli-
cation guidelines will be provided that can maximize
the accuracy of the temperature measurement.
SILICON IC SENSOR
FUNDAMENTALS
Temperature Measurement Diode
IC sensors measure temperature by monitoring the
voltage across a diode. The TC72 and TC77 use a
bipolar temperature-sensing diode that is built from the
substrate of a CMOS IC process. The bipolar diode is
created from a PNP transistor that is formed by
combining the appropriate P and N junctions, as shown
in Figure 2. This method of creating the bipolar
substrate diode is also used by the band gap voltage
reference circuit that is used in almost every analog
and digital IC.
FIGURE 1: Typical Applications of the
TC72
and
TC77
Temperature Sensors.
Author: Jim Lepkowski,
Microchip Technology Inc.
AN0
SCK
SDI
CE
SCK
SDO
TC72
0.1 µF
V
DD
GND
V
DD
PICmicro
®
MCU
SDOSDI
AN0
SCK
SDI
CS
SCK
SI/O
TC77
0.1 µF
V
DD
V
SS
V
DD
PICmicro
®
MCU
SDO
Solving Thermal Measurement Problems Using The TC72
And TC77 Digital Silicon Temperature Sensors
