AN929 Datasheet, PDF (18/22 Pages) Microchip Technology – Temperature Measurement Circuits for Embedded Applications

AN929
Serial I/O sensors can be used to monitor multiple
temperatures on the same PCB and minimize the
number of microcontroller interface pins. Most silicon
sensors available today are designed using the SPI,
V_DD
100 kΩ
1 kΩ 1 kΩ
the two-wire SMBus or I²C protocols. Also, a number of
temperature sensors are available that use a single I/O
pin to transmit information using a pulse-width coding
scheme.
GP2/INT
Data
Clock
PIC16LF872
PICmicro^®
MCU
System
Controller
Data
Clock
V_DD
A_{0 Alert}
A₁
A_{2 TCN75}
Sensor #0
Data
Clock
V_DD
A_{0 Alert}
A₁
A_{2 TCN75}
Sensor #1
Data
Clock
A_{0 Alert}
A₁
A_{2 TCN75}
Sensor #7
TCN75
SD ADC
Diode
V_DD
Temperature
Sensor
Alert
Clock
Generator
Counter /
Accumulator
Control
Logic
Address
Decoder
Serial Bus
Interface
Data Registers
Temperature Data
Calibration Registers
Offset Correction
Temperature Setpoint
Gain Correction
Temperature Hysteresis
Set Point Comparator
Configuration Registers
Control
Manufacture ID
A₀
A₁
A₂
Data
Clock
V_DD
FIGURE 29:
Multi-Zone Temperature Monitoring with the TCN75 Thermal Sensor.
Figure 29 provides a multi-zone temperature monitor
that uses the TCN75 sensor to notify the host controller
when the ambient temperature exceeds a user-
programmed set point. Communication with the TCN75
sensor is accomplished via a two-wire serial bus. The
microcontroller can monitor the temperature of each
sensor by reading the Temperature Data register or the
sensor can function as a stand-alone thermostat. The
temperature threshold trip point is programmed by
writing to the Set Point register. The INT pin is an open-
drain output that can be connected to the microcontrol-
ler’s interrupt pin to monitor up to eight sensors. Three
address pins are used to identify each sensor.
ANALOG OUTPUT
Analog output silicon sensors have an output voltage in
the form of the equation of a straight line. The slope of
the output is equal to a constant temperature
coefficient (mV/°C), while the y-intercept point typically
is the sensor’s output voltage at 0°C. A simplified
schematic of an analog sensor and ADC system is
shown in Figure 30.
DS00929A-page 18
 2004 Microchip Technology Inc.