TCN75A_1 Datasheet, PDF (13/40 Pages) Microchip Technology – 2-Wire Serial Temperature Sensor

5.0 FUNCTIONAL DESCRIPTION
The TCN75A temperature sensor consists of a band-
gap type temperature sensor, a  Analog-to-Digital
Converter (ADC), user-programmable registers and a
2-wire I²C protocol-compatible serial interface.
Resolution
One-Shot
Shutdown
Fault Queue
Alert Polarity
Alert Comp/Int
Configuration
Register
Temperature
Register
T_HYST
Register
T_SET
Register
0.5°C
0.25°C
0.125°C
0.0625°C
 ADC
Band-Gap
Temperature
Sensor
Register
Pointer
I²C™
Interface
FIGURE 5-1:
Functional Block Diagram.
TCN75A
5.1 Temperature Sensor
The TCN75A uses the difference in the base-emitter
voltage of a transistor while its collector current is
changed from IC₁ to IC₂. With this method, the V_BE
depends only on the ratio of the two currents and the
ambient temperature, as shown in Equation 5-1.
EQUATION 5-1:
Where:
V_BE
=


k_--q--T_{-}
 lnIC₁  IC₂
T = temperature in kelvin
V_BE = change in diode base-emitter
voltage
k = Boltzmann’s constant
q = electron charge
IC₁ and IC₂ = currents with n:1 ratio
5.2  Analog-to-Digital Converter
A Sigma-Delta ADC is used to convert V_BE to a digital
word that corresponds to the transistor temperature.
The converter has an adjustable resolution from 0.5°C
(at 30 ms conversion time) to 0.0625°C (at 240 ms
conversion time). Thus, it allows the user to make
trade-offs between resolution and conversion time.
Refer to Section 5.3.2 “Sensor Configuration
Register (CONFIG)” and Section 5.3.4.7 “ ADC
Resolution” for details.
 2010 Microchip Technology Inc.
DS21935D-page 13