Datasheet
2010 Microchip Technology Inc. DS21935D-page 13
TCN75A
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 I
2
C protocol-compatible serial interface.
FIGURE 5-1: Functional Block Diagram.
5.1 Temperature Sensor
The TCN75A uses the difference in the base-emitter
voltage of a transistor while its collector current is
changed from IC
1
to IC
2
. 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:
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.
Resolution
0.5°C
0.25°C
0.125°C
0.0625°C
Temperature
T
HYST
T
SET
Register
Register
Register
Register
Pointer
I
2
C™
Interface
Configuration
Register
ADC
Band-Gap
Temperature
Sensor
One-Shot
Shutdown
Fault Queue
Alert Polarity
Alert Comp/Int
V
BE
kT
q
----- -
ln I C
1
IC
2
=
Where:
T = temperature in kelvin
V
BE
= change in diode base-emitter
voltage
k = Boltzmann’s constant
q = electron charge
IC
1
and IC
2
= currents with n:1 ratio