DATASHEET

SMT172

last update

maart 20, 2017

reference

V14

page

3

Absolute Maximum Rating

Power supply voltage

-0.5V to 7V

Output pin load

50mA

Operating temperature range

-55°C

Storage temperature range

-60°C to 150°C

ESD protection (HBM)

2000V

Junction temperature

200°C

Soldering temperature (SOIC, SOT)

260°C (10s)

Smartec BV.

Output Signal

According to tradition, the Smartec temperature sensors have a duty cycle (PWM) output that can be directly

interfaced with a microcontroller without the use of extra components. The output is a square wave with a

well-defined temperature-dependent duty cycle. In general, the duty cycle of the output signal is defined by a

linear equation:

= .

+ .

×

where

DC = Valid Duty Cycle

T = Temperature in °C

A simple calculation shows that, i.e. at 0°C, DC=0.32 (32%); at 130°C, DC=0.931 (93.1%).

The temperature is derived from the measured duty cycle by:

=

.

.

= 212.77 ×

− 68.085

The frequency of the sensor output varies with the temperature and the supply voltage, but it does not

contain temperature information. Only the duty cycle contains temperature information in accordance to the

formula given above.

A higher accuracy can be achieved when a second order formula is used, an accuracy of ±0.1°C can be

achieved in the range of -20°C to 60°C.

Valid Duty Cycle

A valid duty cycle in equation (1) is defined as the average of individual duty cycles from 8 consequent

output periods. This is due to the internal working principle of the SMT172 sensor. In order to eliminate the

error caused by component mismatching, DEM (Dynamic Element Matching) has been applied in SMT172. A

complete DEM cycle consists 8 periods. There might be large variation between each individual period, and

this variation changes from sensor to sensor, but the averaged value of 8 consequent periods (valid duty

cycle) is very stable and precise.