DATASHEET

SMT172

last update

maart 20, 2017

reference

V14

page

8

Supply voltage decoupling/cable compensation.

It is common practice for precision analogue ICs to use a decoupling capacitor between Vcc and GND

pins. This capacitor ensures a better overall EMI/EMC performance. When applied, this capacitor should

be a ceramic type and have a value of approximately 100nF. The location should be as close to the sensor

as possible. The SMT172 has a very accurate output, the positive and negative edges of the output signal

are very steep, about 5ns. This means when using longer cables (over 30cm) there can be an effect of the

cable inductance and capacitance which means the pulse is “reflected” and will give a spike on the

sensors power supply line and the output of the sensor. These spikes can damage the electronics behind

line a resistor of (R1) 100/1000Ω.

In case the cable capacitance is big and the edges disturbs the electronics in the device, an alternative

solution is to put a series resistor of 100/500Ω (R2) in the output line of the sensor. It must be realised this

will cause the positive and negative edges to be less steep, so the accuracy of the measured temperature

is influenced. In case the SMT172 is used as a replacement of the SMT160 this accuracy problem will not

be an issue.

will also limit the maximum current in case of faults or wrong connections.

1

2

3

Local electronics

GND

OUT

SMT172

100nF

R1

R2