TDE1708DFT

Application information

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3.1

Adjustable input hysteresis circuit

The TDE1708DFT is a device realized in bipolar technology and therefore it has the usual

problems of temperature compensation that such technology involves; despite all it maintains

an input dynamics within 1V over industrial temperatures range.

In all input voltage range it will guarantee a high impedance of 1M

Ω determining an input

current about 2uA.

Exploiting this input high impedance is possible connects a sensor directly on it and bypass the

obstacle of active signal conditioning circuit using a voltage firm point as ground of sensor, the

delay capacitor, connected on the pin 3, as low pass filter and capacitor on Vreg pin to minimize

the noise on it and protect for errors the low-voltage internal circuits, according AN495.

In Figure 5. the input external network is optimized for accepting both a sensor with ground

connected to the body and a sensor with independent ground.

In order to ground the body of the sensor , J1 has to be shorted , while J2 opened and connect

the sensor on M3; in case of independent ground J1 must be opened, J2 shorted and the

sensor connected on M4.

DL1 indicate commutation status of the device output and C3 realize a simple output filtering in

case is used an inductive load. With C2 about 10nF we obtain a good filtering and immunity

from input voltage noise. C4 is 4,7nF according AN495.

R2 is an optional resistor plugged only when the sensor needs to adapt its impedance with the

input impedance of device. .

Figure 5.

Application circuit for adjustable input hysteresis

TDE1708DFT