TDE1708DFT(2007) 查看數據表（PDF） - STMicroelectronics
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TDE1708DFT Datasheet PDF : 14 Pages
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TDE1708DFT
Application information
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 1MΩ 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
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