Semiconductor Group

4

TCA 505 BG

Functional Description

This circuit is used to design inductive proximity switches. The resonant circuit of the LC

oscillator is implemented with an open half-pot ferrite and a capacitor in parallel (pin LC). If a

metallic target is moved closer to the open side of the half-pot ferrite, energy is drawn from the

resonant circuit and the amplitude of the oscillation is reduced accordingly. This change in

amplitude is transmitted to a threshold switch by means of a demodulator and triggers the

outputs (see operation schematic).

switching distance within wide limits, the optimal distances being 0.1 to 0.6 of the diameter of

the half-pot ferrite, although both of these parameters can be exceeded. The circuit also

enables the setting of a path hysteresis by switching of the external distance resistor via pin

There are two antiphase output stages (Q1 / Q2 and Q3 / Q4) for max. 50 mA. The output

transistors are driven in a floating state thus providing the user with optimal flexibility for

evaluation of the output signals. It is therefore possible to use the output transistors either as

emitter follower, open-collector, as a current source or in push-pull operation. When pin B is

to 50 mA can be set on the outputs by means of resistors on Q2 or Q4 (see application

circuits 2 and 3).

Q1 through Q4 and also additional external output transistors can be protected against

destruction by short-circuit or overload. This is the purpose of pin SC which turns off the output

transistors periodically in the presence of overload.

of short-circuit protection. The same capacitor also defines the turn-ON delay of the output

stages when the supply voltage is applied, whereby the output stages are inhibited during

A switching regulator is incorporated for the voltage supply of the circuit when it is used as a

Supply-voltage range: The operating range in normal operation is between 4 and 40 V. If pin

voltage.