TCA505BG Datasheet, PDF (4/18 Pages) Siemens Semiconductor Group – IC for Inductive Proximity Switches with Short-Circuit Protection

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).
By means of an external distance resistor on the oscillator (pin RDi) it is possible to set the
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
RHy (see application circuit 1).
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
connected to VREF, Q2 and Q4 can be used between 0 V and VREF. The maximum base voltage
of the output transistors can be set on pin B. If B is connected to VREF, any constant current up
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.
By means of a capacitor on CD it is possible to set the response delay and the turn-OFF time
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
buildup of the oscillator. Finally CD produces a turn-OFF delay of the output stages to prevent
the turn-ON delay from running its full length at brief voltage dips on VS.
A switching regulator is incorporated for the voltage supply of the circuit when it is used as a
two-wire AC proximity switch, and this is activated when pin VT is connected to VS. The circuit
has a stabilized voltage of approx. 2.9 V that is brought out on pin VREF.
Supply-voltage range: The operating range in normal operation is between 4 and 40 V. If pin
VREF is connected to VS, the circuit is operating between 3.1 and 4.5 V. In this case, however,
VREF is no longer internally stabilized, i.e. the analog IC functions depend on the operating
voltage.
Semiconductor Group
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