U4078B Datasheet, PDF (2/5 Pages) TEMIC Semiconductors – Tone Ringer Interface with DC/DC Converter

U4078B
TELEFUNKEN Semiconductors
Pin Description
Pin Symbol
Function
1, 8 aȀ, bȀ AC ringing signal input
2
V_B Output to charging capacitor
(for supply)
3
TH Comparator threshold adjustment
input
4
MS Mode selection: inductive or
opto-coupler mode
5
ST Switching transistor connection
6
OSC RC circuit for internal oscillator
input
7
GND Ground
a’ 1
8 b’
VB ₂
TH 3
U4078B
7 GND
6 OSC
MS 4
5 ST
94 7902 e
Functional Description
The ringing ac signal, supplied by the exchange via lines
a, b, is identified by a comparator circuit. An integrated
oscillator, generates a 38 kHz clock signal, f_clock, via a
coupled 2:1 divider. With the help of the external RC
circuit, oscillation frequency is set at Pin 6. A
PNP-transistor connected at Pin 5 enables the power
transmission (transfer) in inductive or opto-coupler mode,
which is selected at Pin 4. For inductive mode, Pin 4 is
open, whereas for opto-coupler mode, Pin 4 is connected
to GND (Pin 7).
Pin 1,8: Power Supply – aȀ, bȀ
Pins 1 and 8 connect the circuit with the ac ringing signal
supplied by the exchange via lines a and b.
A 1µF decoupling capacitor of 1 µF value together with a
series resistance (1.5 kΩ) protect the circuit from overload
across Pins 1 and 8. The circuit features the following
overload protection across the aȀ, bȀ terminals:
1) It can withstand a voltage of 110 V @ 50 Hz for
maximum time of 15 seconds.
2) Testing of the circuit according to figure 2 does not
destroy the circuit under following conditions:
Charging voltage of surge capacitance: V_CS = 2 kV
Pulse shape: 10/700 µs
Pulse sequence: 30 s
No. of surges: 10
Polarity change after 5 surges
Pin 2: Charging Capacitor
(power supply filtering)
After the rectification of the ringing ac signal across the
bridge circuit, the smoothing of the power supply is
provided by the external capacitance at Pin 2 ( 22 nF ).
* Pin 3: Comparator Threshold TH
* * Comparator threshold as regards the ringing voltage
is set at ca. 12.5 V. Switching threshold can be increased or
decreased by connecting a resistance at Pin 3 w.r.t. GND.
* Pin 4: Mode Selection MS
The ringing ac signal transfer (transmission) without
potential loss occurs either via an inductive or opto-coupler
mode. Pin 4 is set to a high state by an internal power source
of 4 µA (approximately). This switches the output (Pin 5)
to an operating state for the inductive mode. In case of
opto-coupler mode, Pin 4 is connected to the ground
(Pin 7).
Pin 5: Switching Transistor Connection
An external PNP transistor, whose emitter is at V_S (Pin 2)
potential, serves to control the inductive or opto-coupler
mode by connecting the base of the transistor with Pin 5.
In case of inductive mode, the signal, f_clock is interrupted
for the duration of t_pulse = 32/f_clock, with every transition
(rise or fall) of the ringing ac signal, f_ring. During the
interruption, the setting at Pin 5 is such that the coil is
critically damped (attenuated), whereas a current of 10 µA
flows when the transistor at Pin 5 is switched on during the
following t_pulse up to the next edge of the pulse.
In case of opto-coupler mode, the external transistor is
switched on for a period of t_pulse = 32/f_clock with every flank
of the pulse of f_ring.
Pin 5 is at high resistance upto the next edge (flank) of the
transition pulse of the ringing ac signal.
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