TEA1081 Philips Semiconductors, TEA1081 Datasheet - Page 4

• Manufacturer Part Number: TEA1081
• Description: Supply circuit with power-down for telephone set peripherals
• Manufacturer: Philips Semiconductors

Philips Semiconductors
FUNCTIONAL DESCRIPTION
The TEA1081 is a supply interface between telephone line
and peripheral devices in the telephone set. The high input
impedance of the circuit allows direct connection to the
telephone line (via a diode bridge). An inductor function is
obtained by amplifier A1, resistor R
external low-pass RC filter.
Under the control of amplifier A2, transistor TR1 supplies
peripheral devices and transistor TR2 minimizes line
signal distortion by momentarily diverting input current to
ground whenever the instantaneous value of the line
voltage drops below the output voltage.
Internal circuits are biased by a temperature and line
voltage compensated reference current source.
The power-down circuit isolates the supply circuit from
external circuitry.
Line terminals: LN and VN (pins 1 and 2)
The input terminals LN and VN can be connected directly
to the line. The minimum DC line voltage required at the
input is expressed by formula (1); see also Table 1.
Table 1 Explanation of formula (1).
The internal current (I
at V
V
Supply terminals: QS and VA (pins 7 and 6)
Peripheral devices are supplied from QS (pin 7). Two
modes of output voltage regulation are available.
O
The TEA1081 operates in this mode when there is no
external resistor (R
September 1994
I
R
V
V
1
LN
UTPUT VOLTAGE FOLLOWS LINE VOLTAGE
SYMBOL
LNmin
LN(P)
S
Supply circuit with power-down for
telephone set peripherals
LN
= 12 V.
= 4 V and reaches a maximum of 1.4 mA at
V
LN
=
input current
internal series resistance
minimum instantaneous line voltage
(1.4 V at I
required peak level of AC line voltage
I
1
V
R
) between QS and VA (see Fig.6).
INT
S
+
O
) at I
V
= 5 mA)
LNmin
DESCRIPTION
O
= 0 mA is typically 0.8 mA
+
V
S
LN P
(see Fig.1) and an
(
SEE FIG
V
.3)
(1)
4
The output voltage follows the line voltage and is
expressed by formula (2); see also Table 2.
Table 2 Explanation of formula (2).
R
The circuit operates in this mode when an external resistor
(R
The output voltage is held constant at V
as soon as the line voltage
V
The control current I6 is typically 20 A.
V
I
R
handbook, halfpage
1
LN
EGULATED OUTPUT VOLTAGE
SYMBOL
LN
S
V
Application without R
(1) I
(2) I
(3) I
) is connected between QS and VA (see Fig.6).
Fig.3 Output voltage as a function of line voltage.
> (2
V O
(V)
1
1
1
10
= 5 mA.
= 20 mA.
= 30 mA; not valid for TEA1081T.
8
6
4
2
0
0
I
6
V
O
line voltage
input current
internal series resistance
R
=
V
2
+ I
V
V
.
LN
1
–
R
I
4
1
S
+ 0.5) (V)
DESCRIPTION
R
(
SEE FIG
S
(2)
+
(1)
6
0.5
(3)
Product specification
.4)
O
V
8
TEA1081
= 2
V
LN
MLC168
(V)
I
6
10
R
V
(V)
(2)