tea1085t NXP Semiconductors, tea1085t Datasheet - Page 9

• Manufacturer Part Number: tea1085t
• Description: Listening-in Circuit For Line-powered Telephone Sets
• Manufacturer: NXP Semiconductors

Philips Semiconductors
Dynamic limiter (DLC) pin 23
To prevent distortion of the signal at the loudspeaker
outputs the gain of the amplifier is reduced rapidly when:
The time in which the gain reduction is effected is the
'attack time'; this is very short in the first and third instance
and relatively long in the second instance. The circuit will
remain in the gain-reduced condition until the peaks of the
output signal remain below the threshold level. The gain
will then return to a nominal level after a time determined
by the capacitor connected to DLC (release time).
March 1992
handbook, full pagewidth
handbook, full pagewidth
the peaks of the signal at the loudspeaker outputs
exceed an internally determined threshold (voltage
limiter)
the DC current into SUP is insufficient (current limiter)
the voltage at V
determined threshold, typically 2.9 V (V
Listening-in circuit for line-powered
telephone sets
MUTE
QLS1
LSI1
BB
decreases below an internally
standby
Fig.7 Mute switch alternatives with the TEA1085.
(a) Break contact.
Fig.6 Mute toggle function of the TEA1085.
MUTE
BB
limiter)
listening-in
9
MUTE input (MUTE) pin 20; TEA1085A
This MUTE is provided with a logic input to operate with a
microcontroller for instance.
The loudspeaker amplifier is disabled when the MUTE
input is LOW (connected to V
level at the MUTE input enables the amplifier in the
listening-in mode.
MUTE input (MUTE) pin 20; TEA1085
The MUTE function is provided with a toggle input and is
designed to switch between the standby condition and the
listening-in condition on the rising edge of the input MUTE
signal (see Fig.6).
In the basic application the MUTE input must be LOW
(connected to V
operate the MUTE toggle (see Fig.7). Debouncing can be
realized by means of a small capacitor connected between
MUTE and V
An internal start circuit ensures that the circuit always
starts up in the standby condition.
10 k
(b) Make contact.
SS
V BB
MUTE
.
SS
). A simple push-button can be used to
TEA1085; TEA1085A
standby
MLA055
SS
or open input). A HIGH
Preliminary specification
MGR036