PBL3852 查看數據表（PDF） - Ericsson

零件编号

产品描述 (功能)

比赛名单

PBL3852

Universal Transmission Circuit

Ericsson  

PBL 3852

line resistance RLine and the line feeding

data of the exchange. A decoupling

capacitor is needed between pins +C and

-L. The V+C supply changes its voltage

linearly with the line current. It can be

used to feed an electret microphone.

Caution must be taken though not to drain

too much current out of this output

because it will affect the internal quick

start circuit by locking itself into active

state. (max. permissible current drain

600µA)

Care has to be taken when desiding the

resistance value of R19. All resistances

that are applied from +Line to ground

(-Line) will be in parallel, forming the real

impedance towards the line. This will

sometimes result in, that the ohmic value

of R19 is increased in order to comply to

the impedance specification towards the

line. The speech circuit sinks ≈ 1mA into

the pin 4, which means that the working

voltage for the speech function +V will

decrease with the increasing R19, thus

starving in the end the circuit of its

working voltage. This dependency is often

falsely taken as a sign of that the circuit

does not work down to the low line current

specified, but in fact it is the working

voltage at pin 4 that has became too low.

It is obvious that this problem is also

connected into what kind of DC-

characteristic is set (see fig. 22).

The circuit has further two temperature

and line current compensated DC

supplies DC1 and DC2. DC1 is a high

precision voltage supply for supplying

microphones, opto couplers etc. it is also

suitable as a voltage reference. Typical

voltage 2.1V down to line voltage of 4.1V,

in case the line voltage is lower than 4.1V

calculate; actual line voltage minus 1.9V.

In order to prevent noise entering the

line, a resistor is recommended in series

with this output.

DC2 is a voltage clamped current

source that is suitable to be used in

supplying diallers and micro processors

but also parts of circuitry that need supply

in hook on condition. The typical voltage

is 3.7V down to line voltage of 4.75V If the

line voltage is lower than 4.75V calculate;

actual line voltage minus 1.25V. The

current supply to a memory retention

capacitor is easiest isolated with a diode,

the capacitor preferably a low voltage

drop type, and in hook on condition it has

to have charge path from an uninterrupted

point on the + line. If a diode is not used

for isolation care must be taken that no

current can be taken out of the reservoir

capacitor at or after ”hook-on”. It must be

secured that the receiver can not get any

input signal and that there is a capacitor

in series with the output to isolate a DC

load. It is possible to feed an external

shunt regulator directly from the DC2

output for lower voltage than the clamp

level. The line voltage can for a short

period of time go below the voltage at

this output without affecting the line

characteristics, this because the circuit

tries to keep the current taken from the

line constant at all times. The receiver

has its current supply (pt. a in fig. 22)

from the DC2 supply. A series resistor at

the output will limit the peak current

which is one way to limit the possibility

for an acoustic shock at the earphone.

The handsfree circuits ( PBL 3786,

3786/2 and 3880) speech switching

function can be supplied directly from this

output.

The fourth DC-supply VPh has an

advantage that it does not influence the

circuits DC characteristics even at high

current drain. The supply has a floating

ground reference and is used to supply

the power amplifier of a handsfree

telephone. (PBL 3786, 3786/2 and 3880)

These circuits have a current controlled

charging of the supply capacitor and the

control signal is taken across the

resistorR7.

In case a monitor amplifier is required

where the ground reference is hardly

necessary, it can be supplied from VPh .

IL

RL

R feed

+

VE

VL R19

V+C

PBL 3852

+

+C

V

4

I

Ref

+

+

Clamp

Clamp

-

+

a

8

Lim

9

3

DC2

DC2

+

C9

+

C3

DC1

TI

R3

DC1

+

C2

DCC

5

I/U

+L

1

IT

VT

+

T

-

ƒ

14

2

-L

TO IS

R7

Figure 22. DC-supplies.

+Line

R Ph

IPh

VPh

+

CPh

-Line

15

Share Link: