PBL 386 15/1
Battery Switch
mA
30
To reduce short loop power dissipation, a
second battery voltage, Off-hook, must be
connected to the device via an external
diode at terminal VBAT2. The SLIC auto-
matically switches between the two battery
supply voltages without need for external
control.ThesilentbatteryswitchingtoVBAT
occurs when the line current is below 5.5
mA. This means that the current in the On-
hookbatteryislimitedto6mA. Tocalculate
the switching voltage use this formula (See
formula C in figure 17):
25
20
15
10
5
I
B2
I
B
0
0Ω 1000Ω 2500Ω
5000Ω
7500Ω
10000Ω
∞ Ω
VTR =| VB2 | -4.4 - 50 · ILProg
Figure 12. Chart describing current in Vbat and Vbat2.
If metering is used see section Metering
Applications down below.
mW
V
BAT 2
Connect the terminal VBAT2 to the
second power supply via the diode DB2 in
figure 15. A diode DBB connected between
VB and the VB2 power supply, see figure
15, will make sure that the SLIC continues
to work on the second battery even if the
first battery voltage disappears.
800
700
600
500
400
300
200
100
0
28 V
25 V
22 V
The current commute between the differ-
ent batteries as shown in figure 12, note
that some current is sourced from VB (typ.
0.5 mA, internal bias current) when the line
currentissourcedfromVB2.Thenextchart
(figure 13) is showing what power dissipa-
tion the SLIC is using with different batter-
ies and variation of the line.
0Ω 1000Ω 2500Ω
5000Ω
7500Ω
10000Ω
∞ Ω
Figure 13. Chart describing Power dissipation with different Vbat2.
Metering Applications, TTX
It is very easy to use PBL 386 15/1 in
metering applications; simply connect a
where:
It is possible to mix voice voltage and
meteringvoltageupto2.5Vpeak(1.7Vrms),
between the TIP and RING terminals using AOV. Use following formula to
ZLTTX is the line impedance seen by the 12 calculatetheswitchingvoltageoftheBattery
suitable resistor (RTTX
) in series with a
VTTX is the wanted metering voltage
capacitor (CTTX) between pin RSN and the
meteringsource.CapacitorCTTX decouples
all DC-voltages that may be superimposed
onthemeteringsignal.Themeteringsignal
gain can be calculated from the equation:
or 16 kHz metering signal,
G2-4S is the transmit gain through the SLIC,
i e 0.5.
Switch to get enough signal space.
VTR =| VB2 | -3.4 -Vvoice-VTTX- 50 · ILProg
where:
Vvoice is the voice voltage, normaly 1 Vpeak
VTR
VTTX
G4-2TTX
=
=
VTTX is the the metering voltage in peak.
ZT
ZLTTX
.
RTTX ZT + G2-4S . (ZLTTX + 2RF)
αRSN
13
ERICSSON [ ERICSSON ]
