MC33215 Motorola, MC33215 Datasheet - Page 9

• Manufacturer Part Number: MC33215
• Description: Telephone Line Interface and Speakerphone Circuit
• Manufacturer: Motorola

from Pin REG by the internal circuit (the 10 A term in the
formulas). This built–in feature drops the line voltage and
therefore enables parallel operation.
protect the device. A zener of 11 V at VLN is therefore the
maximum advised.
V
interface is powered via V
power peripherals like a dialer or microcontroller. The voltage
at V
line voltage setting and the current consumption at V
internally (I
biased at 1.8 V higher than SLP. This translates to a
maximum allowable voltage drop across Z
V
maximum allowable current consumption by the peripherals
of 2.0 mA.
VMC Supply
powering the handset microphone. Due to this stabilized
supply, microphones with a low supply rejection can be used
which reduces system costs. In order to support the parallel
operation of the telephone set, the voltage at VMC will be
maintained even at very low line currents down to 4.0 mA.
and above, the supply VMC is able to deliver a guaranteed
minimum of 1.0 mA. However, for lower line currents, the
supply capability of VMC will decrease.
MOTOROLA ANALOG IC DEVICE DATA
DD
zener
The voltage over the line driver has to be limited to 12 V to
The internal circuitry for the line driver and handset
For correct operation, it must be ensured that V
At VMC, a stabilized voltage of 1.75 V is available for
Under normal supply conditions of line currents of 20 mA
DD
Supply
1.8
1.7
1.6
1.5
1.4
1.3
1.2
1.1
1.0
Figure 5. VMC Under Different Microphone Loads
– 1.8 V. In the typical application, this results in a
0
is not internally regulated and is a direct result of the
V
VDD
DD
0.2
) and externally (I
+
VLN – I
0.4
I
line
= 4.0 mA
I
2.7 k VMC–VHF
line
0.6
DD
= 4.0 mA
VDD
. This pin may also be used to
I
VMC
0.8
PER
)
(mA)
I
). It follows that:
PER
1.0
I
line
x R set
= 20 mA
1.2
1.4
VDD
DD
MC33215
DD
1.6
of
is
VMC, a 2.7 k resistor between VMC and VHF can be applied.
In Figure 5, the VMC voltage under different microphone
currents, is shown.
VHF Supply
duplex controller part of the MC33215, and which is also
meant to power the base microphone or other peripherals.
The base microphone however, can also be connected to
VMC, which is preferred in case of microphones with a poor
supply rejection. Another possibility is to create an additional
filter at VHF, like is shown in the typical application. The
supply capability of VHF is guaranteed as 2.0 mA for line
currents of 20 mA and greater.
available to power a loudspeaker and thus having a
speakerphone working, the current internally supplied to VHF
is cut around 10 mA of line current to save current for the
handset operated part. A small hysteresis is built in to avoid
system oscillations.
drop rapidly due to the internal consumption of 1.4 mA and
the consumption of the peripherals. When VHF drops below
2.0 V, the device internally switches to the handset mode,
neglecting the state of the speakerphone select Pin SPS.
mains supplied, speakerphone operation becomes possible
under all line current conditions. In order to avoid switch–over
to handset operation below the 10 mA, VHF has to be
supplied by this additional power source and preferably kept
above 2.4 V.
V
powering the loudspeaker amplifier and peripheral circuitry.
This supply pin should be looked at as a current source since
the voltage on V
instantaneous line voltage and the current to and consumed
from V
at V
V
current to V
source saturates and the surplus of current is conducted to
the power ground PGD to avoid distortion in the line driver. In
fact, when no current is drawn from V
will increase until the current splitter is in balance. In Figure 6
this behavior is depicted.
CC
CC
If, during parallel operation, a high current is required from
VHF is a stabilized supply which powers the internal
Since in parallel operation not enough line current is
When the current to VHF is cut, the voltage at VHF will
In case an application contains a battery pack or if it is
At V
The maximum portion of the line current which is available
This formula is valid when the voltage drop from VLN to
CC
I
Supply
VCC
is sufficient for the current splitter to conduct all this
CC
CC
is given by the following relation:
.
+
the major part of the line current is available for
CC
10
11
. When the drop is not sufficient, the current
CC
x I
is not stabilized and depends on the
line
– I
VDD
CC
– I
, the voltage at V
VMC
– I
VHF
9
CC