Motorola Timeport P8190, Service Manual

Page: 93 / 149

Motorola Confidential Proprietary
Theory of Operation Service Manual
81
Audio/Thermistor
The cellular transceiver has the capability
of supporting two batteries, a main battery
and an auxiliary battery. Since a charger cir-
cuit is designed in this unit, there needs to
be a form of reading the thermistor values of
each battery separately. The thermistor
readings are used to determine the tempera-
ture of the battery cell which is being
charged.
In order for the call processor(U1000) to read
the thermistor values of the batteries, a volt-
age needs to be placed across the thermistor.
As the temperature increases the thermistor
will decrease in resistance, causing the sup-
ply level at the thermistor to decrease. The
thermistor line is pulled high by the
THERM_BIAS line.
The transceiver supports three audio output
ports; ear speaker (EAR-), headset speaker
(HDST_SPKR), and external audio port
(AUDIO_OUT). The audio path routing is
controlled by the GCAP2. The call
processor(U1000) programs the GCAP2 to
route the audio to its proper path. When the
transceiver determines that audio needs to
be routed externally, the other two audio
ports are disabled by the GCAP2(U1500).
The audio comes from the EXT_OUT line and
passes through an audio filter before being
sent to the external connector. Because the
AUDIO_OUT line has two multiplexed func-
tions, the audio filter also acts as an isolator
to the ON/OFF function which in the same
line.
When the ear speaker is used, the EAR- and
EAR+ lines are used . The audio signals be-
tween EAR+ and EAR- is 180° out of phase.
This allows proper operation of the ear
speaker.
When a headset is attached to the trans-
ceiver, a headset detect interrupt will have
the audio only go to the headset speaker
(HDST_SPKR). Since the same EAR- line is
used for the headset and the ear speaker, the
ear speaker is disabled by inverting the EAR-
signal 180°. This will present two signals to
the ear speaker that have no phase shift,
thus, not allowing the ear speaker from func-
tioning.
Charger/Batt Select
The internal charger will be activated only
when there is an external power source, a
Motorola battery is attached, the
MAN_TEST line is loaded down, and
BATT_FDBK is enabled. As S
passes thru R1566, U1500(GCAP) reads the
charge current for proper control of the
charger. CHRGC controls the rate of charge
to the batteries by varying the gate biasing
of Q1561.
The output of Q1561 is split into two differ-
ent sections. The one section is the
BATT_FDBAK line. BATT_FDBK_EN
switches Q642 on or off to disable or enable
BATT_FDBAK. When BATT_FDBK is not
available, the external supply will lower it’s
supply to a normal operating voltage and the
internal charger will be turned. The second
section is the line to charge the batteries. The
radio is capable of charging two batteries
(Main and Auxiliary). The phone is designed
to always charge the main battery first. Once
the main battery is fully charged, it will be-
gin charging the auxiliary battery.
Charger/Batt Select