Motorola Internal Use
9
P7389i – Circuit Description
For DHFA Charger - 2.75V
For Fast Charger – 2.13V
•
Senses battery voltage (
GCAP II
Pin F7
–
BATTERY
)
•
Senses input B+ level
GCAP II
Pin E10
–
B+
)
3)
Charger Power Source: The L7389, 9 used the mid rate charger.
This will not be
available to the P7389I, if used the unit will power down!
When the charger is connected into the accessory plug
J600
,
EXT B+
will be
available at
Pin 14
. This will be sensed at
GCAP II U900
Pin D10
MOBPORTB
.
Once sensed the power will then be passed through the
protection diode CR903
and
made available as
B+.
NB. The charger supports the phone in conjunction with the batteries, therefore the
batteries are charged as
B+
is supplied.
4)
The
GCAP II
is programmed to Boost mode (5.6V) by
PGB0
Pin G7
and
PGM1
Pin
G8
both being tied to Ground. Once
B+
is applied to GCAP II
Pin K5
, all the
appropriate voltages to supply the circuit are provided. These are:
•
V1
– Programmed to 5.0V.
V1
is at 2.775V at immediate power on, but is ‘boosted’
to 5.0V through the switch mode power supply
L901 / CR902
and
C913
. See Fig 6.1
for basic operation.
V1
supplies the DSC bus drivers, negative voltage regulators and
MAGIC DM.
V1
is created from GCAP II
Pin A6
and can be measured on
C906
.
The basic circuit operation for the Boost circuit is as follows the
LX
signal (GCAP II
Pin B10
) allows a path for
B+
to charge the capacitor, when the switch is on, the
capacitor then discharges through the inductor (switch off), setting up an electric
field. The field then collapses setting up a back EMF to charge the capacitor, and so
on and so on. The back EMF created by the inductor is greater than
B+
with the +ve
half of the cycle passing through the diode to charge a capacitor from where the
V_BOOST
voltage is taken. The frequency of the switching signal
LX
decides the
duty cycle of the output wave and therefore the resultant voltage.
V_BOOST
is fed
back into the GCAP.
•
V2
– Programmed to 2.775V, available whenever the radio is on and supplies most of
the logic side of the board.
V2
is supplied out of GCAP II
Pin J2
and can be
measured on either
C939
or
C941
.
Logic memory circuitry differs from that of the standard Leap by using 2 x 4Mbit
SRAM instead of 1 x 2Mbit SRAM band also using Whitecap SPS ROM 6. This
change is incorporated to allow the extra memory capacity for GPRS operation.
LX
Output
B+ FREAK
Fig 6.1