Motorola Internal Use
9
A008 / A6188+ – Circuit Description
controlled through
Battery FET Q942
by
GCAP II
Output
Pin F10
and is output as
B+
2)
Once
B+
is available the unit carries out the following checks:
•
The battery temperature is monitored to establish whether rapid charge is required,
(
J610
BATT_THERM_AD
to
GCAP II
Pin B3
)
-40 deg C – 2.75V
25 deg C – 1.39V
40 deg C – 0.96V
•
Charger sensed (
J600
Pin 5
MANTEST_AD
to
GCAP II
Pin A1
) This is achieved
using different sense resistors within the accessory.
For DHFA Charger - 2.75V
For Fast Charger – 2.13V
•
Senses battery voltage (
GCAP II
Pin F7
–
BATT+
)
•
Senses input B+ level
GCAP II
Pin E10
–
B+
)
If
EXT B+
is available the current will be passed through protection diode CR940
and output as
B+
to provide power to the PCB.
3)
The GCAP II is programmed to Boost mode (5.6V) by
PGM0
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 / CR901
and
C934
. See
Fig 6.1
for basic operation.
•
V1
supplies the DSC bus drivers, negative voltage regulators and MAGIC.
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.
On initial power up the
LX
signal is not always immediately correct in frequency,
therefore the duty cycle of the
B+
signal is incorrect which can lead to the switch
mode power supply creating huge current problems. To prevent this
Q9808
is placed
with
Q902
as a protection circuit.
LX
Output
B+
Fig 6.1
