Technical data

Hardware and Firmware
Designer Reference Manual DRM043/D — Rev 0
10 Hardware and Firmware MOTOROLA
2.2.1 Power supply to the MCU
Please refer to the schematic at 3.5 Schematics
The power input to the charger should be a regulated 5V, 1A supply to
P1.
TL431 is used in this reference design to act as a voltage regulator with
1% accuracy to provide power to the micro-controller.
2.2.2 Charging control
Pin 7 of the MCU is the TCH0 which is configured as a PWM output. The
PWM signal will control the on-off charging power to the battery, and
thus control the charging current and voltage. Q2, D1,L1 and C4 form the
bulk regulator will provide a smoother power source to charge the
battery.
2.2.3 Sensing circuit.
Three ADC channels of the micro-controller are used to check battery's
voltage, current and temperature.
Charging current is sensed at the B- of J1. When battery is under
charging, charging current will flow through the sensing resistor R13 and
R14. A voltage drop will appear on the resistor R13 and R14. It can be
sensed at B-. Since R13//R14 is 0.5 ohms, so when a charge current is
300mA, then the voltage at B- will be 150mV.
The battery voltage is sensed by directly sensing the voltage at B+ point
of J1.
When battery is under charging, it is required to subtract the voltage at
B- in order to obtain the actual battery voltage across its terminals.
The battery's temperature can be sensed by sensing the voltage at
terminal T of J1. The change of voltage is caused by the variation of
resistance value of the NTC.
Frees
cale Semiconductor,
I
Freescale Semiconductor, Inc.
For More Information On This Product,
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