PT8A2803 Datasheet, PDF (3/8 Pages) Pericom Semiconductor Corporation – 500mA Li-ion/Polymer Battery Charger

PT8A2803
500mA Li-ion/Polymer Battery Charger
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Functional Description
The PT8A2803 charges a single-cell Li-ion/Polymer battery with a programmable constant current (CC) or a constant voltage (CV)
algorithm. The fast charge current (ICHG) can be programmed by setting an external resistor RIREF (see Figure 3/4) while
constant voltage is factory-trimmed at 4.2V (4.1V or 4.36V) options area available upon request). If the battery voltage was deeply
discharged to lower than 2.55V, PT8A2803 firstly pre-charges the battery with 20% of the programmed fast charge current.
Normally, the battery voltage rises gradually during CC charge phase. When the battery voltage reaches almost 4.2V, the charger
enters the constant-voltage (CV) charging mode and begins to regulate the battery voltage at 4.2V while diminishing the charging
current gradually. When charging current is reduced to an amount smaller than the programmed End-Of-Charge (EOC) current
level, the charger gives out a “full-charge” indication through the CHG pin, but the charger still continues to regulate the battery
voltage at 4.2V with safe & small current. Figure 2 shows the typical charge profile with the EOC/reset event.
PT8A2803 employs current recharge algorithm. The end-of charge (EOC) current level can be easily programmed with an external
resistor RIMIN (see Figure 3/4). The CHG signal turns to LOW when pre-charge starts and rises to HIGH when EOC is reached.
After reaching EOC, the charge current has to rise to typically 76% ICHG before the_CHG signal will turn on again, as shown in
Figure 2. The current surge after EOC can be caused by a load connected to the battery.
When the die temperature reaches 115°C (typically) during charging, a thermal regulation function is employed to reduce the
charge current accordingly to maintain the temperature from increasing furthermore. This is an important function to achieve safe
operation especially when the printed circuit board (PCB) is not effective in leaking out heat generated by the linear charger.
PPR Indication
The PPR pin is implemented as an open-drain output to
provide a power-good indication of the input power source
such as an AC adapter. When the input voltage is higher than
the POR (Power-On Reset) threshold, the PPR pin turns on the
internal open-drain MOSFET to indicate a logic LOW signal.
The PPR indication is designed to be independent on the chip
enable ( EN -pin) input. When the internal open-drain FET is
turned off, the PPR pin should leak less than 1µA current.
When turned on, the PPR pin should be able to sink at least
10mA current under all operating conditions. The PPR pin can
be used to drive an LED (see Figure 3) or worked as logic
interface to a microprocessor (see Figure 4).
Power-Good Range
The input voltage is considered as power good when it meets
the following three conditions:
1. VIN > VPOR
2. VIN - VBAT > VOS
Where the VOS is the offset voltage to determine if the battery
voltage is even higher than the input voltage. All VPOR and
VOS are realized with sufficient hysteresis, as given in the
Electrical Specification table. All charging activities are
disabled when the input voltage falls out of the power-good
range.
Input and Output Comparator
Obviously, when the input source voltage is lower than the
battery voltage, no charging activity could be started and the
charger will disable the internal pass element to prevent
battery leakage. Charge begins when the input voltage is
higher than the battery voltage by a defined offset voltage
(VOS). This scheme also ensures that the charger is
completely turned off when the input power is removed from
the charger.
CHG Indication
The CHG pin is implemented as an open-drain output to give a
logic LOW when a charge cycle begins and turn HIGH when
an end-of-charge (EOC) condition is reached. This pin is
designed with a sinking ability of more than 10mA so as to
drive an LED. When the charger is disabled through EN -pin,
the CHG outputs a high impedance. The CHG pin can also be
used to interface with a microprocessor.
EN Input
The chip is enabled by a logic LOW signal applied to the EN
pin. This pin is realized with a 200kΩ internal pull-down
resistor such that even the EN pin is left floating, the input is
equivalent to logic LOW and the chip is enabled by default.
Similarly, the chip is disabled when the EN pin receives a
logic HIGH signal. The threshold for HIGH is given in the ES
(Electrical Specifications).
IMIN Indication
The IMIN pin can be used to program the End-of-Charge
(EOC) current by connecting a resistor between this pin and
the GND pin. The programming is defined by the following
equation:
IMIN (mA) = 4180/ R_IMIN
Where R_IMIN is usually in kΩ.
IREF Pin
The IREF pin is for fast charge-current programming. By
connecting a resistor between this pin and the GND pin, the
fast charge current limit is determined by the following
equation:
I_CHG (mA) = 4400/R_IREF
Where R_IREF is in kΩ. The actual charge current is guaranteed
to have 10% accuracy of I_CHG with the charge current set at
150mA.
12-03-0002
PT0324-1
03/06/12
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