|||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
PT0324S-1 12/21/10
5
PT8A2803
500mA Li-ion/Polymer Battery Charger
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
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.
CH
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 200k 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 k.
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 k. The actual charge current is guaranteed to have 10% accuracy of I
CHG
with the charge current set at 150mA.
BAT pin
Always connect the BAT pin to a single-cell Li-ion/Polymer battery in parallel with a 1µF (or larger) X5R ceramic capacitor for
decoupling and guaranteeing system stability. When the
EN
pin is pulled to logic HIGH, the BAT output is disabled. The
PT8A2803 relies on a battery for stability and is not guaranteed to be stable if the battery is not connected.
Dropout Voltage
When the input voltage is low while the battery voltage is high, the charging current may not be maintained according to the
equation I
MIN
(mA) = 4180/R
IMIN
due to a limited internal on-resistance (R
DS(ON)
) of the internal pass element. The worst resistance
of the pass FET is about 1.2 at the maximum operating temperature, thus if tested with 500mA current and 4.2V battery voltage,
constant current could still be maintained when the input voltage is below 4.62V.
Thermal Foldback
The bottom big exposed pad in DFN package is used for thermal foldback. For reducing the chip ambient temperature as much as
possible, it is recommended to connect as much copper as possible to this pad either on the component layer or other layers
through thermal vias. The thermal regulation function starts to reduce the charge current when the internal temperature reaches a
typical value of 115°C.
