PT8A2803 Datasheet, PDF(7/8 Page) Pericom Semiconductor Corporation

◁

PT8A2803

500mA Li-ion/Polymer Battery Charger

|||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||

Application Information

Input Capacitor Selection

The input capacitor is employed to decouple the power supply from load transients and suppress noise from power lines. Typically,

a 1ÂµF X5R ceramic capacitor is recommended to be placed very close between the VIN pin and GND pin to stabilize the operation

during the start up, especially when the input supply is passing the POR threshold and the VIN-BAT comparator offset voltage.

Once passing through the POR threshold, there is a voltage hysteresis to provide sufficient guard band from noise or load transient

to trigger the system to reset.

Output Capacitor Selection

The criterion for selecting the output capacitor is to maintain the stability of the charger as well as to bypass any transient load

current. Typically, a minimum capacitance of 1ÂµF X5R ceramic capacitor is recommended and sufficient for stabilizing the system.

For systems that may happen to occasionally see high load transients, the output capacitor may be increased to further bypass any

ripples so caused.

Charge Current Limit

During the constant-current (CC) charging mode, the charging current is primarily determined by ICHG as calculated in previous

formula. However, the actual charge current is the CC mode could also be limited by other factors as described by below Figure 5.

When the input (VIN) and output (VBAT) voltage are too close to each other, the on-resistance of the internal pass element may

limit the amount of current that passes through it. For example, the solid curve describes a typical case in which the battery voltage

is 4.0V and the charge current (ICHG) is set at 350mA. When the input voltage is sufficiently higher than the battery voltage but has

not increased the die temperature over the thermal limit yet, the charging current is accurately regulated at 350mA.

Figure 5: PT8A2803 Charge Current Limits In CC Mode

When the input voltage is reduced (or the battery voltage is increases towards the input voltage), the charge current is limited by

the on-resistance of the pass element. Therefore, it is recommended to employ sufficiently high input voltage for applications that

require constant charging current over the entire charging period. But for applications that needs to minimize the heat dissipation,

a current-limiting adapter maybe applied to maintain constant charging current at whole charging phase.

In addition, if the input voltage increases, the charge current may also be reduced due to the thermal foldback function. The high

voltage drop across the pass element increases the power dissipation therein and thus causing the die temperature to increase

significantly.

Layout Guidance

The PT8A2803 employs thermally-enhanced DFN package, which have an exposed thermal pad at its bottom side. It is

recommended to connect as much copper as possible between the exposed pad and PCB to make it effective in dissipating the heat

away from the die. For applications requiring high charging current, the thermal impedance should be further reduced by

employing more layers of copper to connect with the exposed pad through thermal via.

Input Power Sources

PT8A2803 works with different types of AC/DC adapter or USB port (any type) with no special requirements. For PT8A2803, it

works with input voltage ranges from 4.3V to 5.5V for normal operation but the maximum input voltage is 7V.

12-03-0002

PT0324-1

03/06/12

▷