AP3103 datasheet(10/14 Pages) BCDSEMI

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VERSATILE COST EFFECTIVE GREEN PWM CONTROLLER

AP3103

Preliminary Datasheet

Feb. 2010 Rev. 1. 0

BCD Semiconductor Manufacturing Limited

Operation Description

The AP3103 is specifically designed for off-line AC-

DC power supply used in LCD monitor, notebook

adapter and battery charger applications. It offers a cost

effective solution with a versatile protection function.

Start-up Current and UVLO

The start-up current of AP3103 is optimized to realize

ultra low current (5

µA typical) so that VCC capacitor

can be charged more quickly. The direct benefit of low

start-up current is the availability of using large start-

up resistor, which minimizes the resistor power loss for

high voltage AC input.

An UVLO comparator is included in AP3103 to detect

the voltage on the VCC pin. It ensures that AP3103 can

draw adequate energy from hold-up capacitor during

power on. The turn-on threshold is 15V and the turn-

off threshold is 8.8V.

Oscillator

The oscillation frequency is programmed by the value

of resistor R1, connected from pin RI to ground. The

resistor will make a constant current source to

determine the oscillation frequency by charging and

discharging an internal capacitor. Normally, RI pin

should not be placed where exists too much noise, as

the disturbance may make the IC work abnormally.

The oscillation frequency can be expressed as:

The recommended oscillation frequency is 50 to 100

kHz from the EMI consideration.

Current Sense Comparator and PWM

Latch

The AP3103 operates as a current mode controller; the

output switch conduction is initiated by every

oscillator cycle and is terminated when the peak

inductor current reaches the threshold level established

by the FB pin. The inductor current signal is converted

to a voltage signal by inserting a reference sense

resistor RS. The inductor current under normal

operating conditions is controlled by the voltage at FB

pin, the relation between peak inductor current (IPK)

and VFB is:

Leading-edge Blanking

A narrow spike on the leading edge of the current

waveform can usually be observed when the power

MOSFET is turned on. A 250ns leading-edge blank is

built-in to prevent the false-triggering caused by the

turn-on spike. During this period, the current limit

comparator is disabled and the gate driver can not be

switched off.

FB Pin and Short Circuit Protection

This pin is normally connected to the opt-coupler and

always pa ra llele d wi th a capacitor for loop

compensation. When the voltage at this pin is great

than 4.2V (such as output short to ground or the opt-

coupler is broken) and lasts for about 25ms, the IC will

enter the protection mode. For AP3103, the system will

enter hiccup mode to wait the VCC decreasing to low

UVLO level, then the IC will try to restart until the

failure removed. And when this voltage is less than

1.5V, the IC will stop the drive pulse immediately.

Therefore, this feature can be used for short circuit

protection, which makes the systemimmune from

catastrophic failure. Normally, output short makes the

VFB value to the maximum because the opt-coupler is

cut off.

System Protection and Pin Fault

Protection

The AP3103 provides versatile system and pin fault

protections. The OCP comparator realizes the cycle-

by-cycle current limiting (OCP).In universal input line

voltage, the IC realizes the constant over load

protection (OLP). VCC over voltage protection can be

applied as the primary OVP or opt-coupler broken

protection. The AP3103 also has pin fault connection

protection including floating and short connection. The

floating pin protection include the RI, SENSE, FB, etc;

The short pin protection includes the RI pin short

protection. When these pins are floated or RI pin is

shorted to ground, PWM switching will be disabled,

thus protecting the power system.

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