AP3102/V/L

Document number: DS37419 Rev.2 - 2

8 of 14

www.diodes.com

July 2014

© Diodes Incorporated

AP3102/V/L

A Product Line of

Diodes Incorporated

Operation Description

The AP3102/V/L 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 versatile protection functions for system designer.

Start-up Current and UVLO

The start-up current of AP3102/V/L is optimized to realize ultra low current (5

A 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.

A UVLO comparator is included in AP3102/V/L to detect the voltage on the VCC pin. It ensures AP3102/V/L to draw adequate energy from hold-

up capacitor during power-on. The turn-on threshold is 16V and the turn-off threshold is 10V.

Oscillator

The oscillation frequency is programmed by the value of resistor R8, 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.

The oscillation frequency can be expressed as:

)

(

)

(

8

1720

kHz

k

R

f





The recommended oscillation frequency is 40 to 130kHz from the EMI consideration.

Current Sense Comparator and PWM Latch

AP3102/V/L operates as a current mode controller; the output switch conduction is initiated by every oscillator cycle and 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

S

FB

PK

R

V

I

3

/

)

9

.

0

(





Abnormal operating conditions occur when the power supply output is overloaded or the output voltage sensing is lost. Under these conditions, the

voltage, the constant over load protection can be achieved by compensating the delay time effect from the input line. The maximum peak switch

current is:

S

BOK

MAX

PK

R

V

I

/

)

055

.

0

85

.

0

(

)

(







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. A resistor is usually connected to the current sense pin to avoid the PCB trace interference and it also can

adjust the inductor peak current tinily by the resistance. Of course, adding a RC filter to CS pin is better to attenuate any unexpected noise.

Built-in Slope Compensation

It is well known that a continuous current mode SMPS may become unstable when the duty cycle exceeds 50%. The built-in slope compensation

can improve the stability, so there is no need for design engineer to spend much time on that.

FB Pin and Short Circuit Protection

This pin is normally connected to the opto-coupler and always paralleled with a capacitor for loop compensation. When the voltage at this pin is

greater than 4.2V (such as output short to ground or the opto-coupler is broken) and lasts for about 35ms, the IC will enter the protection mode.

For AP3102, 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

removes. For AP3102V, the IC will be latched unless unplugging the AC socket. Moreover, if the voltage is less than 0.7V, the IC will stop the

drive pulse immediately. Therefore, this feature can be used for short circuit protection, which makes the system immune from catastrophic failure.