AP3105 datasheet(9/13 Pages) DIODES

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AP3105/V/L/R

Document number: DS36927 Rev. 2 - 2

9 of 13

www.diodes.com

February 2014

AP3105/V/L/R

A Product Line of

Diodes Incorporated

Operation Description (Cont.)

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 and lasts for about 32ms, the IC will enter the protection mode. For AP3105/V/R, 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 1.55V, the IC will stop

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

Normally, output short makes the VFB value to the maximum because the opto-coupler is cut off.

VCC Maintain Mode

During light load or step load, VFB will drop and be lower than 1.55V, thus the PWM drive signal will be stopped, and there is no more new energy

transferred due to no switching. Therefore, the IC supply voltage may reduce to the shutdown threshold voltage and system may enter the

unexpected restart mode. To avoid this, the AP3105/V/L/R hold a so-called VCC maintain mode which can supply energy to VCC.

When VCC decreases to a setting threshold, the VCC maintain comparator will output some drive signal to make the system switch and provide a

proper energy to VCC pin. The VCC maintain function will cooperate the PWM and burst mode loop which can make the output voltage variation be

within the regulation. This mode is very useful for reducing startup resistor loss and achieving a better standby performance with a low value VCC

capacitor. The VCC is not easy to touch the shutdown threshold during the startup process and step load. This will also simplify the system design.

The normal VCC voltage is suggested to be designed a little higher than VCC maintain threshold thus can achieve the best balance between the

standby and step load performance.

System Protection and Pin Fault Protection

The AP3105/V/L/R 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 opto-coupler broken protection. The AP3105/V/L/R also has pin fault connection protection including floating and short connection. The

floating pin protection include the SENSE, FB, etc.. The short pin protection includes the CTRL pin short protection. When these pins are floated

or CTRL pin is shorted to ground, PWM switching will be disabled, thus protecting the power system.

Latch Protection Function

For some applications, the system requires the latch protection function. The CTRL pin has two kinds of modes to trigger the latch protection: high

level trigger and low level trigger. The low threshold is 0.5V and high threshold voltage is 2.5V. Some version will have only one mode. Once the

latch protection is triggered, the IC will disable the output signal, and the bulk capacitor provides the energy to IC through the startup resistor to

ensure the IC disable the output (latch mode). This mode will not be released until the AC input is shut off. So, the de-latch time is mainly

depending on the HV startup bulk capacitor value. Therefore, if the system wants a short de-latch time, it is better for the startup resistor take

power from the point before the rectifier bridge as illustrated in below figure.

VCC

GND

CTRL

AP3105V/L/R

SENSE

AC Mains

(90V to 265V)

CBUS

GATE

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