AL1696 datasheet(8/14 Pages) DIODES

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AL1696

Document number: DS38304 Rev. 1 - 2

8 of 14

www.diodes.com

October 2015

AL1696

Functional Description and Application Information

Convertor Operation

The AL1696 is a single stage, single winding inductor, high efficiency, and high power factor LED driver solution for mains input phase-cutting

dimmable application. It is available for three internal MOSFET options (300V/3A, 500V/2A and 600V/2A) which helps to reduce the overall LED

driver solution

’s size and optimize bom cost. The three different MOSFET options can cover most of 3~12W dimmable applications.

The AL1696 internal MOSFET

’s on time is limited by tON_MAX which is set through RT pin and internal 0.4V reference. The MOSFET will be turned

off either its on time triggers tON_MAX or input voltage on CS pin triggers internal 0.4V reference voltage. So if the tON_MAX is set to a very small

value, the system will operate in constant on-time (tON_MAX) mode during the whole rectified mains cycle. It will result in a good power factor, but

the line regulation will be worse. Normally, a recommended tON_MAX should make the system operate in constant on-time (tON_MAX) mode at valley

of input voltage and peak current mode at the crest. A trade off between PF and line regulation need to be done when setting tON_MAX.

The AL1696 adopts source-driver technology to decrease the system operating current. Besides, it uses a novel tOFF time detection method

without auxiliary winding. The AL1696 operates in boundary conduction mode (BCM) which can ease EMI design. All of them help AL1696 to have

an extremely low bill of material (BOM).

Input

FR1

DB1

GND

VCC

LEDS

Figure 1. Typical Buck-Boost Application Circuit

Start-up and Supply Voltage

During start-up, the VCC capacitor C4 is charged through startup resistors (R2, R3) from the rectified mains input until the start-up voltage is

reached, the AL1696 starts switching. In normal operation, the VCC supply is provided from two paths: one is from start-up resisters (R2, R3) and

the other is from output voltage (VOUT) through one diode (D2). In this way the system can provide sufficient VCC supply at low dimming angle.

The AL1696 has internal VCC clamp, the typical voltage is 16V. VCC voltage needs to be between VOPR(min) and VCC_CLAMP during normal

operation.

When VCC voltage drops below the under voltage lockout (UVLO), IC will stop switching. The IC will restart once the voltage on VCC pin exceeds

the startup voltage (VTH(ST)) again.

Protections

Under Voltage Lockout (UVLO)

When the voltage on the VCC pin drops below VOPR(Min), the IC will stop switching. The IC will restart until the VCC voltage exceeds the startup

voltage (VTH (ST)) again.

Leading-Edge Blanking (LEB)

To prevent false detection of the peak current through MOSFET, a blanking time following switch-on is designed. When the internal switch turns

on, a short current spike may appear because of the discharge of the parasitic capacitor over MOSFET

’s drain and source. It will be ignored

during the LEB time (tON_MIN).

Cycle-by-cycle Over Current Protection (OCP)

The AL1696 has a built-in peak current detector. The R5 connected to the CS pin is used to sense the current through MOSFET and will be one of

the inputs. The detection circuit is activated after the LEB time. When the voltage on CS pin reaches VREF, the IC will turn off the switch to limit the

output current.

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