AL1697 datasheet(6/13 Pages) DIODES

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AL1697

Document number: DS38223 Rev. 3 - 2

6 of 13

www.diodes.com

January 2016

AL1697

Functional Description and Application Information

Convertor Operation

The AL1697 is a single stage, single winding, high efficiency, and high power factor LED driver converter for dimmable LED lamp applications. It is

available in two internal High-Voltage MOSFET options for

4Ω and 1.8Ω with Super-Junction which reduce the overall LED driver solution size of

the LED lamp. Two different MOSFET options are targeted at optimizing the solutions of different LED chain lengths and powers.

High power factor (PF) is achieved using constant on-time mode; coupled with simple closed loop of constant current control the AL1697 achieves

good line and load regulation. The AL1697 adopts source-driver technique to decrease the system operating current. It uses a novel method to

detect the tOFF time which results in the removal for the need of an auxiliary winding for (VCC supply and) detecting the tOFF time, which enables the

AL1697 to have an extremely low bill material (BOM) solution. The AL1697 operates at boundary conduction mode (BCM) which can ease EMI

design.

GND

Input

FR1

DB1

COMP

VCC

LEDS

Figure 1. Typical Application Circuit

Start-up and Supply Voltage

Before start-up, the VCC capacitor C4 is charged by the startup resistors (R2, R3) from the high voltage mains. When the start-up voltage is

reached, the AL1697 starts switching. During normal operation, the VCC supply is provided by start-up resisters (R2, R3) and the output voltage

(VOUT) rectified by one diode (D2). In this way the system can provide VCC supply at low dimming angle.

The AL1697 has an internal VCC clamp voltage (typical 15.5V), which is limited by one internal active Zener diode.

When VCC voltage drops to below the VOPR(Min), switching is stop. So the device can operate normally when the voltage on VCC pin is between

VOPR(MIN) and VCC clamp voltage.

Protections

Under Voltage Lockout (UVLO)

When the voltage on the VCC pin drops to below VOPR(MIN), the IC stops switching. The IC can restart when the voltage on VCC exceeds the

startup voltage (VTH(ST)).

Leading-Edge Blanking (LEB)

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

short current spike can occur because of the capacitive discharge of the voltage over the drain and source. It is disregarded during the LEB time

(tON_MIN).

Cycle-by-cycle Over Current Protection (OCP)

The AL1697 has a built-in peak current detector. It triggers when the voltage on CS pin reaches the peak level VCS_CLAMP. The R5 is connected to

the CS pin to sense the current of the inductor. The maximum peak current (IPEAK(MAX))of the inductor can be calculated as below:

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