AL1697

Document number: DS38223 Rev. 6 - 2

7 of 13

www.diodes.com

October 2017

© Diodes Incorporated

AL1697





_

5

CS CLAMP

PEAK MAX

V

I

R



The detection circuit is activated after the LEB time. When the detection circuit sense the CS voltage is higher than 1V, the IC will turn off the

switching to limit the output current. It automatically provides protection for the maximum LED current during operation. A propagation delay exists

between over current detection and actual source-switch off, so the actual peak current is a little higher than the OCP level set by the R5.

Over-Voltage Protection and Output-Open Protection (OVP)

The output voltage is sensed by the FB pin, which provides an over-voltage protection (OVP) function. When the output is open or large transient

the over voltage condition still exists, the system will work in hiccup mode.

Output-Short Protection (OSP)

Thermal Foldback Protection (TFP)

AL1697 has a thermal foldback function and adopts self-adaptive control method, which can prevent the system breaking down caused by high

temperature. The overheating temperature is set at +145°C typical, when the junction temperature of the IC is higher than +145°C typical, the

device will linearly decrease the internal reference voltage to decrease the output current. As a result of this feature, the device can control the

system

’s output power at high ambient temperature, to control the quantity of heat of the system. This enhances the safety of the system at high

temperature.

The thermal foldback waveform is shown below:

100%

50%

Junction Temperature/

°C

Output Current

OTP

Figure 2. Thermal Foldback Waveform

Over-Temperature Protection (OTP)

The AL1697 has OTP protection function. When the junction temperature reach to +160°C typical, the IC will trigger an over-temperature

protection condition which causes the device to shut down and latched. Once OTP has triggered, the system will resume after the system

’s AC

source supply has been reset and power up.

Design Parameters

Setting the Current Sense Resistor R5

The AL1697 adopts boundary conduction mode, the output current is calculated as below,

_

0

11

sin( )

2

OFF

O MEAN

PEAK

ON

OFF

DELAY

t

I

I

d

t

t

t







 











Where,