AL1698 datasheet(8/15 Pages) DIODES

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AL1698

Document number: DS42216 Rev. 1 - 2

8 of 15

www.diodes.com

September 2019

AL1698

Functional Description and Application Information (continued)

Cycle-by-Cycle Over Current Protection (OCP)

The AL1698 has a built-in peak current detector. It is triggered 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:





CS CLAMP

PEAK MAX



……………………(1)

The detection circuit is activated after the LEB time. When the detection circuit senses the CS voltage 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 AL1698 has output open voltage protection when the LED is open, which can prevent the output voltage from increasing to a very high value.

This feature can help the system designer to select a smaller volume capacitor. The output voltage is set by the external resistor R3 shown in

Figure 1.

When LED is open, the tOFF_OVP time can be calculated as:

OFF OVP

OVP







…………… (2)

Where,

VOVP is the output open voltage.

VCS is the voltage on the CS pin when OVP happens.

The output voltage is set by R3, and R3 is calculated as:

)

(

OVP

REF

ROVP





…………… (3)

Where, VROVP_REF is the internal ROVP pin 0.5V’s reference, CREF is the internal 8.07pF capacitor.

Output-Short Protection (OSP)

When LED is shorted, the device cannot detect the tOFF time, and the device controls the system operation at 4kHz low frequency.

Thermal Foldback Protection (TFP)

AL1698 has a Thermal Foldback Protection (TFP) function and adopts self-adaptive control method, which can prevent the system breaking down

caused by high temperature. The overheating temperature is set at +150°C typical. When the junction temperature of the IC is higher than +150°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 system heat quality. This enhances the safety of the system at high

temperature.

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