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Axelite Confidential Materials, do not copy or distribute without written consent.

Rev.1.4 Sep.27, 2019

AX2020

Reducing output ripple

Peak to peak ripple current in the LED(s) can be reduced, if required, by shunting a

capacitor CLED across the LED(s) as shown below:

D

VIN

CSN

SW

GND

VIN

DIM

L

47uH

0.4

AX2020

CLED

1uF

CIN

4.7uF~100uF

A value of 1uF will reduce the supply ripple current by a factor three (approx.).

Proportionally lower ripple can be achieved with higher capacitor values. Note that the

capacitor will not affect operating frequency or efficiency, but it will increase start-up delay

and reduce the frequency of dimming, by reducing the rate of rise of LED voltage.

By adding this capacitor the current waveform through the LED(s) changes from a

triangular ramp to a more sinusoidal version without altering the mean current value.

Operation at low supply voltage

The internal regulator disables the drive to the switch until the supply has risen above

the startup threshold (VUVLO). Above this threshold, the device will start to for this reason, the

temperature coefficients of the operating. However, with the supply voltage below the

specified minimum value, the switch duty cycle will be high and the device power dissipation

will be at a maximum. Care should be taken to avoid operating the device under such

conditions in the application, in order to minimize the risk of exceeding the maximum allowed

die temperature. (See next section on thermal considerations). The drive to the switch is

turned off when the supply voltage falls below the under-voltage threshold (VUVLO-1V).

This prevents the switch working with excessive 'on' resistance under conditions where

the duty cycle is high.

Thermal shutdown protection

To ensure the reliability, the AX2020 is built with a thermal shutdown (TSD) protection

function. The TSD protests the IC from over temperature (150°C). When the chip

temperature decreases (115°C), the IC recovers again.