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MA5603

Major Power Technology Co., Ltd.

Rev.1.4

Aug 24, 2016

Inductor Selection

The inductor is required to supply constant current to the output load while being driven

by the switched input voltage. A larger value inductor will result in less ripple current that will

result in lower output ripple voltage. However, the larger value inductor will have a larger

physical size, higher series resistance, and/or lower saturation current. A good rule for

determining the inductance to use is to allow the peak-to-peak ripple current in the inductor to

be approximately 30% of the maximum switch current limit.

VIN

<28V

<35V

Inductor

22uH

33uH

The choice of which style inductor to use mainly depends on the price vs. size

requirements and any EMI requirements.

Analog and Digital Dimming

There are two methods to control dimming for the MA5603 during normal operation. The

first method uses DC voltage to control the feedback voltage. This is shown in Figure 1. As the

DC voltage increases, current starts flowing down R1, R6 and RSET. The loop will continue to

regulate the feedback voltage to 0.22V. Thus the current has to decrease through the LEDs by

the same amount of current as is being injected from the DC voltage source. With a VDC from

0V to 3.6V, the resistor values shown for R1 and R6 can control the LED current from 0mA to

1.5A.

Figure 1 - Dimming Control Using a DC Voltage

If the PWM signal is above 1KHz~100KHz, dimming can be achieved using the circuit

shown in Figure 2 (The LED current from 0mA to 0.33A).

SW

FB

μH

C2

10

μF

16V

MA5603

RSET

0.66Ω

D1

B240

R1

4.7K

R6

75K

VDC

0~3.6V

R7

10K

C7

100nF

PWM

option

Figure 2 - Dimming Control Using a Filtered PWM Signal