ACE711E

2A, Step-Up DC/DC Regulator 20V

VER 1.2

7

PWM Dimming Control or Output Voltage Programming

When the EN pin is constantly high, the FB voltage is regulated to 200mV typically. However, the EN pin

allows a PWM signal to reduce this regulation voltage; therefore, it achieves LED brightness dimming or

output voltage programming (only to make output voltage lower). The relationship between the duty cycle

and FB voltage is given by Equation 1.3:

VFB =Duty*200 mV

(1.3)

Where

Duty = duty cycle of the PWM signal, 200 mV = internal reference voltage

This PWM dimming eliminates the audible noise which often occurs when the output current is pulsed in

replica of the frequency and duty cycle of PWM control. Unlike other scheme which filters the PWM signal

for analog dimming, ACE711E regulation voltage is independent of the PWM logic voltage level which

often has large variations for optimum performance, use the PWM dimming frequency in the range of

25kHz to 100kHz.

APPLICATION INFORMATION

Inductor Selection

Using an inductor with a smaller inductance value forces discontinuous PWM when the inductor current

ramps down to zero before the end of each switching cycle. This reduces the boost converter’s maximum

output current, causes large input voltage ripple and reduces efficiency. Large inductance value provides

much more output current and higher conversion efficiency. For these reasons, a 4.7μH to 10μH inductor

value range is recommended. A 10μH inductor optimized the efficiency for most application while

maintaining low inductor peak to peak ripple. Below table lists the recommended inductor for the

ACE711E.

Recommended Inductors for ACE711E

Part #

L(uH)

Saturation Curent (mA)

Vendor

SWRH3D16S

4.7-10

>2500

Sunlord

Schottky Diode Selection

A high-speed rectifying Schottky is recommended for ACE711E for maximum efficiency due to its high

switching frequency. The diode average and peak current rating must be larger than the average output

current and peak inductor current to ensure reliability. In addition, the diode’s reverse breakdown voltage

must exceed the open LED protection voltage.

Input and Output Capacitor Selection

The output capacitor is mainly selected to meet the requirements for the output ripple and loop stability.

The output requir

es a capacitor in the range of 10μF to 22μF.