ACE77LE9

High Efficiency Low Noise PFM Step-Up DC/DC Converter

VER 1.1

6

Application Information LED Current Control

The ACE77LE9 regulates the LED current by setting the current sense resistor (R1) connecting to

feedback and ground. The ACE77LE9 feedback voltage (VFB) is 0.20V. The LED current (ILED) can be

set by a resistor R1. ILED=0.20/R1. In order to have an accurate LED current, a precision resistor is

preferred (1% is recommended).

PWM Dimming Control

When adding the PWM signal to CE pin, the ACE77LE9 is turned on or off by the PWM signal, so the

LEDs operate at either zero or full current. The average LED current increase proportionally with the duty

cycle of the PWM signal. The magnitude of the PWM signal should be higher than the maximum enable

voltage of EN pin, in order to let the dimming control perform correctly. The recommended frequency

range of the PWM signal is from 100Hz to 100 kHz.

Inductor Selection

The recommended val

ue of inductor is 2.2μH to 10μH. Small size and better efficiency are the major

concerns for portable device, such as ACE77LE9 used for mobile phone. The inductor should have low

core loss at 2MHz and low DCR for better efficiency. To avoid inductor saturation current rating should be

considered.

Capacitor Selection

Input and output ceramic capacitors of 4.7μF are recommended for ACE77LE9 applications. For better

voltage filtering, ceramic capacitors with low ESR are recommended. X5R and X7R types are suitable

because of their wider voltage and temperature ranges.

Diode Selection

Schottky diode is a good choice for ACE77LE9 because of its low forward voltage drop and fast reverses

recovery. Using Schottky diode can get better efficiency. The high speed rectification is also a good

characteristic of Schottky diode for high switching frequency. Current rating of the diode must meet the

root mean square of the peak current and output average current multiplication as following:

ID(RMS)

≈(IOUT×IPEAK )1/2

The diode’s reverse breakdown voltage should be larger than the output voltage. SS0520 is

recommended Schottky diode for rectifier.

Layout Guide



A full GND plane without gap break.



Minimized LX node copper area to reduce EMI.



Minimized FB node copper area and keep far away from noise sources.