L5101

LINEAR INTEGRATED CIRCUIT

UNISONICTECHNOLOGIESCO.,LTD

6 of 10

www.unisonic.com.tw

QW-R103-026.B

APPLICATION INFORMATION

Recommended Component Selection

* Inductor Selection: A 10μH inductor is recommended for most applications.

* Capacitor Selection: The small size of ceramic capacitor makes it ideal for UTC L5101 applications, X5R and X7R

types are recommended because of their stable characteristics, 1μF input capacitor with 1μF

output capacitor is sufficient for most UTC L5101 applications.

* Diode Selection: Schottky diode, for its low forward voltage drop and fast reverse recovery, is an ideal choice for

the UTC L5101 diode. A Schottky diode rated 100mA to 200mA is sufficient for most UTC L5101

applications, and the higher current rating usually have larger diode capacitance which can

cause significant switching losses at the 1.2MHz switching frequency.

LED Current Control

* Feedback reference voltage: 95mV.

Open-Circuit Protection

The OVP(Over Voltage Protection) protects the voltage lower than its maximum level under the open circuit

condition, which is caused by the failure or disconnection of the LEDs. The above undesired fault conditions will

cause the feedback voltage falling to 0V, then the UTC L5101 increases duty circle resulting in a high voltage in SW

pin.

Dimming Control

There are three different ways of dimming control circuits as follows:

1. Using a PWM signal

SW

GND

L1

10µH

SHDN

OVP

FB

UTC L5101

C1

1µF

4.7Ω

C2

1µF

D1

R2

R1

51K

1K

PWM

Fig. 2 Dimming Control Using a PWM Signal

Fig. 3 Dimming Control with a PWM Signal