UU28141

CMOS IC

UNISONICTECHNOLOGIESCO.,LTD

4 of 5

www.unisonic.com.tw

QW-R125-040.B



FUNCTION DESCRIPTION

Setting the ILED Current

Application circuit item shows the basic application circuit with UTC UU28141 adjustable output version. The

external resistor sets the LED output current according to the following equation:

REST

20mA

15Ω

6mW

350mA

0.857Ω

105mW

Under Voltage Lockout (UVLO)

To avoid mis-operation of the device at low input voltages an under voltage lockout is included that disables the

device, if the input voltage falls below (2.25V~100mV).

Over Voltage Protection

OVP measure the output voltage for open circuit protection. Connect OVP pin to the output at the top of the LED

Input Capacitor Selection

The input capacitor reduces the surge current drawn from the input and switching noise from the device. The input

capacitor impedance at the switching frequency shall be less than input source impedance to prevent high frequency

switching current passing to the input. A low ESR input capacitor sized for maximum RMS current must be used.

Ceramic capacitors with X5R or X7R dielectrics are highly recommended because of their low ESR and small

temperature coefficients. A 2.2uf ceramic capacitor for most applications is sufficient. For a lower output power

requirement application, this value can be decreased.

Output Capacitor Selection

The output capacitor is required to keep the output voltage ripple small and to ensure regulation loop stability. The

output capacitor must have low impedance at the switching frequency. Ceramic capacitors with X5R or X7R

dielectrics are recommended due to their low ESR and high ripple current. A 1uF ceramic capacitors works for most

of the applications. Higher capacitor values can be used to improve the load transient response.