UC3550L-33-AF5-R datasheet(7/10 Pages) UTC

7 / 10 page

UC3550

CMOS IC

UNISONICTECHNOLOGIESCO.,LTD

7 of 10

www.unisonic.com.tw

QW-R502-082,A

EXTERNAL COMPONENT SELECTION

Inductor Selection

An inductor value of 10uH performs well in most application. The UC3550 series also work with inductors in the

4.7uH to 12uH range. An inductor with higher peak inductor current tends a higher output voltage ripple（IPEAK x

output filter capacitor ESR）. The inductor’s DC resistance significantly affects efficiency.

Output Capacitor Selection

The output ripple voltage（IPEAK x output filter capacitor ESR）is the product of the peak inductor current and the

output capacitor Equivalent Series Resistance (ESR). Best performances are obtained with good high frequency

characteristics capacitors and low ESR. The best compromise for the value of the Output Capacitance is 220F

Tantalum Capacitor. The output capacitor as close as possible to the device pins.

Input Capacitor Selection

The Input Capacitor is required to compensate, if present, the series impedance between the Supply Voltage

Source and the Input Voltage of the Application. A value of 10 F is enough to guarantee stability

for distances less

than 2". In any case we suggest to connect both capacitors, The input capacitor as close as possible to the device

pins.

Diode Selection

The Schottky diode with an high switching speed and a very low Forward Voltage (VF) is needed. Higher VF may

cause lost power as heat in the diode, with a decrease of the Efficiency. Moreover, since the Output Voltage pin is

also used as the device Supply Voltage, the Start-up Voltage (see related plots) is strictly due to the diode Forward

Voltage at the rated Forward Current.

External Component Selection

An enhancement N-channel MOSFET or a bipolar NPN transistor can be used as the external switch transistor.

since enhancement N-channel MOSFET is a voltage driven device, it is a more efficient switch than a BJT transistor.

However, he MOSFET requires a higher voltage to turn on as compared with BJT transistor

For enhancement N-channel MOSFET ( it is especially importance for RDS(ON),typically<0.1Ω, threshold voltage,

VGS(TH) must be<VOUT, typically<1.5V.

For bipolar NPN transistor, continuous collector current typically 1A to 4A and VCE(SAT)<0.2V. the driving capability

is determined by the DC current gain, HFE, of the transistor and the base resistor, Rb. Moreover, a speed-up

capacitor, Cb should be connected in paralled with Rb to reduce switch loss and improve efficiency.

UC3550L-33-AF5-R 数据表(PDF) 7 Page - Unisonic Technologies

UC3550L-33-AF5-R 数据表(HTML) 7 Page - Unisonic Technologies

Html Pages

1 2 3 4 5 6 7 8 9 10

数据表下载