LX1662/62A, LX1663/63A

PRODUCT DA T ABOOK 1996/1997

11

Copyright © 1999

Rev. 1.1 11/99

BILL OF MATERIALS

C

2

1500µF, 6.3V capacitor

MV-GX Sanyo

2

C

1

1500µF, 6.3V capacitor

MV-GX Sanyo

4

C

8

680pF

SMD Cap

1

C

3

0.1µF

SMD Cap

1

C

5

1µF, 16V

SMD Ceramic

1

L

1

5µF Inductor

HM0096832 BI

1

L

2

1µF Inductor

1

Q

1

MOSFET

IRL3102 International Rectifier or equivalent

1

Q

2

MOSFET

IRL3303 International Rectifier or equivalent

1

R

1

2.5mΩ Sense Resistor (PCB trace)

1

U1

Controller IC

LX1662CD Linfinity

1

Total

15

Ref

Description

Part Number / Manufacturer

Qty.

LX1662 Bill of Materials (Refer to Product Highlight)

USING THE LX1662/63

DEVICES

The LX1662/63 devices are very easy to design with, requiring

only a few simple calculations to implement a given design. The

following procedures and considerations should provide effec-

tive operation for virtually all applications. Refer to the Appli-

cation Information section for component reference designa-

tors.

TIMING CAPACITOR SELECTION

The frequency of operation of the LX166x is a function of duty

cycle and OFF-time. The OFF-time is proportional to the timing

capacitor (which is shown as C

this data sheet), and is modulated to minimize frequency

variations with duty cycle. The frequency is constant, during

steady-state operation, due to the modulation of the OFF-time.

The timing capacitor (C

should be selected using the

following equation:

C

Where I

(recommended to be around 200kHz for optimal operation and

component selection).

When using a 5V input voltage, the switching frequency (f

can be approximated as follows:

C

Choosing a 680pF capacitor will result in an operating

frequency of 183kHz at V

When a 12V power input

is used, he capacitor value must be changed (the optimal timing

capacitor for 12V input will be in the range of 1000-1500pF).

L

The inductance value chosen determines the ripple current

present at the output of the power supply. Size the inductance

to allow a nominal ±10% swing above and below the nominal DC

load current, using the equation L = V

OFF-time, V

time, and

∆I is peak-to-peak ripple current in the inductor. Be

sure to select a high-frequency core material which can handle

the DC current, such as 3C8, which is sized for the correct power

level. Typical inductance values can range from 2 to 10µH.

Note that ripple current will increase with a smaller inductor.

Exceeding the ripple current rating of the capacitors could cause

reliability problems.

(1 - V

f

I

DIS

f

S