SP6650EUSLASHTR datasheet(12/17 Pages) SIPEX

12 / 17 page

Date: 5/25/04

SP6650 High Efficiency 600mA Synchronous Buck Regulator

TABLE 1.

DESIGNATION

DESCRIPTION

MANUFACTURER

PART NUMBER

COMMENTS

22µH/0.77Arms/0.104DCR

TDK

SLF7030T-220MR86

SHIELDED

INDUCTOR

22µH/1.1Arms/0.071DCR

MURATA

LQS66C220M04

22µH/0.095DCR

SUMIDA

CDRH6D28

SHIELDED

47µH/0.76Arms/0.15DCR

MURATA

LQS66C470M04

SHIELDED

47µH/0.72Arms/0.37DCR

SUMIDA

CR54

C2, C3

47µF/350mΩ/500mA

NEMCO

LSR47/10C-350

INPUT, OUTPUT 47µF/350mΩ/500mA

AVX

TPSC476010R0350

FILTER

33µF/375mΩ/542mA

AVX

TPSC336010R0375

CAPACITORS

22µF/700mΩ/348mA

AVX

TPSB226010R0700

R2,R3

100K/63mW/1%Tolerance

Any approved

Any Package:

10/63mW/5%Tolerance

0402,0505,0603 etc.

The schematic and description is shown in Ad-

ditional Application Circuits.

Another function of the output capacitor is to

hold up the output voltage during the load tran-

sient, and thus prevent excessive overshoot and

undershoot. For that, the recommended capaci-

tor value is greater than 22uF.

An input capacitor can reduce the peak current

drawn from the battery, improve efficiency, and

significantly reduce high frequency noises in-

duced by a switching power supply. The appli-

cable capacitors are tantalum, electrolytic and

ceramic capacitors. An RC filter is recommended

on the Vin pin (pin 2) to effectively cut down the

noise which can impact the IC control circuit.

The time constant of the RC filter needs to be at

least 5 times higher than the switching period,

calculated as 1/FLP during CCM.

APPLICATION INFORMATION

Output Voltage Program

The output voltage can be programmed by the

external voltage divider as shown on page 1.

First pick a resistor value less than 100k for R3.

A large R3 value would reduce the AC voltage

seen by the loop comparator because the FB pin

capacitance (can be as high as 10pF) can form a

low pass filter with R3 paralleling with R2. Lack

of AC voltage to the loop comparator would

give rise to pulse jittering and higher output

ripple. Once the R3 value is picked, R2 can be

calculated from

R2 =

(VOUT -1)R

VREF

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