SP6644 datasheet(12/15 Pages) SIPEX

12 / 15 page

Date: 11/30/04

SP6644/6645 High Efficiency Boost Regulator

noisy traces, such as from the LX pin, should be

kept away from the voltage-feedback network

and separated from it using grounded copper to

minimize EMI.

Capacitor equivalent series resistance is a major

contributor to output ripple, usually greater than

60%. Low ESR capacitors are recommended.

Ceramic capacitors have the lowest ESR.

Low-ESR tantalum capacitors may be a more

acceptable solution having both a low ESR and

lower cost than ceramic capacitors. Designers

should select input and output capacitors with a

rating exceeding the peak inductor current. Do

not allow tantalum capacitors to exceed their

ripple-current ratings. A 22

µF, 6V, low-ESR,

surface-mount tantalum output filter capacitor

typically provides 60mV output ripple when

stepping up from 1.3V to 3.3V at 20mA.

An input filter capacitor can reduce peak

currents drawn from the battery and improve

efficiency. Low-ESR aluminum electrolytic

capacitors are acceptable in some applications

but standard aluminum electrolytic capacitors

are not recommended.

Designers should add LC pi filters, linear

post-regulators, or shielding in applications

necessary to address excessive noise, voltage

ripple, or EMI concerns. The LC pi filter's cutoff

frequency should be at least a decade or two

below the DC-DC converters's switching

frequency for the specified load and input voltage.

A small SOT23-5pin 200mA Low Drop Out

linear regulator can be used at the SP6644/6645

output to reduce output noise and ripple. The

schematic in figure 29 illustrates this circuit with

the SP6644 3.3V output followed by the Sipex

SP6201 3.0V output Low Drop Out linear regu-

lator. Compare in Figure 21 the SP6644 ripple of

40-50mVpp with the SP6201 ripple of about

3mVpp and you can see the amount of noise

reduction obtained.

Additional performance

characteristics for the SP6644/6201 combina-

tion can be seen in figures 17 to 20.

Table 1. Surface-Mount Inductor Information

Inductor Specification

Inductance

Manufacturer/Part No.

Resistance

Isat

(uH)

(ohms)

(mA)

Sumida CD43-220

0.38 (max)

680

Sumida CDRH5D18-220

0.28 (max)

760

Coilcraft DO1608C-223

0.32 (typ)

700

Sumida CD43-470

0.84 (max)

440

Coilcraft DO1608C-473

0.56 (typ)

500

100

Sumida CD54-101

0.7 (max)

520

Coilcraft DO1608C-104

1.1(typ)

310

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