SP6642EU 查看數據表（PDF） - Signal Processing Technologies

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SP6642EU

Single Alkaline Cell, High Efficiency Step-Up DC-DC Converter

Signal Processing Technologies 

It is suggested designers select the largest

inductor value possible that will satisfy the load

requirement and minimize peak switching

current and any resultant noise and voltage

ripple. A closed-core inductor, such as a toroid

or shielded bobbin, will minimize any fringe

magnetic fields or EMI.

from sensitive RF and analog input stages. The

external voltage-feedback network should be

placed very close to the FB pin (within 0.2in or

5mm). Any 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.

APPLICATION NOTES

Printed circuit board layout is a critical part of

design. Poor designs can result in excessive

EMI on the voltage gradients and feedback

paths on the ground planes with applications

involving high switching frequencies and large

peak currents. Excessive EMI can result in

instability or regulation errors.

All power components should be placed on the

PC board as closely as possible with the traces

kept short, direct, and wide (>50mils or 1.25mm).

Extra copper on the PC board should be integrated

into ground as a pseudo-ground plane. On a

multilayer PC board, route the star ground using

component-side copper fill, then connect it to

the internal ground plane using vias.

For the SP6642/6643 devices, the inductor and

input and output filter capacitors should be

soldered with their ground pins as close together

as possible in a star-ground configuration. The

VOUT pin must be bypassed directly to ground as

close to the SP6642/6643 devices as possible

(within 0.2in or 5mm). The DC-DC converter

and any digital circuitry should be placed on the

opposite corner of the PC board as far away

Table 1. Surface-Mount Inductor Information

INDUCTANCE

(µH)

VENDOR/PART

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 22µF, 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.

INDUCTOR SPECIFICATION

RESISTANCE

(Ω)

ISAT

(mA)

68

Coilcraft DO1608-683

0.75

400

Sumida CD54-680

0.46

610

Coilcraft DO1608-104

1.1

310

100

Sumida CD54-101

0.7

520

TDK NLC565050T-101K

1.6

250

Coilcraft DO1608-154

1.7

270

150

Sumida CD54-151

1.1

400

TDK NLC565050T-151K

2.2

210

220

Coilcraft DO1608-224

2.3

220

Sumida CD54-221

1.57

350

Rev. 10-6-00

SP6642/6643 High Efficiency Step-Up DC-DC Converter

14

© Copyright 2000 Sipex Corporation

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