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Date: 7/20/05

SP7648 Ultra-low Quiescent Current, High Efficiency Boost Regulator

© Copyright 2005 Sipex Corporation

For the example, a 10µH inductor would

have an inductor current ripple of 350mA,

while a 4.7µH inductor would have an in-

ductor current ripple value of 740mA. Do not

allow tantalum capacitors to exceed their

ripple-current ratings. An input filter capaci-

tor can reduce peak currents drawn from

the battery and improve efficiency. For

most applications, use the same capacitor

for the input and output.

Low-ESR tantalum capacitors are accept-

able provided they meet the ESR require-

ment of 0.2Ω to 0.3Ω.

In selecting an

inductor, the saturation current specified for

the inductor needs to be greater than the

SP7648 peak current to avoid saturating

the inductor, which would result in a loss of

efficiency and could damage the inductor.

The SP7648 evaluation board uses a Wurth

and a DCR of 0.065Ω, which handles the

high efficiencies. Other inductors could be

THEORY OF OPERATION

The SP7648 can be programmed as either

a voltage source or a current source. To

program the SP7648 as voltage source, the

SP7648 requires 2 feedback resistors R1 &

in the voltage mode, use the equation:

_______________________ USING THE

The peak inductor current is defined by:

The saturation current specified for the in-

ductor needs to be greater than the peak

INDUCTORS - SURFACE MOUNT

Inductor Specification

Inductance

Manufacturer/Part No.

Series R

Isat

Size LxWxH

Inductor Type

Manufacturer

(uH)

ohms

(A)

(mm)

Website

4.7

Wurth Elektronik 744042004

0.070

1.70

4.8x4.8x1.8

Shielded Ferrite Core

www.we-online.de

4.7

TDK SLF6025T-4R7M1R5-PF

0.031

1.50

6.0x6.0x2.5

Shielded Ferrite Core

www.tdk.com

4.7

Coilcraft MSS6122-4R7MX

0.065

1.85

6.1x6.1x2.2

Shielded Ferrite Core

www.coilcraft.com

6.8

Wurth Elektronik 744042006

0.080

1.50

4.8x4.8x1.8

Shielded Ferrite Core

www.we-online.de

6.8

TDK SLF6025T-6R8M1R3-PF

0.044

1.30

6.0x6.0x2.5

Shielded Ferrite Core

www.tdk.com

6.8

Coilcraft MSS6122-6R8MX

0.100

1.45

6.1x6.1x2.2

Shielded Ferrite Core

www.coilcraft.com

CAPACITORS - SURFACE MOUNT

Capacitor Specification

Capacitance

Manufacturer/Part No.

ESR

Ripple Current

Size LxWxH

Voltage

Capacitor

Manufacturer

(uF)

ohms (max)

10C Rise (A)

(mm)

(V)

Type

Website

10

TDK C2012X5R0J106M

0.020

1.70

2.0x1.2x1.35

6.3

X5R Ceramic

www.tdk.com

10

Murata GRM21BR60J106KE19L

0.020

1.70

2.0x1.2x1.35

6.3

X5R Ceramic

www.murata.com

MOSFETS - SURFACE MOUNT

MOSFET Specification

MOSFET

Manufacturer/Part No.

RDS(on)

Id

Package

Manufacturer

type

ohms

(A)

Size

Website

NMOS

Vishay Si1400DL

0.190

1.70

SC70-6

www.vishay.com

NMOS

Fairchild FDN337N

0.070

2.20

SOT23-3

www.fairchildsemi.com

RESISTORS - LOW VALUE SURFACE MOUNT

Resistor Specification

Resistor

Manufacturer/Part No.

Resistance

Pd

Package

Manufacturer

Ref. Des.

ohms

(W)

Size

Website

Rc, R2

Vishay CRCW0603R33F

0.33

0.10

0603

www.vishay.com

Rc, R2

Vishay CRCW0603R22F

0.22

0.10

0603

www.vishay.com

Note: Components highlighted in bold are those used on the SP7648EB Evaluation Board.

30V, Vgs = 2.5V, Pd = 0.5W

MOSFET

Specifications

20V, Vgs = 2.5V, Pd = 0.5W

Resistor

Specifications

Thick Film 1% or 5%

Thick Film 1% or 5%

Table 1: Component Selection