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Date: 7/12/04

SP6655 High Efficiency 400mA Synchronous Buck Regulator

© Copyright 2004 Sipex Corporation

APPLICATION INFORMATION

Output Voltage Program

The output voltage is programmed by the external

divider, as shown in the typical application circuit

AC voltage seen by the loop comparator since the

internal FB pin capacitance can form a low pass

0.8V

Output Voltage Ripple Frequency

An important consideration in a power supply

application is the frequency value of the output

ripple. Given the control technique of the SP6655

(as described in the operations section), the

frequency of the output ripple will vary when in

light to moderate load in the discontinuous or

PFM mode. For moderate to heavy loads greater

than about 100mA inductor current ripple, (for

the typical 10

µH inductor application on 100mA

is half the 200mA inductor current ripple), the

output ripple frequency will be fairly constant.

From the operations section, this maximum loop

frequency in continuous conduction mode is:

1

*

*

Data for loop frequency, as measured from

output voltage ripple frequency, can be found in

the typical performance curves.

Layout Considerations

Proper layout of the power and control circuits is

necessary in a switching power supply to obtain

good output regulation with stability and a mini-

mum of output noise. The SP6655 application

circuit can be made very small and reside close to

the IC for best performance and solution size, as

long as some layout techniques are taken into

consideration. To avoid excessive interference

between the SP6655 high frequency converter and

the other active components on the board, some

INDUCTORS SURFACE MOUNT

Inductor Specification

Inductance

Manufacturer/Part No.

Series R Ω

I

Size

Inductor Type

Manufacturer

(µH)

LxW(mm)

Ht. (mm)

Website

10

Murata LQH32CN100K11

0.300

0.45

3.2 x 1.6

1.8

Unshielded Ferrite Core murata.com

10

TDK RLF5018T-100MR94

0.056

0.94

5.6 x 5.2

2.0

Shielded Ferrite Core

tdk.com

10

Coilcraft LPO6013-103K

0.300

0.70

6.0 x 5.4

1.3

Unshielded Ferrite Core coilcraft.com

22

Murata LQH32CN220K21

0.710

0.25

3.2 x 1.6

1.8

Unshielded Ferrite Core

murata.com

22

TDK RLF5018T- 220MR63

0.130

0.63

5.6 x 5.2

2.0

Shielded Ferrite Core

tdk.com

22

Coilcraft LPO6013-103

0.520

0.45

6.0 x 5.4

1.3

Unshielded Ferrite Core coilcraft.com

CAPACITORS - SURFACE MOUNT

Capacitor Specification

Capacitance

Manufacturer/Part No.

ESR

RippleCurrent

Size

Voltage

Capacitor Type

Manufacturer

(µF)

Ω (max)

(A) @ 45°C

LxW(mm) Ht. (mm)

(V)

Website

10

TDK C2012X5R0J106M

0.003

1.00

2.0 x 1.2

1.25

6.3

X5R Ceramic

tdk.com

10

Murata GRM21BR60J106KE01

0.003

1.00

2.0 x 1.2

1.25

6.3

POSCAP

murata.com

4.7

TDK C2012X5R0J475M

0.005

1.00

2.0 x 1.2

1.25

6.3

X5R Ceramic

tdk.com

4.7

Murata GRM21BR60J475KE01

0.005

1.00

2.0 x 1.2

1.25

6.3

POSCAP

murata.com

Table 2 Component Selection

Note: Components highlighted in bold are those used on the SP6655 Evaluation Board.