FEB207 - Fairchild Semiconductor

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FEB207-021 User Guide

FAN2103

TinyBuck™ Integrated Synchronous Buck

Evaluation Board

Featured Fairchild Product: FAN2103

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Table of Contents

1. Overview................................................................................................................................... 3

2. Board Configuration ................................................................................................................. 3

3. Power-Up Sequence.................................................................................................................. 3

4. Board Features .......................................................................................................................... 4

4.1. Switching Waveform ...................................................................................................... 4

4.2. Enable / Inhibit................................................................................................................ 4

4.3. Current Limit .................................................................................................................. 4

4.4. Auto-Restart.................................................................................................................... 4

4.5. Switching Frequency....................................................................................................... 4

4.6. Input Voltage................................................................................................................... 4

4.7. Output Voltage................................................................................................................ 5

4.8. Feedback Loop Response................................................................................................ 5

4.9. Connections..................................................................................................................... 5

5. Schematics ................................................................................................................................ 6

6. Bill of Materials........................................................................................................................ 7

7. Assembly Diagram.................................................................................................................... 8

8. PCB Layout............................................................................................................................... 8

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This guide supports the evaluation kit for the FAN2103 TinyBuck™ Integrated

Synchronous Buck. This guide should be used in conjunction with the FAN2103

datasheet, located at Fairchild’s website (www.fairchildsemi.com).

1. Overview

This board provides 1.8VOUT and 0-3A from 8-20VIN at a 500KHz switching rate using

low-cost ceramic output capacitors.

Figure 1. Evaluation Board and Required Connections

2. Board Configuration

 Output Voltage: 1.8V

 Output Current: 0-3A

 Input Voltage: 8-20V

 Frequency: 500KHz

3. Power-Up Sequence

1. Establish connections to test equipment as shown in Figure 1. Use suitable diameter

wires and connectors to avoid excessive voltage drop or temperature rise.

Do not turn on power supplies until all the connections are complete.

2. Verify voltage sources have current limits adequately set to supply the load.

3. Apply VIN before VCC to avoid skipping the soft-start cycle.

4. Apply the desired load current.

This can be done at any time, including before power-up, but it is recommended to

power-up the first time with 0A load to verify proper connections.

To power down, turn off the VCC (5V) supply first.

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4. Board Features

A ground strap is provided near the lower-left corner of the evaluation board to facilitate

oscilloscope probe connections.

4.1. Sw itching Waveform

Connect an oscilloscope probe to test point marked SW to view the switching waveform.

Since the MOSFETs are integrated, gate/drive waveforms cannot be viewed.

4.2. Enabl e / Inhibit

The momentary push-button switch S1 establishes a connection from EN to GND,

inhibiting the FAN2103 when switching ceases and only standby current is consumed.

A new soft-start cycle commences upon release of S1.

4.3. Curr ent Limit

The current limit threshold can be set lower by reducing R9. This feature is useful in

applications where <3A is required, allowing the designer to select passive external

components with lower current ratings.

With R9 open, the FAN2103 enforces a maximum default current limit in excess of 3A.

4.4. Auto-Restart

The board is configured for auto-restart with a delay (C7) that increases linearly with C7.

Refer to the datasheet for auto-restart or latch-off options.

4.5. Sw itching Frequency

Switching frequency is set by R10 (RT). Frequency may be lowered to 200KHz or raised

to >600KHz.

Large changes in frequency may warrant additional component value changes for the

output filter and compensation network.

4.6. Input Vol tage

The demo board is optimized to work with an 8V to 20V input voltage range. For

operating between 3V to 8V, modifications to output filter, compensation network

component values, and R7 need to be made.

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4.7. Output Voltage

The output voltage is determined by the ratio of R1 and R4. For minor output voltage

changes, adjust R4.

Larger VOUT changes may impact output filter and compensation network component

value selection.

4.8. Feedback Loop Response

R5 opens the feedback loop for closed-loop response measurement. Remove R5 and

connect a network analyzer or injection transformer in its place.

4.9. Connections

Be clear about order of connections, notes or cautions, etc.

Include step-by-step, numbered instructions.

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5. Schematics

0.1u

C4

1

2VOUT

J2+

SW

3.3u

L1

62

R3

56p

C1

1

2GND

J2_

SW

390p

C6

1.5

R6

1.0u

C5

PGOOD

2.49K

R1

0

R5

4.7n

C3

FB

COMP

VCC

VIN

VOUT

2.49K

R2

22u

C12

22u

C9 22u

C10 22u

C11

200K

R7

AGND

4.7u

C14

200K

R9

28.7K

R10

20K

R12

2K

R4

PGOOD

VOUT

4.7n

C2

+5V

5V_RTN

1

2VIN

J1+

1

2GND

J1_

4.7u

C15 4.7u

C16

SPG50

3.3n

C8

SW1

0

R13

3.3n

C7

BOOT

RT

18

VIN 3

BOOT 1

SW P1

FB

19

AGND

16

ILIM

17 SW 6

SW 7

SW 8

SW 9

SW 10

SW 11

SW 12

GND P3

GND 21

GND 22

RAMP 25

VIN 5

VIN 4

PIN2 2

VIN P2

COMP

20

EN

14

VCC

15

PGOOD

13

CLK/FPWM

24

GND 23

FAN2103

U1

NC

Figure 2. FAN2103 Evaluation Board Schematic

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6. Bill of Materials

U1 1 IC, FAN2103, ML P5x6 Fairchild FAN2103M

L1 1

3.3µH, 5.4A, 18mΩ Cooper DR74-3R3-R

R1, 2 2 2.49K, 1%, 0603 DigiKey P2.49K H

R3 1

62Ω, 5%, 0603 DigiKey P62 G

R4 1 2.00K, 1%, 0603 DigiKey P2.00K H

R5, 13 3 0Ω, 5%, 0603 DigiKey P0.0 G

R6 1

1.5Ω, 5%, 0805 DigiKey P1.5 A

R7, 9 2 200K, 1%, 0603 DigiKey 200K H

R10 1 30.1K, 1%, 0603 DigiKey P30.1K H

R12 1 10K, 5%, 0603 DigiKey P10K G

C1 1 56pf, 50V, 5%, NPO, 0603 DigiKey PCC560ACV

C2, 3 2 4.7nf, 50V, 10%, X7R, 0603 DigiKey PCC1780

C7, 8 2 3.3nf, 50V, 10%, X7R, 0603 DigiKey PCC1778

C4 1 0.1µf, 16V, 10%, X7R, 0603 DigiKey PCC1762

C5 1 1.0µf, 10V, 10%, X5R, 0805 DigiKey PCC1807

C6 1 390pf, 50V, 10%, X7R, 0603 DigiKey PCC391BV

C9, 10, 11, 12 4 22µf, 6.3V, 20%, X5R, 1206 DigiKey PCC2242

C14, 15, 16 3 4.7µf, 25V, 20%, X5R, 1206 DigiKey PCC2241

J1+, J1-, J2+, J2- 4 Connector, QDM, 0.25", Right Angle DigiKey 4966K

SW1 1 Switch, 1 pole, momentary push DigiKey EG2513

+5V 1 Test Point, Red DigiKey 5000K

5V_RTN 1 Test Point, Black DigiKey 5001K

SW, PGOOD 2 Test Point, White DigiKey 5002K

PCB 1 PCB, TINYBUCK_2A

C18

R8,R11, R14, R15, R16, R17 5 No Load 0603

C13 1 No Load 7343

C19 1 4.7µf, 25V, 20%, X5R, 1206

C17 1 No Load 8x11

Q1 1 No Load SOT23

C, N, CLKIN, CLKOUT 4 No Load Test Point

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7. Assembly Diagram

Figure 3. Assembly Diagram

8. PCB Layout

Figure 4. PCB Layout

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