FAN5350(2007) データシートの表示（PDF） - Fairchild Semiconductor

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FAN5350
(Rev.:2007)

3MHz, 600mA Step-Down DC-DC Converter in Chip-Scale and MLP Packaging

Fairchild Semiconductor 

PCB Layout Guidelines

For the bill of materials of the FAN5350 evaluation

board, see Table 1. There are only three external

components: the inductor and the input and output

capacitors. For any buck switcher IC, including the

FAN5350, it is always important to place a low-ESR

input capacitor very close to the IC, as shown in Figure

7. That ensures good input decoupling, which helps

reduce the noise appearing at the output terminals and

ensures that the control sections of the IC do not

behave erratically due to excessive noise. This reduces

switching cycle jitter and ensures good overall

performance. It is not considered critical to place either

the inductor or the output capacitor very close to the IC.

There is some flexibility in moving these two

components further away from the IC.

Description

Qty.

Ref.

Vendor

Part Number

1.2μH, 1.8A, 55mΩ

TOKO

1117AS-1R2M

Inductor

1.3μH, 1.2A, 90mΩ 1

L1

FDK

MIPSA2520D1R0

1.5μH, 1.3A

Taiyo Yuden

CBC3225T15MR

Capacitor 4.7μF, ±10%, 6.3V, X5R, 0603 2

CIN,COUT

MURATA GRM39 X5R 475K 6.3

IC DC/DC Regulator in CSP, 5 bumps

1

U1

Fairchild

FAN5350UCX

Load Resistor (Optional)

1

RLOAD

Any

Table 2. FAN5350 Evaluation Board Bill of Materials (optional parts are installed by request only)

Figure 7. The FAN5350 Evaluation Board PCB (CSP)

Feedback Loop

One key advantage of the non-linear architecture is that

there is no traditional feedback loop. The loop response

to changes in VOUT is essentially instantaneous, which

explains its extraordinary transient response. The

absence of a traditional, high-gain compensated linear

loop means that the FAN5350 is inherently stable over a

wide range of LOUT and COUT.

LOUT can be reduced further for a given application,

provided it is confirmed that the calculated peak current

for the required maximum load current is less than the

minimum of the closed-loop current limit. The advantage

is that this generally leads to improved transient

response, since a small inductance allows for a much

faster increase in current to cope with any sudden load

demand.

The inductor can be increased to 2.2µH; but, for the

same reason, the transient response gets slightly

degraded. In that case, increasing the output capacitor

to 10µF helps significantly.

© 2007 Fairchild Semiconductor Corporation

FAN5350 Rev. 1.0.1

8

www.fairchildsemi.com

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