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FAN5332A Rev. 1.0.1

inductor size, cost and overall efficiency is needed to make the

optimum choice.

The inductor saturation current should be rated around 1.5A,

which is the threshold of the internal current limit circuit. This

limit is reached only during the start-up and with heavy load

condition; when this event occurs the converter can shift over in

discontinuous conduction mode due to the automatic turn-off of

the switching transistor, resulting in higher ripple and reduced

efficiency.

Some recommended inductors are suggested in the table

below:

Table 1: Recommended Inductors

Capacitors Selection

For best performance, low ESR input and output capacitors are

placed as close to the IC pins, are recommended for the lower

input and output ripple. The output capacitor voltage rating

suggested in the table below.

Table 2: Recommended Capacitors

Diode Selection

The external diode used for rectification is usually a Schottky

diode. Its average forward current and reverse voltage maxi-

mum ratings should exceed the load current and the voltage at

the output of the converter respectively. A barrier Schottky diode

such as BAT54 is preferred, due to its lower reverse current over

the temperature range.

even with the IC disabled, since the diode can be instantly dam-

aged by the excessive current.

Thermal Shutdown

When the die temperature exceeds 150°C, a reset occurs and

will remain in effect until the die cools to 130°C, at that time the

circuit will be allowed to restart.

Heavy Load Limitations

in steady state at high ambient temperature can increase the

die temperature to the point where the thermal shutdown kicks

in. To prevent this, a limited time operation should be consid-

ered in applications such as a flash LED driver. An operation

time of 0.4Sec. at maximum load, followed by a 3.6Sec. OFF

time ensures stable operation even in the worst case, provided

that the IC heat dissipation is optimized to lower the junction to

ambient thermal resistance.

The external passive components and the layout of the PCB

play an important role in reaching the highest efficiency of the

boost converter. For best results, the data sheet recommenda-

tions regarding external components and PCB layout should be

followed closely.

PCB Layout Recommendations

The inherently high peak currents and switching frequency of

power supplies require careful PCB layout design. Therefore,

use wide traces for high current paths and place the input

capacitor, the inductor, and the output capacitor as close as

possible to the integrated circuit terminals. The resistor divider

that sets the output voltage should be routed away from the

inductor to avoid RF coupling. A two layer PCB with the bottom

layer as ground plane connected to the pin 2 of the IC is recom-

mended. This ground plane acts as an electromagnetic shield to

reduce EMI and parasitic coupling between components.

Figure 5. Recommended PCB Layout

Inductor

Value

Vendor

Part Number

Comment

6.8µH

TDK

SLF7028T6R8M1R3

Low Profile

6.8µH

MURATA

LQ566C6R8M04

High

Efficiency

6.8µH

COOPER

SD414-6R8

Small Size

Capacitor

Value

Vendor

Part Number

10µF

Murata

GRM31CR70J106KA01B

2.2µF

Murata

GRM32RR71E225KC01B