AAT1106 データシートの表示（PDF） - Advanced Analogic Technologies

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AAT1106

600mA Step-Down Converter

Advanced Analogic Technologies 

IQ is the step-down converter quiescent current.

The term tsw is used to estimate the full load step-

down converter switching losses.

For the condition where the step-down converter is

in dropout at 100% duty cycle, the total device dis-

sipation reduces to:

PTOTAL = IO2 · RDSON(HS) + IQ · VIN

Since RDS(ON), quiescent current, and switching

losses all vary with input voltage, the total losses

should be investigated over the complete input volt-

age range. Given the total losses, the maximum

junction temperature can be derived from the θJA

for the TSOT23-5 package which is 150°C/W.

TJ(MAX)

=

PTOTAL

·

Θ

JA

+

TAMB

Layout Guidance

When laying out the PC board, the following steps

should be taken to ensure proper operation of the

AAT1106. These items are also illustrated graphi-

cally in Figure 3.

AAT1106

600mA Step-Down Converter

1. The power traces (GND, LX, IN) should be kept

short, direct, and wide to allow large current

flow. Place sufficient multiply-layer pads when

needed to change the trace layer.

2. The input capacitor (C1) should connect as

closely as possible to IN (Pin 4) and GND (Pin 2).

3. The output capacitor C3 and L1 should be con-

nected as closely as possible. The connection

of L1 to the LX pin should be as short as pos-

sible and there should not be any signal lines

under the inductor.

4. The feedback FB trace or OUT pin (Pin 5) should

be separate from any power trace and connect

as closely as possible to the load point. Sensing

along a high-current load trace will degrade DC

load regulation. If external feedback resistors are

used, they should be placed as closely as possi-

ble to the FB pin (Pin 5) to minimize the length of

the high impedance feedback trace.

5. The resistance of the trace from the load return

to the GND (Pin 2) should be kept to a minimum.

This will help to minimize any error in DC regu-

lation due to differences in the potential of the

internal signal ground and the power ground.

1106.2007.07.1.0

15

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