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AAT1150

1MHz 1A Step-Down DC/DC Converter

Advanced Analogic Technologies 

AAT1150

1MHz 1A Step-Down DC/DC Converter

Design Example

Specifications

IOUT = 1.0A

IRIPPLE = 30% of Full Load at Max VIN

VOUT = 1.5V

VIN = 2.7V to 4.2V (3.6V nominal)

Fs = 830kHz

Maximum Input Capacitor Ripple

IRMS = IO ⋅

VO

VIN

⋅ ⎛⎝1-

VO ⎞

VIN⎠

=

IO

2

= 0.5ARMS, VIN = 2 × VO

P = ESRCOUT ⋅ IRMS2 = 5mΩ ⋅ 0.52 A = 1.25mW

Inductor Selection

L

=

VOUT

IO ⋅ k ⋅

F

⋅

⎛⎝1

-

VOUT⎞

VIN ⎠

=

1.0A

⋅

1.5V

0.3 ⋅

830kHz

⋅ ⎛⎝1 -

1.5V ⎞

4.2V⎠

= 3.9µH

Select Sumida inductor CDRH5D18, 4.1µH, 57mΩ, 2.0mm height.

∆I =

VO

L⋅F

⋅

⎛⎝1

-

VO

VIN

⎞

⎠

=

1.5V

4.1µH ⋅ 830kHz

⋅

⎛

⎝1-

1.5V ⎞

4.2V⎠

= 280mA

IPK

=

IOUT

+

∆I

2

=

1.0A

+

0.14A

=

1.14A

P = IO2 ⋅ DCR = 57mW

Output Capacitor Dissipation

IRMS

=

1

2⋅

⋅

3

VOUT ⋅ (VIN - VOUT)

L ⋅ F ⋅ VIN

=

1

2⋅

⋅ 1.5V ⋅ (4.2V - 1.5V)

3 4.1µH ⋅ 830kHz ⋅ 4.2V

= 82mARMS

PESR = ESRCOUT ⋅ IRMS2 = 5mΩ ⋅ 0.0822A = 33µW

14

1150.2005.03.1.2

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