AAT1171 View Datasheet(PDF) - Analog Technology Inc

Part Name

Description

MFG CO.

AAT1171

600mA Voltage-Scaling Step-Down Converter for RF Power Amplifiers with Bypass Switch

Analog Technology Inc 

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AAT1171

600mA Voltage-Scaling Step-Down Converter

for RF Power Amplifiers with Bypass Switch

PA Step-Down Converter Design Example

Specifications

VO(BUCK) 0.6V to 3.4V with RL =10Ω

VIN

2.7V to 4.2V (3.6V nominal)

FS

2.0MHz

TAMB 85°C

Output Inductor

L1 = 2.2µH

For Copper Electronics SD3112, 2.2µH, DCR = 140mΩ.

ΔIL1(MAX) =

VO

L ⋅ FS

⋅

⎛⎝1

-

VO ⎞

VIN ⎠

=

2.1V

2.2µH ⋅ 2.0MHz

⋅

⎛⎝1

-

2.1V ⎞

4.2V⎠

= 239mA

The maximum inductor ripple current occurs at 50% duty cycle at the maximum input voltage.

IPKL1

=

IO

+

ΔIL1(MAX)

2

=

0.6A

+

0.118A

=

0.718A

PL1 = IO2 ⋅ DCR = 0.6A2 ⋅ 140mΩ = 50mW

Output Capacitor

Specify that VDROOP = 0.2V for a 600mA load pulse.

COUT

=

3 · ΔILOAD

VDROOP · FS

=

3 · 0.6A

0.2V · 2.0MHz

= 4.5µF

IRMS

=

1 · (VO) · (VIN(MAX) - VO) = 1

2· 3 L1 · FS · VIN(MAX) 2· 3

· 3.4V · (4.2V - 3.4V)

4.7µH · 2.0MHz · 4.2V

= 69mArms

PESR = ESR · IRMS2 = 5mΩ · (69mA)2 = 24µW

20

1171.2007.08.1.1

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