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AAT1171

600mA Voltage-Scaling Step-Down Converter

for RF Power Amplifiers with Bypass Switch

DATA SHEET

PA Step-Down Converter Design Example

Specifications

2.7V to 4.2V (3.6V nominal)

2.0MHz

85°C

Output Inductor

L1 = 2.2μH

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

2.1

V

2.1V

⋅ 1 -

=

⋅ 1 -

= 239mA

2.2µH ⋅ 2.0MHz

4.2V

⎛

⎝

⎞

⎠

⎛

⎝

⎞

⎠

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

I

= 0.6A + 0.118A = 0.718A

2

P

2

Output Capacitor

1

23

1

3.4V · (4.2V - 3.4V)

4.7µH · 2.0MHz · 4.2V

23

RMS

I

=

·

·

3 · 0.6A

0.2V · 2.0MHz

=

= 4.5µF

·

= 69mArms

·

Input Capacitor

=

= 3.4µF

1

⎛⎞

- ESR ·

⎝⎠

1

⎛⎞

- 5mΩ ·

⎝⎠

25mV

0.6A

RMS

I

2

=

= 0.3Arms