ADP3026(RevPrB) データシートの表示（PDF） - Analog Devices

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ADP3026
(Rev.:RevPrB)

High-Efficiency Notebook Computer Power Supply Controller

Analog Devices 

PRELIMINARY TECHNICAL DATA

ADP3026

Upper MOSFET Duty Cycle= VOUT

VIN

(10)

Lower MOSFET Duty Cycle = VIN – VOUT

VIN

(11)

From the duty cycle, the required minimum RDS(ON) for

each MOSFET can be derived by the following equations:

Upper MOSFET:

RDS(ON )

(Upper )

=

VOUT

×

VIN × PD

I

2

MAX

×

(1

+

α∆T )

(12)

Lower MOSFET:

RDS(ON )

(Lower) =

(VIN

VIN × PD

–

VOUT

)

×

I

2

MAX

×

(1 +

α∆T )

(13)

where PD is the allowable power dissipation and α is the tem-

perature dependency of RDS(ON). PD will be determined by

efficiency and/or thermal requirements (see Efficiency ). (1

+ α∆T) is generally given for a MOSFET in the form of a

normalized RDS(ON) vs. temperature curve, but α = 0.007/°C

can be used as an approximation for low voltage MOSFETs.

Maximum MOSFET power dissipation occurs at maxi-

mum output current, and can be calculated as follows:

Upper MOSFET:

PD (Upper) =

VOUT

VIN

×

I

2

MAX

× RDS(ON)

× (1 +

α∆T )

(14)

Lower MOSFET:

PD (Lower ) =

VIN – VOUT

VIN

×

I

2

MAX

× RDS(ON )

× (1 +

α∆T) (15)

The Schottky diode, D1 shown in Figure 2, conducts only

during the dead time between conduction of the two power

MOSFETs. D1’s purpose is to prevent the body-diode of the

lower N-channel MOSFET from turning on and storing

charge during the dead time, which could cost as much as

1% in efficiency. D1 should be selected for forward voltage of

less than 0.5 V when conducting IMAX. Recommended transis-

tors for upper and lower MOSFET’s are given in Table VII.

Table VII. Recommended MOSFETs

Maximum

Output

Vishay/

Siliconix

International

Rectifier

2A

Si4412DY,

28 mΩ

IRF7805,

11 mΩ

4A

Si4410DY,

13.5 mΩ

IRF7811,

8.9 mΩ

IRF7805,

11 mΩ

10 A

Si4874DY,

7.5 mΩ

IRFBA3803,

5.5 mΩ

IRF7809,

7.5 mΩ

Soft Start

The soft-start time of each of switching regulator can be

programmed by connecting a soft-start capacitor to the corre-

sponding soft-start pin (SS3 or SS5). The time it takes each

regulator to ramp up to its full duty ratio depends propor-

tionally on the values of the soft-start capacitors. The

charging current is 2.5 µA ±20%. The capacitor value to set

a given soft-start time, tSS, is given by:

CSS

≅

2.5µA

×

(tSS )

2.6V

(pF)

(16)

Maximum Output

Current

Input Capacitors

Output Capacitors

+3.3 V Output

Output Capacitors

+5 V Output

Table VI. Recommended Capacitor Manufacturers

2A

TOKIN Multilayer

Ceramic Caps, 22 µF/25 V

P/N: C55Y5U1E226Z

TAIYO YUDEN INC.

Ceramic Caps, Y5V Series

10 µF/25 V

P/N: TMK432BJ106KM

SANYO POSCAP TPC

Series, 68 µF/10 V

SANYO POSCAP TPC

Series, 68 µF/10 V

4A

TOKIN Multilayer

Ceramic Caps, 2 × 22 µF/25 V

P/N: C55Y5U1E226Z

TAIYO YUDEN INC.

Ceramic Caps, Y5V Series

2 ×10 µF/25 V

P/N: TMK432BJ106KM

SANYO POSCAP TPC

Series, 2 × 68 µF/10 V

SANYO POSCAP TPC

Series, 2 × 68 µF/10 V

10 A

TOKIN Multilayer

Ceramic Caps, 2 × 22 µF/25 V

P/N: C55Y5U1E226Z

VISHEY Ceramic Caps,

Z5U Series, 2 × 15 µF/25 V

SANYO POSCAP TPB

Series, 2 × 220 µF/4.0 V

SANYO POSCAP TPB

Series, 2 × 330 µF/6.3 V

REV. PrB

–15–

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