Rainbow-electronics MAX1715 Manual de usuario descargar pdf (Pagina 10)

MAX1715

Ultra-High Efficiency, Dual Step-Down

Controller for Notebook Computers

10 ______________________________________________________________________________________

= 5V

BIAS SUPPLY

PINS 15, 23, 28 = N.C.

POWER-GOOD

INDICATOR

MAX1715

OUTPUT1

1.8V

4.5V TO 28V

CMPSH-3A

ILIM1

ON1

DL1

TON

OUT1

AGND

C3 C4

LX1

DH1

0.1µF

0.22µF

FB1

1µF

C11

1µF

BST1

ILIM2

REF

ON1

ON2

DL2

PGND

+5V

100k

OUT2

LX2

DH2

FB2

PGOOD

V+

BST2

SKIP

4.7µF

20Ω

OUTPUT2

2.5V

ON/OFF

CONTROLS

Figure 1. Standard Application Circuit

Standard Application Circuit

The standard application circuit (Figure 1) generates

two low-voltage rails for general-purpose use in note-

book computers (I/O supply, fixed CPU core supply,

DRAM supply). This DC-DC converter steps down a

battery or AC adapter voltage to voltages from 1.0V to

5.5V with high efficiency and accuracy.

See Table 1 for a list of components for common appli-

cations. Table 2 lists component manufacturers.

Detailed Description

The MAX1715 buck controller is designed for low-volt-

age power supplies for notebook computers. Maxim’s

proprietary Quick-PWM pulse-width modulator in the

MAX1715 (Figure 2) is specifically designed for han-

dling fast load steps while maintaining a relatively con-

stant operating frequency and inductor operating point

over a wide range of input voltages. The Quick-PWM

architecture circumvents the poor load-transient timing

problems of fixed-frequency current-mode PWMs while

also avoiding the problems caused by widely varying

switching frequencies in conventional constant-on-time

and constant-off-time PWM schemes.

+5V Bias Supply (V

and V

)

The MAX1715 requires an external +5V bias supply in

addition to the battery. Typically, this +5V bias supply

is the notebook’s 95% efficient +5V system supply.

Keeping the bias supply external to the IC improves

efficiency and eliminates the cost associated with the

+5V linear regulator that would otherwise be needed to

supply the PWM circuit and gate drivers. If stand-alone

capability is needed, the +5V supply can be generated

with an external linear regulator such as the MAX1615.

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