MAX1714(1999) 데이터 시트보기 (PDF) - Maxim Integrated

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MAX1714
(Rev.:1999)

High-Speed Step-Down Controller for Notebook Computers

Maxim Integrated 

High-Speed Step-Down Controller

for Notebook Computers

IN

2V TO 28V

V+

ILIM

TON

ON-TIME FROM

COMPUTE OUT

TON

TRIG

Q

1-SHOT

SKIP

REF

SHDN

MAX1714A ONLY

REF

REF

-6%

+12%

PGOOD

OVP/UVLO

LATCH

S1

S2

Q

TOFF

1-SHOT

Q

TRIG

MAX1714

+5V

9R

R

BST

SQ

R

ERROR

AMP

REF

-30%

TIMER

CURRENT

DH

LIMIT

Σ

LX

S

Q

R

x2

ZERO CROSSING

VDD +5V

DL

(MAX1714B ONLY)

PGND

(GND)

OUT

CHIP

VCC

SUPPLY

FEEDBACK

MUX

(SEE FIGURE 9)

2V REF

REF

(GND)

AGND

FB

OUTPUT

+5V

NOTE: IN THE MAX1714B, AGND AND PGND ARE INTERNALLY CONNECTED TO THE GND PIN.

( ) ARE FOR THE MAX1714B ONLY.

Figure 2. MAX1714 Functional Diagram

On-Time One-Shot (TON)

The heart of the PWM core is the one-shot that sets the

high-side switch on-time. This fast, low-jitter, adjustable

one-shot includes circuitry that varies the on-time in

response to battery and output voltage. The high-side

switch on-time is inversely proportional to the battery

voltage as measured by the V+ input, and proportional

to the output voltage. This algorithm results in a nearly

constant switching frequency despite the lack of a fixed-

frequency clock generator. The benefits of a constant

switching frequency are twofold: first, the frequency can

be selected to avoid noise-sensitive regions such as the

455kHz IF band; second, the inductor ripple-current

operating point remains relatively constant, resulting in

easy design methodology and predictable output volt-

age ripple.

On-Time = K (VOUT + 0.075V) / VIN

______________________________________________________________________________________ 11

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