Rainbow-electronics MAX1712 Uživatelský manuál stáhnout pdf (Strana 11)

BIAS

= I

+ f

+ Q

) = 15mA to 30mA (typ)

where I

is 600µA (typ), f is the switching frequency,

and Q

are the MOSFET data sheet total

gate-charge specification limits at V

= 5V.

Free-Running, Constant-On-Time PWM

Controller with Input Feed-Forward

The Quick-PWM control architecture is an almost fixed-

frequency, constant-on-time current-mode type with volt-

age feed-forward (Figure 2). This architecture relies on

the filter capacitor’s ESR to act as the current-sense

resistor, so the output ripple voltage provides the PWM

ramp signal. The control algorithm is simple: the high-

side switch on-time is determined solely by a one-shot

whose period is inversely proportional to input voltage

and directly proportional to output voltage. Another one-

shot sets a minimum off-time (400ns typ). The on-time

one-shot is triggered if the error comparator is low, the

MAX1710/MAX1711/MAX1712

High-Speed, Digitally Adjusted

Step-Down Controllers for Notebook CPUs

______________________________________________________________________________________ 11

REF

-5%

FROM

D/A

REF

D0 D1 D2 D3

10k

ERROR

AMP

TOFF

TON

REF

+12%

REF

-30%

R-2R

D/A CONVERTER

CHIP SUPPLY

GNDS

SHDN

FBS

PGOOD

OVP/UVLO

LATCH

ON-TIME

COMPUTE

TON

1-SHOT

TRIG

BATT

2V TO 28V

TRIG

REF

GND

REF

PGND

+5V

OUTPUT

ZERO CROSSING

CURRENT

LIMIT

BST

LIM

+5V

5µA

+5V

S2 TIMER

SKIP

OVP

TON

V+

70k

MAX1710

Figure 2. MAX1710 Functional Diagram

1 2 ... 6 7 8 9 10 11 12 13 14 15 16 ... 27 28

MAX1710/MAX1711/MAX1712 1
MAX1710/MAX1711 14

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