MAX1625 Просмотр технического описания (PDF) - Maxim Integrated

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MAX1625

High-Speed Step-Down Controllers with Synchronous Rectification for CPU Power

Maxim Integrated 

High-Speed Step-Down Controllers with

Synchronous Rectification for CPU Power

REF

AGND

VCC

REF

REF1

REF2

REF3

REF4

MAX1624

SLOPE

COMPENSATION

FREQ

OSCILLATOR

CC1

CC2

REF

40k

10k

RESET

Q

REF

CONTROL AND

DRIVE LOGIC

Q

SET

WINDOW

REF2

REF1

REF3

REF4

5

N

AGND

CSL

CSH

LG

BST

DH

LX

VDD

DL

PGND

FB

D0–D4

Figure 3. MAX1624 Simplified Block Diagram

across the current-sense resistor (R1). When the induc-

tor current ramps up to the current-sense threshold, the

MOSFET turns off and interrupts the flow of current from

the supply. This causes the magnetic field in the induc-

tor to collapse, resulting in a voltage surge that forces

the rectifier diode (D1) or MOSFET body diode (N2) on

and keeps the inductor current flowing in the same

amplitude and direction. At this point, the synchronous

rectifier MOSFET turns on until the end of the cycle to

reduce conduction losses across the rectifier diode.

The current through the inductor ramps back down,

PWROK

PDRV

NDRV

transferring the stored energy to the output filter capac-

itor and load. The output filter capacitor stores energy

when inductor current is high and releases it when

inductor current is low, smoothing the voltage delivered

to the load.

The MAX1624/MAX1625 use a current-mode pulse-

width-modulation (PWM) control scheme (Figures 3

and 4). The output voltage is regulated by switching at

a constant frequency and then modulating the peak

inductor current to change the energy transferred per

pulse and to adjust to changes in the load. The output

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