Rainbow-electronics MAX1625 Bedienungsanleitung PDF herunterladen (Seite 13)

MAX1624/MAX1625

High-Speed Step-Down Controllers with

Synchronous Rectification for CPU Power

______________________________________________________________________________________ 13

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,

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

REF

REF4

AGND

REF3

REF2

REF

FB D0–D4 PWROK PDRV NDRV

CC2

CC1

REF1

10k

40k

WINDOW

CONTROL AND

DRIVE LOGIC

OSCILLATOR

SLOPE

COMPENSATION

REF

AGND

FREQ

REF

REF1 REF2 REF3 REF4

CSL

CSH

BST

RESET

SET

PGND

MAX1624

Figure 3. MAX1624 Simplified Block Diagram

1 2 ... 8 9 10 11 12 13 14 15 16 17 18 ... 23 24

MAX1624/MAX1625 1

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