MAX863EEE Ver la hoja de datos (PDF) - Maxim Integrated

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MAX863EEE

Dual, High-Efficiency, PFM, Step-Up DC-DC Controller

Maxim Integrated 

Dual, High-Efficiency, PFM, Step-Up

DC-DC Controller

FB2

REF

CS2

100mV

CS1

SENSE1 VDD - 100mV

FB1

100mV

LBO

REF

LBI

ERROR

COMPARATOR

CURRENT-SENSE

COMPARATOR

Q

TRIG

MAX ON-TIME

ONE-SHOT

TRIG

Q

MIN ON-TIME

ONE-SHOT

S

Q

R

TIMING

BLOCK

100mV

CURRENT-

SENSE

COMPARATOR

LOW-

VOLTAGE

OSCILLATOR

TIMING

BLOCK

REF

ERROR

COMPARATOR

N

N

VDD

REF

1.25V

BIAS

MAX863

EXT2

UVLO

PGND

BOOT

EXT1

VDD

Figure 1. Functional Diagram

GND

REF

SHDN2 SHDN1

The flip-flop resets and turns off the MOSFET when

either a) the voltage across the current-sense resistor

exceeds 100mV, or b) the 17.5µs maximum on-time

one-shot trips. When the MOSFET turns off, the mag-

netic field begins to collapse, and forces current into

the output capacitor and load. As the stored energy is

transferred to the output, the inductor current ramps

down. The output capacitor smoothes out the energy

transfer by storing charge when the diode current is

high, then supplying current to the load during the first

half of each cycle, maintaining a steady output voltage.

Resetting the flip-flop sets the off-time one-shot, dis-

abling the error-comparator output and forcing the

MOSFET off for at least 2µs to enforce a minimum time

for energy transfer to the output. The MAX863 waits

until the output voltage drops again before beginning

another cycle. The MAX863’s switching frequency

depends on the load current and input voltage.

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