MAX770EPA View Datasheet(PDF) - Maxim Integrated

Part Name

Description

Manufacturer

MAX770EPA

5V/12V/15V or Adjustable, High-Efficiency, Low IQ, Step-Up DC-DC Controllers

Maxim Integrated 

5V/12V/15V or Adjustable, High-Efficiency,

Low IQ, Step-Up DC-DC Controllers

LBO V15

V12

V5

FB

V+

LBI

MAX773 ONLY

N

N

REF

1.5V

REFERENCE

ERROR

COMPARATOR

ONE-SHOT

Q TRIG

F/F

S

Q

R

ONE-SHOT

LOW-VOLTAGE

OSCILLATOR

TRIG Q

CURRENT-SENSE

AMPLIFIER

DUAL-MODE

COMPARATOR

MAX770–MAX773

200mV

SHDN

BIAS

CIRCUITRY

MAX770

MAX771

MAX772

N

EXT

CONTROL

2.5V

V+

6V

SGND

EXTH

MAX773

ONLY

EXTL

0.2V

0.1V

EXT

MAX770

MAX771

MAX772

CS

Figure 1. Block Diagram

Floating the shunt-regulator ground (SGND) disables

the shunt regulator. To enable it, connect SGND to

GND. The shunt regulator requires 1mA minimum cur-

rent for proper operation; the maximum current must

not exceed 20mA. The MAX773 operates in non-boot-

strapped mode when the shunt regulator is used, and

EXT swings between the 6V shunt-regulator voltage

and GND.

When using the shunt regulator, use an N-channel pow-

er FET instead of an NPN power transistor as the power

switch. Otherwise, excessive base drive will collapse

the shunt regulator.

External Power-Transistor

Control Circuitry

PFM Control Scheme

The MAX770–MAX773 use a proprietary current-limited

PFM control scheme to provide high efficiency over a

wide range of load currents. This control scheme com-

bines the ultra-low supply current of PFM converters (or

pulse skippers) with the high full-load efficiency of

PWM converters.

Unlike traditional PFM converters, the MAX770–

MAX773 use a sense resistor to control the peak induc-

tor current. They also operate with high switching

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