MAX756 データシートの表示（PDF） - Maxim Integrated

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MAX756

3.3V/5V/Adjustable-Output, Step-Up DC-DC Converters

Maxim Integrated 

MAX756/MAX757

3.3V/5V/Adjustable-Output,

Step-Up DC-DC Converters

R3

R4

C3

0.1μF

VIN

C1

150μF

5

LBI

8

LX

MAX757 OUT 6

1

SHDN

3

REF

GND

7

2

FB

4

LBO

L1

22μH

D1

1N5817

R1

R2

VOUT

C2

100μF

Figure 1. Standard Application Circuit

where VIN is the desired threshold of the low-battery

detector, R3 and R4 are the input divider resistors at

LBI, and VREF is the internal 1.25V reference.

Since the LBI current is less than 100nA, large resistor

values (typically 10kΩ to 200kΩ) can be used for R3

and R4 to minimize loading of the input supply.

When the voltage at LBI is below the internal threshold,

LBO sinks current to GND. A pull-up resistor of 10kΩ

or more connected from LBO to VOUT can be used

when driving CMOS circuits. Any pull-up resistor con-

nected to LBO should not be returned to a voltage

source greater than VOUT. When LBI is above the

threshold, the LBO output is off. The low-battery com-

parator and reference voltage remain active when the

MAX756/MAX757 is in shutdown mode.

If the low-battery comparator is not used, connect LBI

to VIN and leave LBO open.

Inductor Selection

The inductors should have a saturation (incremental)

current rating equal to or greater than the peak switch-

current limit, which is 1.2A worst-case. However, it’s

generally acceptable to bias the inductor into satura-

tion by 20%, although this will reduce the efficiency.

The 22µH inductor shown in the typical applications cir-

cuit is sufficient for most MAX756/MAX757 application

circuits. Higher input voltages increase the energy

transferred with each cycle, due to the reduced

input/output differential. Minimize excess ripple due to

increased energy transfer by reducing the inductor

value (10µH suggested).

The inductor’s DC resistance significantly affects effi-

ciency. For highest efficiency, limit L1’s DC resistance

to 0.03Ω or less. See Table 1 for a list of suggested

inductor suppliers.

Table 1. Component Suppliers

PRODUCTION

METHOD

Surface-Mount

Miniature

Through-Hole

Low-Cost

Through-Hole

INDUCTORS

Sumida

CD54-220 (22µH)

CoilCraft

DT3316-223

Coiltronics

CTX20-1

Sumida

RCH654-220

CoilCraft

PCH-27-223

CAPACITORS

AVX

TPS series

Sprague

595D series

Sanyo OS-CON

OS-CON series

low-ESR organic

semiconductor

Nichicon

PL series

low-ESR

electrolyic

United Chemi-Con

LXF series

AVX

CoilCraft

Coiltronics

Collmer

Semiconductor

Motorola

Nichicon

Nihon

Sanyo OS-CON

Sprague

Sumida

United

Chemi-Con

USA:

USA:

USA:

(207) 282-5111, FAX (207) 283-1941

(800) 282-9975

(708) 639-6400, FAX (708) 639-1969

(407) 241-7876, FAX (407) 241-9339

USA: (214) 233-1589

USA: (602) 244-3576, FAX (602) 244-4015

USA: (708) 843-7500, FAX (708) 843-2798

Japan: +81-7-5231-8461, FAX (+81-) 7-5256-4158

USA: (805) 867-2555, FAX (805) 867-2556

Japan: +81-3-3494-7411, FAX (+81-) 3-3494-7414

USA: (619) 661-6835

Japan: +81-720-70-1005, FAX (+81-720-) 70-1174

USA: (603) 224-1961, FAX (603) 224-1430

USA: (708) 956-0666

Japan: +81-3-3607-5111, FAX (+81-3-) 3607-5428

USA: (708) 696-2000, FAX (708) 640-6311

Capacitor Selection

A 100µF, 10V surface-mount (SMT) tantalum capacitor

typically provides 50mV output ripple when stepping

up from 2V to 5V at 200mA. Smaller capacitors, down

to 10µF, are acceptable for light loads or in applica-

tions that can tolerate higher output ripple.

6

Maxim Integrated

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