MAX1760 Просмотр технического описания (PDF) - Maxim Integrated

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MAX1760

0.8A, Low-Noise, 1MHz, Step-Up DC-DC Converter

Maxim Integrated 

0.8A, Low-Noise, 1MHz,

Step-Up DC-DC Converter

Table 3. Component Selection Guide

PRODUCTION METHOD

INDUCTORS

TOKO type D52LC

Surface mount

TOKO type D518LC

Sumida CDRH5D18

Sumida CDRH4D28

CAPACITORS

AVX TPS series

Kemet T510 series

Sanyo POSCAP series

—

DIODES

EIC SB series

Motorola MBR0520L

—

—

Table 4. Component Suppliers

SUPPLIER

PHONE

AVX

EIC

Kemet

USA: 843-448-9411

USA: 916-941-0712

USA: 810-287-2536

Motorola

USA: 408-629-4789

Japan: 81-45-474-7030

Sumida

USA: 847-956-0666

Japan: 011-81-3-3667-3302

TOKO

USA: 847-297-0070

Note: Please indicate that you are using the MAX1760 when

contacting these component suppliers.

time constant is:

tSS = RSSCSS

where RSS ≥ 470kΩ.

Placing a capacitor across the lower resistor of the cur-

rent-limiting resistive divider provides both current-limit

and soft-start features simultaneously (Figures 4 and 5).

Inductor Selection

The MAX1760’s high switching frequency allows the

use of a small 3.3µH surface-mount inductor. The cho-

sen inductor should generally have a saturation current

rating exceeding the N-channel switch current limit;

however, it is acceptable to bias the inductor current

into saturation by as much as 20% if a slight reduction

in efficiency is acceptable. Lower current-rated induc-

tors may be used if ISET is employed to reduce the

peak inductor current (see the Setting the Switch

Current Limit and Soft-Start section). For high efficien-

cy, choose an inductor with a high-frequency ferrite

core material to reduce core losses. To minimize radiat-

ed noise, use a toroid or shielded inductor. See Table 3

for suggested components and Table 4 for a list of

component suppliers. Connect the inductor from the

battery to the LX pin as close to the IC as possible.

External Diode

For output voltages greater than 4V, an external

Schottky diode must be connected from LX to POUT, in

parallel with the on-chip synchronous rectifier (Figure

6). The diode should be rated for 0.5A. Representative

devices are Motorola MBR0520L, Nihon EP05Q03L, or

generic 1N5817. This external diode is also recom-

mended for applications that must start with input volt-

ages at or below 1.8V. The Schottky diode carries

current during startup and after the synchronous rectifi-

er turns off; thus, its current rating only needs to be

500mA. Connect the diode as close to the IC as possi-

ble. Do not use ordinary rectifier diodes; their slow

switching speeds and long reverse-recovery times ren-

der them unacceptable. For circuits that do not require

startup with inputs below 1.8V and have an output of 4V

or less, no external diode is needed.

Input and Output Filter Capacitors

Choose input and output filter capacitors that will ser-

vice the input and output peak currents with accept-

able voltage ripple. Choose input capacitors with

working voltage ratings over the maximum input volt-

VIN = 0.7V

TO VOUT

3.3µH

33µF

0.22µF

CLK/SEL

ON

LX

MAX1760

POUT

ISET

REF

OUT

PGND GND FB

MRB0520L

4.7Ω

0.68µF

VOUT

100µF

Figure 6. Connection with External Schottky Diode for Output

Voltages Greater than 4V, or to Assist Low-Voltage Startup

10 ______________________________________________________________________________________

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