LT1302 Ver la hoja de datos (PDF) - Linear Technology

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componentes Descripción

Fabricante

LT1302

Micropower High Output Current Step-Up Adjustable and Fixed 5V DC/DC Converters

Linear Technology 

LT1302/LT1302-5

APPLICATIONS INFORMATION

and there is no low frequency component. The total ESR

is under 0.03Ω. If a single 100µF aluminum electrolytic

capacitor is used instead, the converter mode-hops be-

tween current mode and Burst Mode due to high ESR,

causing the voltage comparator to trip as shown in Figure

5. The ripple voltage is now over 500mVP-P and contains

a low frequency component. Maximum allowable output

capacitor ESR can be calculated by the following formula:

ESRMAX

=

VOS × VOUT

VREF × 1A

where,

VOS = 15mV

VREF = 1.24V

Input Capacitor

The input supply should be decoupled with a good quality

electrolytic capacitor close to the LT1302 to provide a

stable input supply. Long leads or traces from power

source to the switcher can have considerable impedance

at the LT1302’s switching frequency. The input capacitor

provides a low impedance at high frequency. A 0.1µF

ceramic capacitor is required right at the VIN pin. When the

input voltage can be above 5V, a 10Ω/1µF decoupling

network for VIN is recommended as detailed in Figure 6.

This network is also recommended when driving a trans-

former.

VIN > 5V

10Ω

VOUT

50mV/DIV

AC COUPLED

ILOAD

510mA

10mA

500µs/DIV

1302 F04

Figure 4. Low ESR Output Capacitor Results in Stable

Operation. Ripple Voltage is Under 30mVP-P

VOUT

200mV/DIV

AC COUPLED

510mA

ILOAD 10mA

500µs/DIV

1302 F05

Figure 5. Inexpensive Electrolytic Capacitor Has High

ESR, Resulting in Mode-Hop, Ripple Voltage Amplitude Is

Over 500mVP-P and Includes Low Frequency Component

VIN

SW

+ 47µF +

TO

1µF

100µF

LT1302

•••

GND PGND

1302 F06

Figure 6. A 10Ω/1µF Decoupling Network at VIN Is

Recommended When Input Voltage Is Above 5V

Table 2 lists capacitor vendors along with device types.

Table 2. Recommended Capacitors

VENDOR

AVX

Sanyo

Sprague

SERIES

TPS

OS-CON

595D

TYPE

Surface Mount

Through Hole

Surface Mount

PHONE NO.

(803) 448-9411

(619) 661-6835

(603) 224-1961

Diode Selection

A 2A Schottky diode such as Motorola MBRS130LT3 has

been found to be the best available. Other choices include

1N5821 or MBRS130T3. Do not use “general purpose”

diodes such as 1N4001. They are much too slow for use

in switching regulator applications.

8

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