1766 Просмотр технического описания (PDF) - Linear Technology

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1766

5.5V to 60V 1.5A, 200kHz Step-Down Switching Regulator

Linear Technology 

LT1766/LT1766-5

BLOCK DIAGRAM

will have 90° phase shift at a much lower frequency, but

will not have the additional 90° shift until well beyond

the LC resonant frequency. This makes it much easier to

frequency compensate the feedback loop and also gives

much quicker transient response.

Most of the circuitry of the LT1766 operates from an internal

2.9V bias line. The bias regulator normally draws power

from the regulator input pin, but if the BIAS pin is connected

to an external voltage higher than 3V, bias power will be

drawn from the external source (typically the regulated

output voltage). This will improve efficiency if the BIAS

pin voltage is lower than regulator input voltage.

High switch efficiency is attained by using the BOOST

pin to provide a voltage to the switch driver which is

higher than the input voltage, allowing switch to be satu-

rated. This boosted voltage is generated with an external

capacitor and diode. Two comparators are connected to the

shutdown pin. One has a 2.38V threshold for undervoltage

lockout and the second has a 0.4V threshold for complete

shutdown.

VIN 4

BIAS 10

2.9V BIAS

REGULATOR

SYNC 14

SHUTDOWN

COMPARATOR

0.4V

INTERNAL

VCC

SLOPE COMP

ANTISLOPE COMP

RLIMIT

+–

CURRENT

∑

COMPARATOR

200kHz

OSCILLATOR

S

RS

FLIP-FLOP

R

BOOST

6

DRIVER

CIRCUITRY

SHDN 15

5.5μA

+

–

LOCKOUT

COMPARATOR

FREQUENCY

FOLDBACK

VC(MAX)

CLAMP

×1

Q2

FOLDBACK

Q3

CURRENT

LIMIT

CLAMP

ERROR

AMPLIFIER

gm = 2000μMho

RSENSE

Q1

POWER

SWITCH

2 SW

12 FB

11

2.38V

VC

1.22V

GND

1, 8, 9, 16, 17

1766 F01

Figure 1. LT1766 Block Diagram

1766fc

9

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