LT1766_1 datasheet(9/30 Pages) LINER

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LT1766/LT1766-5

1766fc

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

–

∑

VIN

2.9V BIAS

REGULATOR

200kHz

OSCILLATOR

FREQUENCY

FOLDBACK

GND

1, 8, 9, 16, 17

1766 F01

SLOPE COMP

ANTISLOPE COMP

BIAS

INTERNAL

VCC

SYNC

0.4V

5.5μA

CURRENT

COMPARATOR

RLIMIT

RSENSE

ERROR

AMPLIFIER

gm = 2000μMho

FOLDBACK

CURRENT

LIMIT

CLAMP

BOOST

FLIP-FLOP

DRIVER

CIRCUITRY

POWER

SWITCH

1.22V

SHDN 15

LOCKOUT

COMPARATOR

SHUTDOWN

COMPARATOR

2.38V

×1

VC(MAX)

CLAMP

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.

Figure 1. LT1766 Block Diagram

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