LT1576CS8 datasheet(8/28 Pages) LINER

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LT1576/LT1576-5

APPLICATIONS INFORMATION

–

INPUT

2.9V BIAS

REGULATOR

200kHz

OSCILLATOR

FREQUENCY

SHIFT CIRCUIT

VSW

LOCKOUT

COMPARATOR

GND

1576 BD

SLOPE COMP

0.025

Ω

BIAS

INTERNAL

VCC

CURRENT

SENSE

AMPLIFIER

VOLTAGE GAIN = 35

SYNC

SHDN

SHUTDOWN

COMPARATOR

CURRENT

COMPARATOR

ERROR

AMPLIFIER

gm = 1000µMho

FOLDBACK

CURRENT

LIMIT

CLAMP

BOOST

FLIP-FLOP

DRIVER

CIRCUITRY

0.8V

POWER

SWITCH

1.21V

2.44V

–

0.4V

3.5

µA

Figure 1. Block Diagram

BLOCK DIAGRAM

FEEDBACK PIN FUNCTIONS

The feedback (FB) pin on the LT1576 is used to set output

voltage and provide several overload protection features.

The first part of this section deals with selecting resistors

to set output voltage and the remaining part talks about

foldback frequency and current limiting created by the FB

pin. Please read both parts before committing to a final

design. The fixed 5V LT1576-5 has internal divider resis-

tors and the FB pin is renamed SENSE, connected directly

to the output.

The suggested value for the output divider resistor (see

Figure 2) from FB to ground (R2) is 5k or less, and a

formula for R1 is shown below. The output voltage error

caused by ignoring the input bias current on the FB pin is

less than 0.25% with R2 = 5k. A table of standard 1%

values is shown in Table 1 for common output voltages.

Please read the following if divider resistors are increased

above the suggested values.

RVOUT

21 21

121

−

()

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