Datasheet

7
LT1507
BLOCK DIAGRAM
W
APPLICATIONS INFORMATION
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FEEDBACK PIN FUNCTIONS
The feedback pin (FB or SENSE) on the LT1507 is used to
set output voltage and also to 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
Note: This application section is adapted from the more
complete version found in the LT1375/LT1376 data sheet.
If more details are desired consult the LT1375/LT1376
Applications Information section, but please acquaint
yourself thoroughly with this LT1507 information first so
that differences between the LT1375 and the LT1507 do
not cause confusion.
Figure 1. Block Diagram
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Σ
V
IN
2.9V BIAS
REGULATOR
500kHz
OSCILLATOR
FREQUENCY
SHIFT CIRCUIT
V
SW
FB/SENSE
7
3
1
8
4
5
2
6
V
C
GND
LT1507 • BD
SLOPE COMP
0.1Ω
BIAS
INTERNAL
V
CC
CURRENT
SENSE
AMPLIFIER
VOLTAGE GAIN = 5
SYNC
SHUTDOWN
COMPARATOR
CURRENT
COMPARATOR
ERROR
AMPLIFIER
g
m
= 2000µmho
FOLDBACK
CURRENT
LIMIT
CLAMP
BOOST
R
S

FLIP-FLOP
DRIVER
CIRCUITRY
S
R

0.9V
SHDN
LOCKOUT
COMPARATOR
0.4V
3.5µA
Q2
Q1
POWER
SWITCH
2.38V
2.42V
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