LT1766 Linear Technology, LT1766 Datasheet - Page 7

• Manufacturer Part Number: LT1766
• Description: 5.5V to 60V 1.5A/ 200kHz Step-Down Switching Regulator
• Manufacturer: Linear Technology

BLOCK DIAGRA
The current fed system 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
SHDN
SYNC
BIAS
V
IN
COMPARATOR
10
14
15
4
SHUTDOWN
REGULATOR
+
2.9V BIAS
2.38V
0.4V
–
+
–
W
COMPARATOR
LOCKOUT
5.5 A
INTERNAL
V
CC
ANTISLOPE COMP
SLOPE COMP
OSCILLATOR
200kHz
Figure 1. LT1766 Block Diagram
V
CLAMP
C(MAX)
Q3
+
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 saturated.
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 under-
voltage lockout and the second has a 0.4V threshold for
complete shutdown.
11
V
R
C
1
LIMIT
FOLDBACK
CURRENT
–
CLAMP
LIMIT
CURRENT
COMPARATOR
Q2
S
R
FLIP-FLOP
g
R
m
S
= 2000 Mho
FREQUENCY
FOLDBACK
AMPLIFIER
ERROR
BOOST
LT1766/LT1766-5
CIRCUITRY
6
DRIVER
–
+
1.22V
1766 F01
12
2
Q1
POWER
SWITCH
R
SENSE
FB
GND
1, 8, 9, 16, 17
SW
1766fa
7