LT1268B/LT1268
7.5A, 150kHz
Switching Regulators
FEATURES
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DESCRIPTIO
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Wide Input Voltage Range: 3.5V to 30V
Low Quiescent Current: 7mA
Internal 7.5A Switch
Very Few External Parts Required
Self-Protected Against Overloads
Available in Standard and Surface Mount
5-Pin Packages
Can Be Externally Synchronized
(See LT1072 Data Sheet)
APPLICATI
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High Efficiency Boost Converter
PC Power Supply with Multiple Outputs
Battery Upconverter
Negative-to-Positive Converter
The LT1268B and LT1268 are monolithic high power
switching regulators. Identical to the popular LT1070,
except for switching frequency (150kHz) and higher
switch current, they can be operated in all standard
switching configurations including buck, boost, flyback,
and inverting. A high current, high efficiency switch is
included on the die along with all oscillator, control, and
protection circuitry. Integration of all functions allows
the LT1268 to be built in standard 5-pin power packages.
This makes it extremely easy to use and provides 鈥渂ust
proof鈥?operations similar to that obtained with 3-pin
linear regulators.
The LT1268 operate with supply voltages from 3.5V to
30V and draw only 7mA quiescent current. By utilizing
current mode switching techniques, it provides excellent
AC and DC load and line regulation.
The LT1268 use an adaptive anti-sat switch drive to allow
very wide ranging load currents with no loss in efficiency.
An externally activated shutdown mode reduces total
supply current to 100碌A typical for standby operation.
USER NOTE:
This data sheet is only intended to provide specifications, graphs, and a general functional
description of the LT1268B/LT1268. Application circuits are included to show the capability of the
LT1268B/LT1268. A complete design manual (AN19) should be obtained to assist in developing new
designs. This manual contains a comprehensive discussion of both the LT1070 and the external
components used with it, as well as complete formulas for calculating the values of these
components. The manual can also be used for the LT1268B/LT1268 factoring in the higher switch
current rating and higher operating frequency.
TYPICAL APPLICATI
V
IN
4.7V TO
5.3V
L1
8碌H, 5A*
D2, D3
鈥?/div>
1N4001
Boost Regulator with 5.3V
鹵1%
Output
D1
MBR1035
L2
2碌H, 5A**
100
V
OUT
5.3V 鹵1%
3.75A
EFFICIENCY (%)
90
V
IN
= 4.7V
+
C3
390碌F
16V
C5
0.02
+
C1
220碌F
16V
V
IN
V
SW
LT1268B FB
R1
4.043k
0.1%
+
C4
390碌F
16V
80
CASE GND
V
C
C2
0.068
R3
220鈩?/div>
R2
1.24k
0.1%
70
60
LT1268 鈥?TA01
*COILTRONICS CTX8-5-52
**COILTRONICS CTX2-5-52
鈥?/div>
OPTIONAL. D2 AND D3 ARE USED TO INCREASE
UNDERVOLTAGE LOCKOUT FROM 2.7V TO
鈮?V.
U
Efficiency of 5.3V Boost Converter
V
IN
= 5.3V
V
IN
= 5V
0
1
2
LOAD CURRENT (A)
LT1268 鈥?TA02
UO
UO
3
4
1
1
2
3
4
