LT1271/LT1269
4A High Efficiency
Switching Regulators
FEATURES
s
s
s
s
s
s
s
s
s
DESCRIPTIO
Wide Input Voltage Range 3.5V to 30V
Low Quiescent Current: 7mA
Internal 4A Switch
Very Few External Parts Required
Self Protected Against Overloads
Shutdown Mode Draws Only 100µA Supply Current
Flyback Regulated Mode Has Fully Floating Outputs
Comes in Standard 5-Pin Package
Can Be Externally Synchronized (See LT1072 Data Sheet)
APPLICATI
s
s
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s
s
S
Boost Converter
High Efficiency Buck Converter
PC Power Supply with Multiple Outputs
Battery Up-Converter
Negative-to-Positive Converter
The LT
®
1271 and LT1269 are monolithic high power
switching regulators. Identical to the popular LT1070,
except for switching frequency (LT1271 = 60kHz, LT1269
= 100kHz) and slightly lower switch current, they can be
operated in all standard switching configurations includ-
ing 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 LT1271/LT1269 to be built in a
standard TO-220 power package. This makes them ex-
tremely easy to use and provides “bust proof” operation
similar to that obtained with 3-pin linear regulators.
The LT1271/LT1269 operate with supply voltages from
3.5V to 30V, and draw only 7mA quiescent current. By
utilizing current mode switching techniques, they pro-
vides excellent AC and DC load and line regulation.
A patented adaptive antisat switch drive allows very wide
ranging load currents with no loss in efficiency. An exter-
nally activated shutdown mode reduces total supply cur-
rent to 100µA typical for standby operation.
, LTC and LT are registered trademarks of Linear Technology Corporation.
Burst Mode is a trademark of Linear Technology Corporation.
USER NOTE:
This data sheet is only intended to provide specifications, graphs, and a general functional
description of the LT1271/LT1269. Application circuits are included to show the capability of the
LT1271/LT1269. A complete design manual (AN-19) 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 LT1271/LT1269 by factoring in the higher switch
current rating and higher operating frequency.
TYPICAL APPLICATION
High Efficiency 5V Regulator with Burst Mode
TM
Operation
50
V
IN
6.5V TO 25V
V
SW
LT1271
FB
V
C
0.02µF
680Ω
0.1µF
0.03µF 4.7µF
TANT
GND
1N4148
V
IN
OUTPUT POWER (W)
EFFICIENCY
≈
90%
AT I
OUT
= 0.4A TO 1.5A
+
L1
25µH
TO 50µH
0.015Ω
MBR
330pF
V
+
V
LIM
LT1432
V
OUT
MODE
GND
+
V
OUT
5V, 3A
390µF
16V
V
C
C1
200µF
35V
DIODE
+
V
IN
< 0.3V = NORMAL RUN MODE
> 2.5V = SHUTDOWN
OPEN = BURST MODE OPERATION
127/691 TA01
U
Maximum Output Power
40
BOOST
BUCK-BOOST
V
O
= 12V
(INVERTING)
30
FLYBACK
†
20
BUCK-BOOST
V
O
= 5V
(INVERTING)
0
5
15
20
10
INPUT VOLTAGE (V)
25
30
10
0
1271/69 TA02
U
UO
BUCK MODE OUTPUT POWER
≈
(3.5A)(V
OUT
)
†
TRANSFORMER TURNS RATIO MUST BE
OPTIMUM TO ACHIEVE FULL POWER.
1
LT1271/LT1269
ABSOLUTE
AXI U
RATI GS
Operating Junction Temperature Range
Operating .............................................. 0°C to 100°C
Short Circuit ......................................... 0°C to 125°C
Lead Temperature (Soldering, 10 sec.)................ 300°C
Supply Voltage ....................................................... 30V
Switch Output Voltage ............................................ 60V
Feedback Pin Voltage (Transient, 1ms) ................
±15V
Storage Temperature Range ................ – 65°C to 150°C
PACKAGE/ORDER I FOR ATIO
FRONT VIEW
5
4
3
2
1
V
IN
V
SW
GND
FB
V
C
ORDER PART
NUMBER
V
SW
1
LT1271CQ
LT1269CQ
POWER
SWITCH
Q PACKAGE
5-LEAD PLASTIC DD
T
J MAX
= 100°C,
θ
JC
= 4°C/W,
θ
JA
= 30°C/W*
FRONT VIEW
5
4
3
2
1
T PACKAGE
5-LEAD PLASTIC TO-220
T
J MAX
= 100°C,
θ
JC
= 4°C/W,
θ
JA
= 50°C/W
*With device soldered to 1/2 square inch of 1oz copper over backside or internal layer
ground plane. Consult factory for Industrial and Military grade parts.
V
IN
V
SW
GND
FB
V
C
ORDER PART
NUMBER
LT1271CT
LT1269CT
ELECTRICAL CHARACTERISTICS
SYMBOL
V
REF
I
B
gm
PARAMETER
Reference Voltage
Feedback Input Current
Error Amplifier
Transconductance
Error Amplifier Source or
Sink Current
Error Amplifier Clamp
Voltage
Reference Voltage Line
Regulation
A
V
I
Q
Error Amplifier Voltage Gain
Minimum Input Voltage (Note 3)
Supply Current
V
IN
= 15V, V
C
= 0.5V, V
FB
= V
REF,
switch pin open, unless otherwise noted.
MIN
q
q
CONDITIONS
Measured at Feedback Pin
V
C
= 0.8V
V
FB
= V
REF
∆I
C
=
±25µA
q
V
C
= 1.5V
q
Hi Clamp, V
FB
= 1V
Lo Clamp, V
FB
= 1.5V
3V
≤
V
IN
≤
V
MAX,
V
C
= 0.8V
0.9V
≤
V
C
≤
1.4V
q
q
3V
≤
V
IN
≤
V
MAX
, V
C
= 0.6V
2
U
U
W
W W
U
W
TOP VIEW
20 V
SW
19 V
SW
18 NC
17 GND
16 GND
15 GND
14 GND
13 V
IN
12 NC
11 NC
POWER
SWITCH
ORDER PART
NUMBER
LT1269CS
V
SW
2
NC 3
GND 4
GND 5
GND 6
GND 7
AGND 8
V
C
9
FB 10
SW PACKAGE
20-LEAD PLASTIC WIDE SO
θ
WILL VARY FROM APPROXIMATELY 40°C/W
WITH 0.75 SQ. IN. OF 1 OZ. COPPER TO 46°C/W
WITH 0.33 SQ. IN. OF 1 OZ. COPPER
TYP
1.244
1.244
350
MAX
1.264
1.274
750
1100
6000
7000
350
400
2.3
0.52
0.03
UNITS
V
V
nA
nA
µmho
µmho
µA
µA
V
V
%/V
V/V
1.224
1.214
3000
2400
150
120
1.8
0.25
4400
200
0.38
500
800
2.8
7
3.0
10
V
mA
LT1271/LT1269
ELECTRICAL CHARACTERISTICS
SYMBOL
PARAMETER
Control Pin Threshold
Normal/Flyback Threshold
on Feedback Pin
V
FB
V
FB
Flyback Reference Voltage
Change in Flyback
Reference Voltage
Flyback Reference Voltage
Line Regulation
Flyback Amplifier
Transconductance (gm)
Flyback Amplifier Source
and Sink Current
BV
V
SAT
Output Switch Breakdown
Voltage
Output Switch (Note 1)
“On” Resistance
Control Voltage to Switch
Current Transconductance
I
LIM
∆I
IN
∆I
SW
f
DC (max)
Switch Current Limit (Note 2)
Supply Current Increase
During Switch On-Time
Switching Frequency
Maximum Switch Duty Cycle
Flyback Sense Delay Time
Shutdown Mode
Supply Current
Shutdown Mode
Threshold Voltage
3V
≤
V
IN
≤
V
MAX
, V
C
= 0.05V
3V
≤
V
IN
≤
V
MAX
q
V
IN
= 15V, V
C
= 0.5V, V
FB
= V
REF,
switch pin open, unless otherwise noted.
MIN
q
CONDITIONS
Duty Cycle = 0
TYP
0.9
0.45
16.3
6.8
0.01
MAX
1.08
1.25
0.54
17.6
18
8.5
0.03
650
70
70
UNITS
V
V
V
V
V
V
%/V
µmho
µA
µA
V
0.7
0.5
0.4
I
FB
= 50µA
q
15
14
4.5
0.05
≤
I
FB
≤
1mA
I
FB
= 50µA
3V
≤
V
IN
≤
V
MAX
∆I
C
=
±10µA
V
C
= 0.6V
I
FB
= 50µA
3V
≤
V
IN
≤
V
MAX
I
SW
= 1.5mA
Source
Sink
q
q
q
q
150
15
25
60
300
32
40
75
0.2
6.4
0.33
Ω
A/V
Duty Cycle = 50%
Duty Cycle = 80%
q
q
4
3.2
25
8
8
40
70
115
95
95
400
250
300
A
A
mA/A
kHz
kHz
%
%
µs
µA
mV
mV
LT1271
LT1269
LT1271
LT1269
q
q
50
85
85
80
60
100
92
90
1.5
100
100
50
150
The
q
denotes the specifications which apply over the full operating
temperature range.
Note 1:
Measured with V
C
in hi clamp, V
FB
= 0.8V.
Note 2:
For duty cycles (DC) between 50% and 85%, minimum
guaranteed switch current is given by I
LIM
= 2.67 (2 – DC).
Note 3:
Minimum input voltage.
3
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