1
LT1271/LT1269
4A High Efficiency
Switching Regulators
TYPICAL APPLICATION
U
D
U
ESCRIPTIO
S
FEATURE
■
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)
U
S
A
O
PPLICATI
■
Boost Converter
■
High Efficiency Buck Converter
■
PC Power Supply with Multiple Outputs
■
Battery Up-Converter
■
Negative-to-Positive Converter
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.
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.
INPUT VOLTAGE (V)
0
0
OUTPUT POWER (W)
10
20
30
510 15 20
1271/69 TA02
25
40
50
30
BOOST
BUCK-BOOST
V
O
= 5V
(INVERTING)
FLYBACK
†
BUCK-BOOST
V
O
= 12V
(INVERTING)
BUCK MODE OUTPUT POWER
≈
(3.5A)(V
OUT
)
TRANSFORMER TURNS RATIO MUST BE
OPTIMUM TO ACHIEVE FULL POWER.
†
Maximum Output Power
V
SW
FB
GND
V
IN
V
C
LT1271
C1
200µF
35V
0.02µF
0.1µF
680Ω0.03µF
4.7µF
TANT
1N4148
L1
25µH
TO 50µH0.015Ω
390µF
16V
V
OUT
5V, 3A
<0.3V = NORMAL RUN MODE
>2.5V = SHUTDOWN
OPEN = BURST MODE OPERATION
V
IN
6.5V TO 25V
127/691 TA01
V
C
V
IN
MODE
V
OUT
V
LIM
V
+
LT1432
GND
DIODE
MBR
330pF
EFFICIENCY
≈
90%
AT I
OUT
= 0.4A TO 1.5A
+
+
+
High Efficiency 5V Regulator with Burst Mode
TM
Operation
2
LT1271/LT1269
A
U
G
W
A
W
U
W
ARBSOLUTEXI T
I
S
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
WU
U
PACKAGE/ORDER I FOR ATIO
ORDER PART
NUMBER
V
IN
V
SW
GND
FB
V
C
T PACKAGE
5-LEAD PLASTIC TO-220
FRONT VIEW
5
4
3
2
1
T
J MAX
= 100°C, θ
JC
= 4°C/W, θ
JA
= 50°C/W
Q PACKAGE
5-LEAD PLASTIC DD
FRONT VIEW
V
IN
V
SW
GND
FB
V
C
5
4
3
2
1
T
J MAX
= 100°C, θ
JC
= 4°C/W, θ
JA
= 30°C/W*
LT1271CQ
LT1269CQ
ORDER PART
NUMBER
LT1271CT
LT1269CT
ORDER PART
NUMBER
LT1269CS
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
1
2
3
4
5
6
7
8
9
10
TOP VIEW
SW PACKAGE
20-LEAD PLASTIC WIDE SO
20
19
18
17
16
15
14
13
12
11
VSW
VSW
NC
GND
GND
GND
GND
AGND
VC
FB
VSW
VSW
NC
GND
GND
GND
GND
VIN
NC
NC
POWER
SWITCH POWER
SWITCH
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
V
REF
Reference Voltage Measured at Feedback Pin 1.224 1.244 1.264 V
V
C
= 0.8V ●1.214 1.244 1.274 V
I
B
Feedback Input Current V
FB
= V
REF
350 750 nA
●1100 nA
gm Error Amplifier ∆I
C
= ±25µA 3000 4400 6000 µmho
Transconductance ●2400 7000 µmho
Error Amplifier Source or V
C
= 1.5V 150 200 350 µA
Sink Current ●120 400 µA
Error Amplifier Clamp Hi Clamp, V
FB
= 1V 1.8 2.3 V
Voltage Lo Clamp, V
FB
= 1.5V 0.25 0.38 0.52 V
Reference Voltage Line 3V ≤ V
IN
≤ V
MAX,
V
C
= 0.8V ●0.03 %/V
Regulation
A
V
Error Amplifier Voltage Gain 0.9V ≤ V
C
≤ 1.4V 500 800 V/V
Minimum Input Voltage (Note 3) ●2.8 3.0 V
I
Q
Supply Current 3V ≤ V
IN
≤ V
MAX
, V
C
= 0.6V 7 10 mA
VIN = 15V, VC = 0.5V, VFB = VREF, switch pin open, unless otherwise noted.
ELECTRICAL C CHARA TERISTICS
*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.
3
LT1271/LT1269
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
Control Pin Threshold Duty Cycle = 0 0.7 0.9 1.08 V
●0.5 1.25 V
Normal/Flyback Threshold 0.4 0.45 0.54 V
on Feedback Pin
V
FB
Flyback Reference Voltage I
FB
= 50µA 15 16.3 17.6 V
●14 18 V
V
FB
Change in Flyback 0.05 ≤ I
FB
≤ 1mA 4.5 6.8 8.5 V
Reference Voltage
Flyback Reference Voltage I
FB
= 50µA 0.01 0.03 %/V
Line Regulation 3V ≤ V
IN
≤ V
MAX
Flyback Amplifier ∆I
C
= ±10µA 150 300 650 µmho
Transconductance (gm)
Flyback Amplifier Source V
C
= 0.6V Source ●15 32 70 µA
and Sink Current I
FB
= 50µA Sink ●25 40 70 µA
BV Output Switch Breakdown 3V ≤ V
IN
≤ V
MAX
●60 75 V
Voltage I
SW
= 1.5mA
V
SAT
Output Switch (Note 1) ●0.2 0.33 Ω
“On” Resistance
Control Voltage to Switch 6.4 A/V
Current Transconductance
I
LIM
Switch Current Limit (Note 2) Duty Cycle = 50% ●48A
Duty Cycle = 80% ●3.2 8 A
∆I
IN
Supply Current Increase 25 40 mA/A
∆I
SW
During Switch On-Time
f Switching Frequency LT1271 ●50 60 70 kHz
LT1269 ●85 100 115 kHz
DC (max) Maximum Switch Duty Cycle LT1271 85 92 95 %
LT1269 80 90 95 %
Flyback Sense Delay Time 1.5 µs
Shutdown Mode 3V ≤ V
IN
≤ V
MAX
, V
C
= 0.05V 100 400 µA
Supply Current
Shutdown Mode 3V ≤ V
IN
≤ V
MAX
100 150 250 mV
Threshold Voltage ●50 300 mV
ELECTRICAL C CHARA TERISTICS
VIN = 15V, VC = 0.5V, VFB = VREF, switch pin open, unless otherwise noted.
The ● 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.
4
LT1271/LT1269
CCHARA TERISTICS
UW
AT
Y
P
I
CALPER
F
O
RC
E
Switch Current Limit vs Duty Cycle Switch Saturation Voltage
DUTY CYCLE (%)
0
SWITCH CURRENT (A)
9
12
40
1271/69 G01
6
3
010 20 30 50 60 70 80 90 100
–55°C
125°C
25°C
SWITCH CURRENT (A)
0
0.4
SWITCH SATURATION VOLTAGE (V)
0.6
0.8
1.0
1.2
1.4
1.6
1234
1271/69 G02
5
0.2
0
TJ = 25°C
U
SA
O
PPLICATITYPICAL
C1
0.22µF
L1**
100µH
D1
MBR340
1271/69 TA04
LT1271
VSW
FB
GND
VIN
VC
C2
200µF
* REQUIRED IF INPUT LEADS ≥ 2"
** COILTRONICS CTX100-2-52
×
×R1
11.3k
Q1
2N3906
OPTIONAL
OUTPUT
FILTER
L2
C3
R3
2.2k
VIN
–12V
VOUT
12V, 1.5A
C4*
200µF
OPTIONAL
INTPUT
FILTER
L3
R2
1.24k
+
+
Negative-to-Positive Buck-Boost Converter
5
LT1271/LT1269
U
SA
O
PPLICATITYPICAL
Boost Converter (5V to 12V)
1µF
100µH*
MBR330
10.7k
1271/69 TA03
5V
12V
0.5A
LT1271
VSW
FB
GND
VIN
VC
1.24k
100µF
25V
1k
* COILTRONICS CTX100-2-52
+
U
PACKAGE DESCRIPTIO
Dimensions in inches (millimeters) unless otherwise noted.
Q Package
5-Lead Plastic DD Pak
(LTC DWG # 05-08-1461)
Q(DD5) 0396
0.028 – 0.038
(0.711 – 0.965)
0.143+0.012
–0.020
()
3.632+0.305
–0.508
0.057 – 0.077
(1.447 – 1.955) 0.013 – 0.023
(0.330 – 0.584)
0.095 – 0.115
(2.413 – 2.921)
0.004+0.008
–0.004
()
0.102+0.203
–0.102
0.050 ± 0.012
(1.270 ± 0.305)
0.059
(1.499)
TYP
0.045 – 0.055
(1.143 – 1.397)
0.165 – 0.180
(4.191 – 4.572)
0.330 – 0.370
(8.382 – 9.398)
0.060
(1.524)
TYP
0.390 – 0.415
(9.906 – 10.541)
15° TYP
0.300
(7.620)
0.075
(1.905)
0.183
(4.648)
0.060
(1.524)
0.060
(1.524)
0.256
(6.502)
BOTTOM VIEW OF DD PAK
HATCHED AREA IS SOLDER PLATED
COPPER HEAT SINK
6
LT1271/LT1269
U
PACKAGE DESCRIPTIO
Dimensions in inches (millimeters) unless otherwise noted.
T Package
5-Lead Plastic TO-220 (Standard)
(LTC DWG # 05-08-1421)
T5 (TO-220) 0398
0.028 – 0.038
(0.711 – 0.965)
0.057 – 0.077
(1.448 – 1.956) 0.135 – 0.165
(3.429 – 4.191)
0.700 – 0.728
(17.78 – 18.491)
0.045 – 0.055
(1.143 – 1.397)
0.095 – 0.115
(2.413 – 2.921)
0.013 – 0.023
(0.330 – 0.584)
0.620
(15.75)
TYP
0.155 – 0.195
(3.937 – 4.953)
0.152 – 0.202
(3.861 – 5.131)
0.260 – 0.320
(6.60 – 8.13)
0.165 – 0.180
(4.191 – 4.572)
0.147 – 0.155
(3.734 – 3.937)
DIA
0.390 – 0.415
(9.906 – 10.541)
0.330 – 0.370
(8.382 – 9.398)
0.460 – 0.500
(11.684 – 12.700)
0.570 – 0.620
(14.478 – 15.748)
0.230 – 0.270
(5.842 – 6.858)
7
LT1271/LT1269
U
PACKAGE DESCRIPTIO
Dimensions in inches (millimeters) unless otherwise noted.
SW Package
20-Lead Plastic Small Outline (Wide 0.300)
(LTC DWG # 05-08-1620)
S20 (WIDE) 0396
NOTE 1
0.496 – 0.512*
(12.598 – 13.005)
20 19 18 17 16 15 14 13
12345678
0.394 – 0.419
(10.007 – 10.643)
910
1112
0.037 – 0.045
(0.940 – 1.143)
0.004 – 0.012
(0.102 – 0.305)
0.093 – 0.104
(2.362 – 2.642)
0.050
(1.270)
TYP 0.014 – 0.019
(0.356 – 0.482)
TYP
0° – 8° TYP
NOTE 1
0.009 – 0.013
(0.229 – 0.330) 0.016 – 0.050
(0.406 – 1.270)
0.291 – 0.299**
(7.391 – 7.595)
× 45°
0.010 – 0.029
(0.254 – 0.737)
NOTE:
1. PIN 1 IDENT, NOTCH ON TOP AND CAVITIES ON THE BOTTOM OF PACKAGES ARE THE MANUFACTURING OPTIONS.
THE PART MAY BE SUPPLIED WITH OR WITHOUT ANY OF THE OPTIONS
DIMENSION DOES NOT INCLUDE MOLD FLASH. MOLD FLASH SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE
DIMENSION DOES NOT INCLUDE INTERLEAD FLASH. INTERLEAD FLASH SHALL NOT EXCEED 0.010" (0.254mm) PER SIDE
*
**
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no represen-
tation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
8
LT1271/LT1269
LINEAR TECHNOLOGY CORPORATION 1992
TYPICAL APPLICATION
U
Negative Buck Converter
C1
L1**
100µH
D1
MBR735
1271/69 TA05
12k
LT1271
V
SW
FB
GND
V
IN
V
C
C2
100µF
* REQUIRED IF INPUT LEADS ≥ 2"
** COILTRONICS CTX100-2-52
×
×
R1
4.64k
Q1
2N3906
R3
V
IN
–8V TO –30V
C3*
100µF
OPTIONAL
INTPUT
FILTER
L3
10µHR2
1.24k
LOAD
OPTIONAL
OUTPUT
FILTER
L2
4µH
C4
200µF
–5.2V AT 3.5A
+
+
+
127169fb LT/TP 0798 2K REV B • PRINTED IN USA
RELATED PARTS
PART NUMBER DESCRIPTION COMMENTS
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IN
Up to 40V
LT1370 500kHz, 6A Boost Switching Regulator 6A, 42V Internal Switch
LT1371 500kHz, 3A Boost Switching Regulator 3A, 42V Internal Switch, 90% Efficiency
LT1372 500kHz, 1.5A Boost Switching Regulator Also Regulates Negative Flyback Outputs
LT1374 500kHz, 4.5A Buck Switching Regulator V
IN
Up to 25V, SO-8 Package
LT1376 500kHz, 1.5A Buck Switching Regulator V
IN
Up to 25V, Uses 4.7µH Inductor
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900
●
FAX: (408) 434-0507
●
www.linear-tech.com
