LT1270A/LT1270
8A and 10A High Efficiency
Switching Regulators
FEATURES
s
s
s
s
s
s
s
s
DESCRIPTIO
s
Wide Input Voltage Range: 3.5V to 30V
Low Quiescent Current: 7mA
Internal 8A Switch (10A for LT1270A)
Very Few External Parts Required
Self-Protected Against Overloads
Shutdown Mode Draws Only 100µA Supply Current
Flyback-Regulated Mode Has Fully Floating Outputs
Can be Externally Synchronized
(See LT1072 Data Sheet)
Comes in Standard 5-Pin TO-220 Package
APPLICATIO S
s
s
s
s
The LT1270A/LT1270 are monolithic high power switch-
ing regulators. Identical to the popular LT1070, except for
switching frequency (60kHz) and higher switch current,
they can be operated in all standard switching configura-
tions 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. Inte-
gration of all functions allows the LT1270A/LT1270 to be
built in a standard TO-220 power package. This makes it
extremely easy to use and provides “bust proof” operation
similar to that obtained with 3-pin linear regulators.
The LT1270A/LT1270 operate with supply voltages from
3.5V to 30V, and draw only 7mA quiescent current. By
utilizing current-mode switching techniques, they provide
excellent AC and DC load and line regulation.
The LT1270A/LT1270 use adaptive anti-sat switch drive to
allow very wide ranging load currents with no loss in
efficiency. An externally activated shutdown mode re-
duces total supply current to 100µA typical for standby
operation.
High Efficiency Buck Converter
PC Power Supply with Multiple Outputs
Battery Upconverter
Negative-to-Positive Converter
USER NOTE:
This data sheet is only intended to provide specifications, graphs and a general functional
description of the LT1270A/LT1270. Application circuits are included to show the capability of the
LT1270A/LT1270. A complete design manual (AN-19) should be obtained to assist in developing
new designs. AN-19 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. AN-19 can also be used for the LT1270A/LT1270 by factoring in the higher switch
current rating and higher operating frequency.
A comprehensive CAD program called SwitcherCad is also available. Contact the local sales office
in your area or the factory direct.
TYPICAL APPLICATIO
V
IN
(8V TO 25V)
1N5819
V
IN
V
SW
LT1270*
FB
GND
V
C
0.047µF
1k
High Efficiency
†
Buck Converter
100
†
OUTPUT POWER (W)
EFFICIENCY IS
≈
88% @ 2A, 86% @ 5A.
FOR
µPOWER
SHUTDOWN OPTION, CONSULT FACTORY.
*THESE COMPONENTS RATED CONSERVATIVELY TO
IMPROVE EFFICIENCY. MAXIMUM OUTPUT CURRENT
CAN BE 7A. FOR HIGH EFFICIENCY, THE INDUCTOR SHOULD
BE MOLYPERMALLOY OR FERRITE.
+
1µF
0.047µF
35µH, 8A*
5V*
5A
ANODE
9.1k
+
470µF
35V
MBR1035*
2N3904
360Ω
LT1431CZ REF
CATHODE
10k
1N4158
560Ω
1000µF
25V
LT1270 • TA01
U
Maximum Output Power*
BOOST
BUCK-BOOST,
V
O
= 12V
(INVERTING)
FLYBACK
†
80
60
40
20
BUCK-BOOST, V
O
= 5V
(INVERTING)
0
0
5
15
20
10
INPUT VOLTAGE (V)
25
30
LT1270 • TA02
U
U
*MULTIPLY BY 1.2 FOR LT1270A.
BUCK MODE OUTPUT POWER
≈
(7.5A)(V
OUT
)
†
TRANSFORMER TURNS RATIO MUST BE
OPTIMUM TO ACHIEVE FULL POWER
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1
LT1270A/LT1270
ABSOLUTE
(Note 1)
AXI U
RATI GS
PACKAGE/ORDER I FOR ATIO
FRONT VIEW
5
TAB
IS
GND
4
3
2
1
T PACKAGE
5-LEAD PLASTIC TO-220
V
IN
V
SW
GND
FB
V
C
Supply Voltage ....................................................... 30V
Switch Output Voltage ............................................ 60V
Feedback Pin Voltage (Transient, 1ms) ................
±15V
Operating Junction Temperature Range
LT1270AC/LT1270C (Oper.) ................ 0°C to 125°C
LT1270AC/LT1270C (Short-Ckt) ......... 0°C to 140°C
Storage Temperature Range ................ – 65°c to 150°C
Lead Temperature (Soldering, 10 sec)................ 300°C
ORDER PART
NUMBER
LT1270CT
LT1270ACT
T
JMAX
= 100°C,
θ
JA
= 2°C/W,
θ
JA
= 50°C/ W
Consult LTC Marketing for parts specified with wider operating temperature ranges.
ELECTRICAL CHARACTERISTICS
SYMBOL
V
REF
I
B
gm
PARAMETER
Reference Voltage
Feedback Input Current
Error Amplifier
Transconductance
Error Amplifier Source of
Sink Current
Error Amplifier Clamp Voltage
Reference Voltage Line Regulation
Error Amplifier Voltage Gain
Minimum Input Voltage
Supply Current
Control Pin Threshold
Normal/Flyback Threshold
on Feedback Pin
Flyback Reference Voltage
Change in Flyback Reference
Voltage
Flyback Reference Voltage
Line Regulation
Flyback Amplifier
Transconductance (gm)
Flyback Amplifier Source
and Sink Current
Output Switch Breakdown
Voltage
Output Switch ON
Resistance (Note 2, 4)
Control Voltage to Switch
Current Transconductance
Switch Current Limit (LT1270)
(Note 4)
The
q
denotes specifications which apply over the full operating tempera-
ture range, otherwise specifications are at T
A
= 25°C. V
IN
= 15V, V
C
= 0.5V, V
FB
= V
REF
, switch pin open, unless otherwise noted.
CONDITIONS
Measured at Feedback Pin
V
C
= 0.8V
V
FB
= V
REF
∆l
C
=
±25µA
q
q
MIN
1.224
1.214
TYP
1.244
1.244
350
4400
200
V
C
= 1.5V
q
A
V
I
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
3V
≤
V
IN
≤
V
MAX
, V
C
= 0.6V
Duty Cycle = 0
3000
2400
150
120
1.80
0.25
500
0.38
800
2.8
7
0.90
0.45
16.3
6.8
0.01
q
q
MAX
1.264
1.274
750
1100
6000
7000
350
400
2.30
0.52
0.03
3.0
10
1.08
1.25
0.54
17.6
18.0
8.5
0.03
650
70
70
q
0.70
0.50
0.40
15.0
14.0
4.5
UNITS
V
V
nA
nA
µmho
µmho
µA
µA
V
V
%/V
V/V
V
mA
V
V
V
V
V
V
%/V
µmho
µA
µA
V
Ω
Ω
A/V
A
A
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V
FB
V
FB
I
FB
= 50µA
q
0.05
≤
I
FB
≤
1mA
I
FB
= 50µA
3V
≤
V
IN
≤
V
MAX
∆l
C
=
±10µA
V
C
= 0.6V Source
I
FB
= 50µA Sink
3V
≤
V
IN
≤
V
MAX
I
SW
= 1.5mA
T
J
≤
100°C
T
J
≤
125°C
q
q
q
150
15
25
60
300
32
40
75
0.12
12
BV
V
SAT
0.18
0.22
LIM
Duty Cycle = 50%, T
J
≤
100°C
Duty Cycle = 80%, T
J
≤
100°C
q
q
8
6
16
14
2
U
W
U
U
W W
W
LT1270A/LT1270
ELECTRICAL CHARACTERISTICS
SYMBOL
I
LIM
∆I
IN
∆I
SW
f
DC
MAX
PARAMETER
Switch Current Limit (LT1270A)
(Note 4)
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
The
q
denotes specifications which apply over the full operating tempera-
ture range, otherwise specifications are at T
A
= 25°C. V
IN
= 15V, V
C
= 0.5V, V
FB
= V
REF
, switch pin open, unless otherwise noted.
CONDITIONS
Duty Cycle = 50%, T
J
≤
100°C
Duty Cycle = 80%, T
J
≤
100°C
q
q
MIN
10.0
7.5
TYP
MAX
16.0
14.0
40
70
70
95
400
250
300
UNITS
A
A
mA/A
kHz
kHz
%
µs
µA
mV
mV
25
50
50
80
60
92
1.5
100
150
q
3V
≤
V
IN
≤
V
MAX
, V
C
= 0.05V
3V
≤
V
IN
≤
V
MAX
q
100
50
Note 1:
Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
Note 2:
Measured with V
C
in Hi Clamp, V
FB
= 0.8V.
Note 3:
For duty cycles (DC) between 50% and 80%, minimum guaranteed
switch current is given by I
LIM
= 6.67 (1.7 – DC) for the LT1270 and I
LIM
=
8.33 (1.7 – DC) for the LT1270A.
Note 4:
Minimum current limit is reduced by 0.5A at 125°C. 100°C test
limits are guaranteed by correlation to 125°C tests.
TYPICAL PERFOR A CE CHARACTERISTICS
Switch Current Limit vs Duty Cycle
24
SWITCH SATURATION VOLTAGE (V)
1.6
T
J
= 25°C
SWITCH CURRENT (A)
18
25°C
–55°C
12
125°C
6
0
0
20
60
40
DUTY CYCLE (%)
TYPICAL APPLICATIO S
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 representation that the
interconnection of circuits as described herein will not infringe on existing patent rights.
U
U W
Switch Saturation Voltage
1.2
0.8
0.4
80
100
0
0
2
6
8
4
SWITCH CURRENT (A)
10
LT1270 • TA04
LT1270 • TA03
Boost Converter (5V to 12V)
5V
55µH*
V
IN
V
SW
MBR1020
12V, 2A
10.7k
FB
LT1270
GND
V
C
1k
1.24k
+
1000µF
25V
+
1µF
PULSE ENGINEERING #PE-92116
LT1270 • TA05
1270afc
3
LT1270A/LT1270
TYPICAL APPLICATIO S
Negative-to-Positive Buck-Boost Converter
L2
L1
55µH**
D1
V
SW
OPTIONAL
OUTPUT
FILTER
C3
V
IN
+
OPTIONAL
INPUT
FILTER
L3
V
IN
–12V
LT1270
C4
200µF*
FB
GND
V
C
R3
2.2k
C1
0.22µF
LT1270 • TA06
*REQUIRED IF INPUT LEADS
≥
2"
**PULSE ENGINEERING #PE-92116
PACKAGE DESCRIPTIO
.390 – .415
(9.906 – 10.541)
.460 – .500
(11.684 – 12.700)
BSC
.067
(1.70)
.028 – .038
(0.711 – 0.965)
RELATED PARTS
PART NUMBER
LT1074/HV
LTC3414
LT3430/LT3431
DESCRIPTION
4.4A (I
OUT
), 100kHz, High Efficiency Step-Down
DC/DC Converter
4A (I
OUT
), 4MHz, Synchronous Step-Down
DC/DC Converter
60V, 2.75A (I
OUT
), 200/500kHz, High Efficiency
Step-Down DC/DC Converter
COMMENTS
V
IN
: 7.3V to 45/64V, V
OUT
(min) = 2.21V, I
Q
= 8.5mA, I
SD
= 10µA,
DD-5/7, TO220-5/7
V
IN
: 2.3V to 5.5V, V
OUT
(min) = 0.8V, I
Q
= 64µA, I
SD
<1µA,
TSSOP20E
V
IN
: 5.5V to 60V, V
OUT
(min) = 1.2V, I
Q
= 2.5mA, I
SD
= 30µA,
TSSOP16E
1270afc
LT/TP 1203 1K REV C • PRINTED IN USA
4
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900
q
FAX: (408) 434-0507
q
U
U
Negative Buck Converter
+
V
OUT
12V, 3A
V
IN
D1
L1
100µH**
V
SW
C2
1000µF
R1
4.64k
LOAD
–5.2V, 7.5A
12k
+
C2
2000µF
R1
11.3k
+
OPTIONAL
INPUT FILTER
L3
10µH
LT1270
C3
100µF*
FB
GND
V
C
C1
R3
R2
1.24k
OPTIONAL
OUTPUT
FILTER
L2
4µF
1.24k
+
C4
200µF
V
IN
–20V
LT1270 • TA07
*REQUIRED IF INPUT LEADS
≥
2"
**PULSE ENGINEERING #PE-92115
T Package
5-Lead Plastic TO-220 (Standard)
(Reference LTC DWG # 05-08-1421)
.147 – .155
(3.734 – 3.937)
DIA
.230 – .270
(5.842 – 6.858)
.570 – .620
(14.478 – 15.748)
.330 – .370
(8.382 – 9.398)
.700 – .728
(17.78 – 18.491)
.620
(15.75)
TYP
.165 – .180
(4.191 – 4.572)
.045 – .055
(1.143 – 1.397)
SEATING PLANE
.152 – .202
.260 – .320 (3.861 – 5.131)
(6.60 – 8.13)
.095 – .115
(2.413 – 2.921)
.155 – .195*
(3.937 – 4.953)
.013 – .023
(0.330 – 0.584)
.135 – .165
(3.429 – 4.191)
* MEASURED AT THE SEATING PLANE
T5 (TO-220) 0801
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