LINER LT1270CT

LT1270A/LT1270
8A and 10A High Efficiency
Switching Regulators
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DESCRIPTIO
FEATURES
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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
Comes in Standard 5-Pin Package
Can be Externally Synchronized
(See LT1072 Data Sheet)
The LT1270A/LT1270 are monolithic high power switching regulators. Identical to the popular LT1070, except for
switching frequency (60kHz) 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 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.
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APPLICATI
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S
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.
High Efficiency Buck Converter
PC Power Supply with Multiple Outputs
Battery Upconverter
Negative-to-Positive Converter
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 reduces total supply current to 100µA typical for standby
operation.
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.
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TYPICAL APPLICATI
Maximum Output Power*
High Efficiency† Buck Converter
100
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.
BOOST
†
VSW
1N5819
LT1270*
VIN
FB
GND
VC
+
1µF
0.047µF
0.047µF
1k
35µH, 8A*
5V*
5A
ANODE
+
470µF
35V
LT1431CZ REF
CATHODE
MBR1035*
1N4158
560Ω
60
FLYBACK†
40
BUCK-BOOST, VO = 5V
(INVERTING)
20
9.1k
0
0
10k
2N3904
360Ω
BUCK-BOOST,
VO = 12V
(INVERTING)
80
OUTPUT POWER (W)
VIN
(8V TO 25V)
5
15
20
10
INPUT VOLTAGE (V)
25
30
LT1270 • TA02
1000µF
25V
LT1270 • TA01
*MULTIPLY BY 1.2 FOR LT1270A.
BUCK MODE OUTPUT POWER ≈ (7.5A)(VOUT)
†
TRANSFORMER TURNS RATIO MUST BE
OPTIMUM TO ACHIEVE FULL POWER
1
LT1270A/LT1270
PACKAGE/ORDER I FOR ATIO
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W W
W
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
ELECTRICAL CHARACTERISTICS
PARAMETER
CONDITIONS
VREF
Reference Voltage
Measured at Feedback Pin
VC = 0.8V
IB
Feedback Input Current
VFB = VREF
gm
Error Amplifier
Transconductance
∆lC = ±25µA
Error Amplifier Source of
Sink Current
VC = 1.5V
Error Amplifier Clamp Voltage
Hi Clamp, VFB = 1V
Lo Clamp, VFB = 1.5V
Reference Voltage Line Regulation
3V ≤ VIN ≤ VMAX, VC = 0.8V
Error Amplifier Voltage Gain
0.9V ≤ VC ≤ 1.4V
Minimum Input Voltage
IQ
FRONT VIEW
5
4
3
2
1
TJMAX = 100°C, θJA = 2°C/W, θJA = 50°C/ W
●
MIN
TYP
MAX
UNITS
1.224
1.214
1.244
1.244
1.264
1.274
V
V
350
750
1100
nA
nA
3000
2400
4400
●
6000
7000
µmho
µmho
150
120
200
●
350
400
µA
µA
2.30
0.52
V
V
0.03
%/V
1.80
0.25
3V ≤ VIN ≤ VMAX, VC = 0.6V
Control Pin Threshold
Duty Cycle = 0
0.38
●
500
Normal/Flyback Threshold
on Feedback Pin
IFB = 50µA
●
800
2.8
●
Supply Current
Flyback Reference Voltage
mA
7
10
1.08
1.25
V
V
0.40
0.45
0.54
V
15.0
14.0
16.3
17.6
18.0
V
V
4.5
6.8
8.5
V
0.01
0.03
%/V
150
300
650
µmho
70
70
µA
µA
Flyback Reference Voltage
Line Regulation
IFB = 50µA
3V ≤ VIN ≤ VMAX
Flyback Amplifier
Transconductance (gm)
∆lC = ±10µA
Flyback Amplifier Source
and Sink Current
VC = 0.6V Source
IFB = 50µA Sink
●
●
15
25
32
40
BV
Output Switch Breakdown
Voltage
3V ≤ VIN ≤ VMAX
ISW = 5mA
●
60
75
VSAT
Output Switch ON
Resistance (Note 1, 3)
TJ ≤ 100°C
TJ ≤ 125°C
2
V
0.90
0.05 ≤ IFB ≤ 1mA
Control Voltage to Switch
Current Transconductance
V/V
3.0
0.80
0.60
Change in Flyback Reference
Voltage
VFB
LT1270CT
LT1270ACT
T PACKAGE
5-LEAD TO-220
●
VFB
VIN
VSW
GND
FB
VC
ORDER PART
NUMBER
VIN = 15V, VC = 0.5V, VFB = VREF, switch pin open, unless otherwise noted.
SYMBOL
AV
U
RATI GS
W
AXI U
U
ABSOLUTE
0.12
12
V
0.18
0.22
Ω
Ω
A/V
LT1270A/LT1270
ELECTRICAL CHARACTERISTICS
VIN = 15V, VC = 0.5V, VFB = VREF, switch pin open, unless otherwise noted.
SYMBOL
PARAMETER
CONDITIONS
MIN
ILIM
Switch Current Limit (LT1270)
(Note 3)
Duty Cycle = 50%, TJ ≤ 100°C
Duty Cycle = 80%, TJ ≤ 100°C
●
●
8
6
16
14
A
A
ILIM
Switch Current Limit (LT1270A)
(Note 3)
Duty Cycle = 50%, TJ ≤ 100°C
Duty Cycle = 80%, TJ ≤ 100°C
●
●
10.0
7.5
16.0
14.0
A
A
∆IIN
∆ISW
Supply Current Increase
During Switch-ON Time
f
Switching Frequency
●
DCMAX
Maximum Switch Duty Cycle
TYP
MAX
25
40
mA/A
50
50
60
70
70
kHz
kHz
80
92
95
%
100
400
µA
150
250
300
mV
mV
Flyback Sense Delay Time
µs
1.5
Shutdown Mode Supply Current
3V ≤ VIN ≤ VMAX, VC = 0.05V
Shutdown Mode Threshold Voltage
3V ≤ VIN ≤ VMAX
100
50
●
The ● denotes specifications which apply over the full operating
temperature range.
Note 1: Measured with VC in Hi Clamp, VFB = 0.8V.
Note 2: For duty cycles (DC) between 50% and 80%, minimum guaranteed
UNITS
switch current is given by ILIM = 6.67 (1.7 – DC) for the LT1270 and ILIM =
8.33 (1.7 – DC) for the LT1270A.
Note 3: Minimum current limit is reduced by 0.5A at 125°C. 100°C test
limits are guaranteed by correlation to 125°C tests.
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TYPICAL PERFOR A CE CHARACTERISTICS
Switch Saturation Voltage
Switch Current Limit vs Duty Cycle
1.6
2.4
SWITCH SATURATION VOLTAGE (V)
SWITCH CURRENT (A)
TJ = 25°C
1.8
–55°C
25°C
1.2
125°C
6
0
1.2
0.8
0.4
0
0
20
60
40
DUTY CYCLE (%)
80
100
0
2
6
8
4
SWITCH CURRENT (A)
LT1270 • TA03
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.
10
LT1270 • TA04
3
LT1270A/LT1270
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TYPICAL APPLICATIO S
Negative-to-Positive Buck-Boost Converter
Boost Converter (5V to 12V)
5V
L2
55µH*
VIN
OPTIONAL
OUTPUT
FILTER
L1
55µH**
VSW
MBR1020
D1
VIN
12V, 2A
LT1270
VSW
+
10.7k
FB
GND
+ 1000µF
VC
+
25V
1k
1.24k
OPTIONAL
INPUT
FILTER
+
1µF
LT1270
VOUT
12V, 3A
R1
11.3k
C2
2000µF
C4
200µF*
FB
VC
GND
R3
2.2k
C1
0.22µF
L3
PULSE ENGINEERING #PE-92116
C3
LT1270 • TA05
VIN
–12V
1.24k
*REQUIRED IF INPUT LEADS ≥ 2"
**PULSE ENGINEERING #PE-92116
LT1270 • TA06
Negative Buck Converter
+
VIN
+
OPTIONAL
INPUT FILTER
L3
10µH
D1
L1
100µH**
C2
1000µF
–5.2V, 7.5A
VSW
12k
LT1270
C3
100µF*
FB
VC
GND
C1
R2
1.24k
R3
VIN
–20V
OPTIONAL
OUTPUT
FILTER
L2
4µF
LT1270 • TA07
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PACKAGE DESCRIPTIO
0.380 – 0.420
(9.652 – 10.668)
R1
4.64k
LOAD
+ C4
200µF
*REQUIRED IF INPUT LEADS ≥ 2"
**PULSE ENGINEERING #PE-92115
Dimensions in inches (millimeters) unless otherwise noted.
0.079 – 0.135
(2.007 – 3.429)
0.139 – 0.153
(3.531 – 3.886)
DIA
0.560 – 0.650
(14.224 – 16.510)
0.169 – 0.185
(4.293 – 4.699)
0.460 – 0.500
(11.68 – 12.70)
0.866 – 0.913
(21.996 – 23.190)
0.035 – 0.055
(0.889 – 1.397)
0.620 ± 0.020
(15.75 ± 0.508)
0.700 – 0.728
(17.780 – 18.491)
0.970 – 1.050
(24.64 – 26.67)
0.057 – 0.077
(1.448 – 1.956)
4
0.028 – 0.035
(0.711 – 0.889)
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7487
(408) 432-1900 ● FAX: (408) 434-0507 ● TELEX: 499-3977
0.015 – 0.025
(0.381 – 0.635)
0.210 – 0.240
(5.334 – 6.096)
0.327 – 0.335
(8.306 – 8.509)
0.055 – 0.090
(1.397 – 2.286)
0.079 – 0.115
(2.007 – 2.921)
0.170 – 0.185
(4.318 – 4.699)
T5 (FORMED) 0392
LT/GP 1292 5K REV B
 LINEAR TECHNOLOGY CORPORATION 1992