LT1270C [Linear]
8A and 10A High Efficiency Switching Regulators; 8A和10A高效率开关稳压器
| 型号： | LT1270C |
| 厂家： | 
Linear |
| 描述： | 8A and 10A High Efficiency Switching Regulators |
| 文件： | 总4页 (文件大小：182K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
LT1270A/LT1270
8A and 10A High Efficiency
Switching Regulators
U
DESCRIPTIO
EATURE
S
F
■
■
■
■
■
■
■
■
■
Wide Input Voltage Range: 3.5V to 30V
Low Quiescent Current: 7mA
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
extremelyeasytouseandprovides“bustproof”operation
similar to that obtained with 3-pin linear regulators.
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)
O U
PPLICATI
S
A
■
■
■
■
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
TheLT1270A/LT1270useadaptiveanti-satswitchdriveto
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.
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.
U
O
TYPICAL APPLICATI
Maximum Output Power*
High Efficiency† Buck Converter
100
BOOST
†EFFICIENCY IS ≈ 88% @ 2A, 86% @ 5A.
V
IN
(8V TO 25V)
FOµRPOWER SHUTDOWN OPTION, CONSULT FACTORY.
BUCK-BOOST,
= 12V
V
V
80
60
SW
V
*THESE COMPONENTS RATED CONSERVATIVELY TO
IMPROVE EFFICIENCY. MAXIMUM OUTPUT CURRENT
CAN BE 7A. FOR HIGH EFFICIENCY, THE INDUCTOR SHOULD
BE MOLYPERMALLOY OR FERRITE.
O
1N5819
LT1270*
(INVERTING)
FB
IN
FLYBACK†
GND
V
C
+
1µF
0.047µF
0.047µF
40
1k
35µH, 8A*
5V*
5A
BUCK-BOOST, V = 5V
O
20
0
(INVERTING)
9.1k
10k
ANODE
+
LT1431CZ REF
CATHODE
470µF
35V
MBR1035*
2N3904
0
5
15
20
25
30
10
INPUT VOLTAGE (V)
LT1270 • TA02
1N4158
560Ω
1000µF
*MULTIPLY BY 1.2 FOR LT1270A.
360Ω
25V
BUCK MODE OUTPUT POWER ≈ (7.5A)(V
)
OUT
† TRANSFORMER TURNS RATIO MUST BE
OPTIMUM TO ACHIEVE FULL POWER
LT1270 • TA01
1
LT1270A/LT1270
W W W
U
ABSOLUTE AXI U RATI GS
/O
PACKAGE RDER I FOR ATIO
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
FRONT VIEW
ORDER PART
NUMBER
5
4
3
2
1
V
V
GND
FB
IN
SW
LT1270CT
LT1270ACT
V
C
T PACKAGE
5-LEAD TO-220
TJMAX = 100°C, θJA = 2°C/W, θJA = 50°C/W
ELECTRICAL CHARACTERISTICS
VIN = 15V, VC = 0.5V, VFB = VREF, switch pin open, unless otherwise noted.
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
V
REF
Reference Voltage
Measured at Feedback Pin
C
1.224
1.214
1.244
1.244
1.264
1.274
V
V
V = 0.8V
●
I
Feedback Input Current
V
= V
REF
350
4400
200
750
nA
nA
B
FB
1100
gm
Error Amplifier
Transconductance
∆l = ±25µA
3000
2400
6000
7000
µmho
µmho
C
●
●
Error Amplifier Source of
Sink Current
V = 1.5V
C
150
120
350
400
µA
µA
Error Amplifier Clamp Voltage
Hi Clamp, V = 1V
1.80
0.25
2.30
0.52
V
V
FB
Lo Clamp, V = 1.5V
0.38
FB
Reference Voltage Line Regulation
Error Amplifier Voltage Gain
Minimum Input Voltage
Supply Current
3V ≤ V ≤ V
, V = 0.8V
●
●
0.03
%/V
V/V
V
IN
MAX
C
A
0.9V ≤ V ≤ 1.4V
500
800
2.8
7
V
C
3.0
10
I
3V ≤ V ≤ V
, V = 0.6V
C
mA
Q
IN
MAX
Control Pin Threshold
Duty Cycle = 0
0.80
0.60
0.90
1.08
1.25
V
V
●
●
Normal/Flyback Threshold
on Feedback Pin
0.40
0.45
16.3
6.8
0.54
V
V
V
Flyback Reference Voltage
I
= 50µA
FB
15.0
14.0
17.6
18.0
V
V
FB
Change in Flyback Reference
Voltage
0.05 ≤ I ≤ 1mA
4.5
8.5
0.03
650
V
FB
FB
Flyback Reference Voltage
Line Regulation
I
= 50µA
0.01
300
%/V
FB
3V ≤ V ≤ V
IN
MAX
Flyback Amplifier
Transconductance (gm)
∆l = ±10µA
C
150
µmho
Flyback Amplifier Source
and Sink Current
V = 0.6V Source
FB
●
●
15
25
32
40
70
70
µA
µA
C
I
= 50µA Sink
BV
Output Switch Breakdown
Voltage
3V ≤ V ≤ V
SW
●
60
75
0.12
12
V
IN
MAX
I
= 5mA
V
SAT
Output Switch ON
Resistance (Note 1, 3)
T ≤ 100°C
0.18
0.22
Ω
Ω
J
T ≤ 125°C
J
Control Voltage to Switch
Current Transconductance
A/V
2
LT1270A/LT1270
ELECTRICAL CHARACTERISTICS VIN = 15V, VC = 0.5V, VFB = VREF, switch pin open, unless otherwise noted.
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
I
Switch Current Limit (LT1270)
(Note 3)
Duty Cycle = 50%, T ≤ 100°C
●
●
8
6
16
14
A
A
LIM
J
Duty Cycle = 80%, T ≤ 100°C
J
I
Switch Current Limit (LT1270A)
(Note 3)
Duty Cycle = 50%, T ≤ 100°C
●
●
10.0
7.5
16.0
14.0
A
A
LIM
J
Duty Cycle = 80%, T ≤ 100°C
J
∆I
SW
Supply Current Increase
During Switch-ON Time
25
60
40
mA/A
IN
∆I
f
Switching Frequency
50
50
70
70
kHz
kHz
●
DC
Maximum Switch Duty Cycle
Flyback Sense Delay Time
80
92
1.5
100
150
95
%
µs
µA
MAX
Shutdown Mode Supply Current
Shutdown Mode Threshold Voltage
3V ≤ V ≤ V
, V = 0.05V
C
400
IN
MAX
MAX
3V ≤ V ≤ V
100
50
250
300
mV
mV
IN
●
The
● denotes specifications which apply over the full operating
switch current is given by I = 6.67 (1.7 – DC) for the LT1270 and I
=
LIM
LIM
temperature range.
8.33 (1.7 – DC) for the LT1270A.
Note 1: Measured with V in Hi Clamp, V = 0.8V.
Note 2: For duty cycles (DC) between 50% and 80%, minimum guaranteed
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.
C
FB
U W
TYPICAL PERFOR A CE CHARACTERISTICS
Switch Saturation Voltage
Switch Current Limit vs Duty Cycle
1.6
1.2
0.8
0.4
0
2.4
T
= 25°C
J
1.8
25°C
–55°C
1.2
125°C
6
0
0
2
4
6
8
10
0
20
40
60
80
100
SWITCH CURRENT (A)
DUTY CYCLE (%)
LT1270 • TA04
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 represen-
tation that the interconnection of circuits as described herein will not infringe on existing patent rights.
3
LT1270A/LT1270
U
TYPICAL APPLICATIO S
Negative-to-Positive Buck-Boost Converter
Boost Converter (5V to 12V)
5V
L2
55µH*
OPTIONAL
OUTPUT
FILTER
C3
R1
L1
V
55µH**
IN
V
SW
FB
MBR1020
D1
V
IN
12V, 2A
LT1270
V
OUT
12V, 3A
V
SW
FB
+
10.7k
C2
11.3k
2000µF
LT1270
+
GND
V
C
+
1000µF
C4
200µF*
25V
1k
1.24k
OPTIONAL
INPUT
GND
V
C
+
FILTER
1µF
R3
2.2k
1.24k
L3
PULSE ENGINEERING #PE-92116
LT1270 • TA05
C1
*REQUIRED IF INPUT LEADS ≥ 2"
**PULSE ENGINEERING #PE-92116
0.22µF
V
IN
–12V
LT1270 • TA06
Negative Buck Converter
+
C2
R1
D1
1000µF
4.64k
L1
LOAD
100µH**
V
IN
–5.2V, 7.5A
V
SW
12k
LT1270
+
C3
100µF*
OPTIONAL
INPUT FILTER
L3
FB
GND
V
C
OPTIONAL
OUTPUT
FILTER
10µH
C1
R3
+
R2
1.24k
C4
200µF
L2
4µF
V
IN
–20V
*REQUIRED IF INPUT LEADS ≥ 2"
**PULSE ENGINEERING #PE-92115
LT1270 • TA07
U
PACKAGE DESCRIPTIO
Dimensions in inches (millimeters) unless otherwise noted.
0.380 – 0.420
0.079 – 0.135
(2.007 – 3.429)
(9.652 – 10.668)
0.139 – 0.153
(3.531 – 3.886)
DIA
0.169 – 0.185
(4.293 – 4.699)
0.035 – 0.055
(0.889 – 1.397)
0.560 – 0.650
(14.224 – 16.510)
0.460 – 0.500
(11.68 – 12.70)
0.620 ± 0.020
(15.75 ± 0.508)
0.866 – 0.913
(21.996 – 23.190)
0.700 – 0.728
(17.780 – 18.491)
0.970 – 1.050
(24.64 – 26.67)
0.055 – 0.090
(1.397 – 2.286)
0.079 – 0.115
(2.007 – 2.921)
0.015 – 0.025
(0.381 – 0.635)
0.210 – 0.240
(5.334 – 6.096)
0.327 – 0.335
(8.306 – 8.509)
0.057 – 0.077
(1.448 – 1.956)
0.028 – 0.035
(0.711 – 0.889)
0.170 – 0.185
(4.318 – 4.699)
T5 (FORMED) 0392
LT/GP 1292 5K REV B
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7487
4
●
●
LINEAR TECHNOLOGY CORPORATION 1992
(408) 432-1900 FAX: (408) 434-0507 TELEX: 499-3977
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