LINER LT1268B

LT1268B/LT1268
7.5A, 150kHz
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 7.5A Switch
Very Few External Parts Required
Self-Protected Against Overloads
Available in Standard and Surface Mount
5-Pin Packages
Can Be Externally Synchronized
(See LT1072 Data Sheet)
The LT1268B and LT1268 are monolithic high power
switching regulators. Identical to the popular LT1070,
except for switching frequency (150kHz) 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 LT1268 to be built in standard 5-pin power packages.
This makes it extremely easy to use and provides “bust
proof” operations similar to that obtained with 3-pin
linear regulators.
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APPLICATI
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S
High Efficiency Boost Converter
PC Power Supply with Multiple Outputs
Battery Upconverter
Negative-to-Positive Converter
The LT1268 operate with supply voltages from 3.5V to
30V and draw only 7mA quiescent current. By utilizing
current mode switching techniques, it provides excellent
AC and DC load and line regulation.
USER NOTE:
This data sheet is only intended to provide specifications, graphs, and a general functional
description of the LT1268B/LT1268. Application circuits are included to show the capability of the
LT1268B/LT1268. A complete design manual (AN19) 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 LT1268B/LT1268 factoring in the higher switch
current rating and higher operating frequency.
The LT1268 use an 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.
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TYPICAL APPLICATI
Boost Regulator with 5.3V ±1% Output
D2, D3†
1N4001
+
C1
220µF
16V
VIN
Efficiency of 5.3V Boost Converter
100
L2
2µH, 5A**
+
C3
390µF
16V
C5
0.02
VSW
VOUT
5.3V ±1%
3.75A
R1
4.043k
0.1%
+
LT1268B FB
CASE GND
VC
C2
0.068
R3
220Ω
*COILTRONICS CTX8-5-52
**COILTRONICS CTX2-5-52
†
OPTIONAL. D2 AND D3 ARE USED TO INCREASE
UNDERVOLTAGE LOCKOUT FROM 2.7V TO ≈4V.
R2
1.24k
0.1%
C4
390µF
16V
VIN = 4.7V
VIN = 5V
80
70
60
LT1268 • TA01
VIN = 5.3V
90
EFFICIENCY (%)
L1
8µH, 5A*
VIN
4.7V TO
5.3V
D1
MBR1035
0
1
2
3
4
LOAD CURRENT (A)
LT1268 • TA02
1
LT1268B/LT1268
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RATI GS
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W W
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AXI U
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ABSOLUTE
PACKAGE/ORDER I FOR ATIO
Supply Voltage ....................................................... 30V
Switch Output Voltage ............................................ 60V
Feedback Pin Voltage (Transient, 1ms) ................ ±15V
Operating Junction Temperature Range
Operating ............................................... 0°C to 125°C
Short-Circuit ......................................... 0°C to 140°C
Storage Temperature Range ................. – 65°C to 150°C
Lead Temperature (Soldering, 10 sec).................. 300°C
FRONT VIEW
5
4
3
2
1
ORDER PART
NUMBER
VIN
VSW
GND
FB
VC
LT1268CQ
LT1268BCQ
Q PACKAGE
5-LEAD DD
TJMAX = 125°C, θJC = 2°C/ W, θJA = See Notes 5 and 6
FRONT VIEW
VIN
VSW
GND
FB
VC
5
4
3
2
1
T PACKAGE
5-LEAD TO-220
TJMAX = 125°C, θJC = 2°C/W, θJA = 50°C/W
ORDER PART
NUMBER
LT1268CT
LT1268BCT
Consult factory for Industrial and Military parts
ELECTRICAL CHARACTERISTICS
VIN = 15V, VC = 0.5V, VFB = VREF, switch pin open, unless otherwise noted.
SYMBOL
PARAMETER
CONDITIONS
VREF
Reference Voltage Measured at
Feedback Pin (Note 4)
LT1268B
Reference Voltage
LT1268
IB
Feedback Input Current
MIN
TYP
MAX
UNITS
●
1.235
1.224
1.244
1.244
1.253
1.264
V
V
●
1.224
1.214
1.244
1.244
1.264
1.274
V
V
350
750
1100
nA
nA
VFB = VREF
●
gm
Error Amplifier Transconductance
Error Amplifier Source or Sink Current
Error Amplifier Clamp Voltage
AV
∆IC = ±25µA
6000
7000
µmho
µmho
150
120
200
●
350
400
µA
µA
2.30
0.52
V
V
0.03
%/V
VC = 1.5V
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
3000
2400
4400
●
1.80
0.25
●
500
●
Supply Current
3V ≤ VIN ≤ VMAX, VC = 0.6V
Control Pin Threshold
Duty Cycle = 0
BV
Output Switch Breakdown Voltage
3V ≤ VIN ≤ VMAX, ISW = 1.5mA
VSAT
Output Switch-ON Resistance
(Note 1, 3)
TJ ≤ 100°C
TJ ≤ 125°C
2
Switch Current Limit (Note 3, 6)
800
V/V
2.8
3.0
V
7
10
mA
1.08
1.25
0.7
0.5
0.9
●
●
60
75
0.12
Control Voltage to Switch
Current Transconductance
ILIM
0.38
V
0.18
0.22
12
Duty Cycle = 50%, TJ ≤ 100°C
Duty Cycle = 65%, TJ ≤ 100°C
●
●
7.50
6.50
V
V
Ω
Ω
A/V
15
14
A
A
LT1268B/LT1268
ELECTRICAL CHARACTERISTICS
SYMBOL
PARAMETER
∆IIN
∆ISW
Supply Current Increase
During Switch-ON Time
f
Switching Frequency
VIN = 15V, VC = 0.5V, VFB = VREF, switch pin open, unless otherwise noted.
CONDITIONS
MIN
●
DCMAX
Maximum Switch Duty Cycle
Shutdown Mode Supply Current
3V ≤ VIN ≤ VMAX, VC = 0.05V
Shutdown Mode Threshold Voltage
3V ≤ VIN ≤ VMAX
MAX
UNITS
25
45
mA/A
120
120
150
180
180
kHz
kHz
65
85
92
%
100
500
µA
150
250
300
mV
mV
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 65%, minimum guaranteed
switch current is given by ILIM = 6.25 (1.7 – DC).
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.
Note 4: LT1268B reference voltage is specified at ±9mV to guarantee ±1%
output voltage accuracy when 0.1% external resistors are used to set
output voltage. To maintain output accuracy under load, load current
should be taken from the case and the ground pin should be connected
separately to output ground. See AN19 for details.
Note 5: The Q package is intended for surface mount without a separate
heat sink. See graph for thermal resistance as a function of the mounting
area. This curve assumes no other heat dissipators adjacent to package.
Note 6: Maximum switch current may be limited by package power
dissipation, especially for the surface mount (Q) package. This package
TYP
has a thermal resistance of 20°C/W to 50°C/W (see graph). The following
formula will allow an estimate of maximum continuous switch current as a
function of power loss and duty cycle. See AN19 for more details.
P
RSW × DC
IMAX =
P = Power dissipation due to switch current
RSW = Switch-ON resistance ≈ 0.15Ω
DC = Switch duty cycle
In a typical application where thermal resistance is 30°C/W, maximum
power might be limited to 2W and power allocated to switch loss is 1.5W.
For a duty cycle of 40%, this yields
1.5
= 5A
0.15 × 0.4
IMAX =
Obviously, a combination of high thermal resistance and high duty cycle
may restrict switch current to a value well below the 7.5A electrical limit.
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TYPICAL PERFOR A CE CHARACTERISTICS
Switch Current Limit vs Duty Cycle
Switch Saturation Voltage
12
–55°C
25°C
125°C
6
0
10 20
30 40 50 60 70 80 90 100
DUTY CYCLE (%)
LT1268 • TPC01
60
TJ = 25°C
1.4
50
1.2
SINGLE-SIDED BOARD, 1oz COPPER
40
1.0
θ (°C/W)
18
0
Q Package Thermal Resistance
1.6
SWITCH SATURATION VOLTAGE (V)
SWITCH CURRENT (A)
24
0.8
0.6
30
20
DOUBLE-SIDED BOARD, 1oz COPPER
BOTTOM COPPER AREA >100cm2
0.4
10
0.2
0
0
0
1
2
3 4 5 6 7 8
SWITCH CURRENT (A)
9
10
0
LT1268 • TPC02
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 its circuits as described herein will not infringe on existing patent rights.
25
10
15
20
5
TOP SURFACE COPPER AREA (cm2)
30
LT1268 • 603
3
LT1268B/LT1268
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TYPICAL APPLICATI
Boost Converter (5V TO 12V)
5V
20µH
VIN
VSW
MBR1020
12V, 1.5A
LT1268CT
10.7k
FB
GND
+
VC
1k
1000µF
25V
1.24k
+
1µF
LT1268 • TA03
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PACKAGE DESCRIPTIO
Dimensions in inches (millimeters) unless otherwise noted.
0.401 ± 0.015
(10.185 ± 0.381)
0.060
(1.524)
0.175 ± 0.008
(4.445 ± 0.203)
15° TYP
Q Package
5-Lead DD
(
+0.012
0.331 –0.020
+0.305
8.407 –0.508
0.059
(1.499)
TYP
)
0.050 ± 0.008
(1.270 ± 0.203)
(
+0.008
0.004 –0.004
+0.203
0.102 –0.102
)
0.105 ± 0.008
(2.667 ± 0.203)
(
+0.012
0.143 –0.020
+0.305
3.632 –0.508
0.067 ± 0.010
(1.702 ± 0.254)
)
0.380 – 0.420
(9.652 – 10.668)
0.139 – 0.153
(3.531 – 3.886)
DIA
T Package
5-Lead TO-220
0.022 ± 0.005
(0.559 ± 0.127)
0.032 ± 0.008
(0.813 ± 0.203)
0.079 – 0.135
(2.007 – 3.429)
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)
0.050 ± 0.012
(1.270 ± 0.305)
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
Linear Technology Corporation
0.028 – 0.035
(0.711 – 0.889)
0.015 – 0.025
(0.381 – 0.635)
0.210 – 0.240
(5.334 – 6.096)
0.304 – 0.380
(7.722 – 9.652)
0.055 – 0.090
(1.397 – 2.286)
0.079 – 0.115
(2.007 – 2.921)
0.149 – 0.230
(3.785 – 5.842)
1268fs, sn1268 LT/GP 0194 10K REV 0 • PRINTED IN THE USA
1630 McCarthy Blvd., Milpitas, CA 95035-7487
(408) 432-1900 ● FAX: (408) 434-0507 ● TELEX: 499-3977
 LINEAR TECHNOLOGY CORPORATION 1994