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LT1268B/LT1268 7.5A, 150kHz Switching Regulators
FEATURES
s s s s s s
DESCRIPTIO
s
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)
APPLICATI
s s s s
S
High Efficiency Boost Converter PC Power Supply with Multiple Outputs Battery Upconverter Negative-to-Positive Converter
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. 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. 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 100A typical for standby operation.
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.
TYPICAL APPLICATI
VIN 4.7V TO 5.3V L1 8H, 5A* D2, D3 1N4001
Boost Regulator with 5.3V 1% Output
D1 MBR1035 L2 2H, 5A**
100
VOUT 5.3V 1% 3.75A
EFFICIENCY (%)
90 VIN = 4.7V
+
C3 390F 16V
C5 0.02
+
C1 220F 16V
VIN
VSW LT1268B FB
R1 4.043k 0.1%
+
C4 390F 16V
80
CASE GND
VC C2 0.068 R3 220 R2 1.24k 0.1%
70
60
LT1268 * TA01
*COILTRONICS CTX8-5-52 **COILTRONICS CTX2-5-52 OPTIONAL. D2 AND D3 ARE USED TO INCREASE UNDERVOLTAGE LOCKOUT FROM 2.7V TO 4V.
U
Efficiency of 5.3V Boost Converter
VIN = 5.3V VIN = 5V 0 1 2 LOAD CURRENT (A)
LT1268 * TA02
UO
UO
3
4
1
LT1268B/LT1268 ABSOLUTE AXI U RATI GS
PACKAGE/ORDER I FOR ATIO
FRONT VIEW 5 4 3 2 1 Q PACKAGE 5-LEAD DD VIN VSW GND FB VC
Supply Voltage ....................................................... 30V Switch Output Voltage ............................................ 60V Feedback Pin Voltage (Transient, 1ms) ................ 15V Operating Junction Temperature Range Operating ............................................... 0C to 125C Short-Circuit ......................................... 0C to 140C Storage Temperature Range ................. - 65C to 150C Lead Temperature (Soldering, 10 sec).................. 300C
ORDER PART NUMBER LT1268CQ LT1268BCQ
TJMAX = 125C, JC = 2C/ W, JA = See Notes 5 and 6
FRONT VIEW 5 4 3 2 1 T PACKAGE 5-LEAD TO-220 TJMAX = 125C, JC = 2C/W, JA = 50C/W VIN VSW GND FB VC
ORDER PART NUMBER LT1268CT LT1268BCT
Consult factory for Industrial and Military parts
ELECTRICAL CHARACTERISTICS
SYMBOL VREF PARAMETER Reference Voltage Measured at Feedback Pin (Note 4) Reference Voltage IB gm Feedback Input Current Error Amplifier Transconductance Error Amplifier Source or Sink Current Error Amplifier Clamp Voltage Reference Voltage Line Regulation AV IQ Error Amplifier Voltage Gain Minimum Input Voltage Supply Current Control Pin Threshold BV VSAT Output Switch Breakdown Voltage Output Switch-ON Resistance (Note 1, 3) Control Voltage to Switch Current Transconductance ILIM Switch Current Limit (Note 3, 6)
VIN = 15V, VC = 0.5V, VFB = VREF, switch pin open, unless otherwise noted.
MIN
q
CONDITIONS LT1268B LT1268
q
TYP 1.244 1.244 1.244 1.244 350
MAX 1.253 1.264 1.264 1.274 750 1100 6000 7000 350 400 2.30 0.52 0.03
UNITS V V V V nA nA mho mho A A V V %/V V/V V mA V V V A/V
1.235 1.224 1.224 1.214
VFB = VREF
q
IC = 25A
q
3000 2400 150 120 1.80 0.25
4400 200
VC = 1.5V
q
Hi Clamp, VFB = 1V Lo Clamp, VFB = 1.5V 3V VIN VMAX, VC = 0.8V 0.9V VC 1.4V
q q
0.38 800 2.8 7
500
3.0 10 1.08 1.25 0.18 0.22
3V VIN VMAX, VC = 0.6V Duty Cycle = 0
q
0.7 0.5 60
0.9 75 0.12 12
3V VIN VMAX, ISW = 1.5mA TJ 100C TJ 125C
q
Duty Cycle = 50%, TJ 100C Duty Cycle = 65%, TJ 100C
q q
7.50 6.50
15 14
2
U
A A
W
U
U
WW
W
LT1268B/LT1268
ELECTRICAL CHARACTERISTICS
SYMBOL IIN ISW f DCMAX PARAMETER Supply Current Increase During Switch-ON Time Switching Frequency
VIN = 15V, VC = 0.5V, VFB = VREF, switch pin open, unless otherwise noted.
MIN TYP 25 120 120 65 150 85 100
q
CONDITIONS
MAX 45 180 180 92 500 250 300
UNITS mA/A kHz kHz % A mV mV
q
Maximum Switch Duty Cycle Shutdown Mode Supply Current Shutdown Mode Threshold Voltage 3V VIN VMAX, VC = 0.05V 3V VIN VMAX
100 50
150
The q 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 125C. 100C test limits are guaranteed by correlation to 125C 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
has a thermal resistance of 20C/W to 50C/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.
IMAX =
P RSW x DC
P = Power dissipation due to switch current RSW = Switch-ON resistance 0.15 DC = Switch duty cycle In a typical application where thermal resistance is 30C/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
IMAX = 1.5 = 5A 0.15 x 0.4
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.
TYPICAL PERFOR A CE CHARACTERISTICS
Switch Current Limit vs Duty Cycle
24 1.6
SWITCH SATURATION VOLTAGE (V)
SWITCH CURRENT (A)
18
12 25C 6
-55C 125C
0.8 0.6 0.4 0.2 0 0 1 2 345678 SWITCH CURRENT (A) 9 10
(C/W)
0
0
10 20
30 40 50 60 70 80 90 100 DUTY CYCLE (%)
LT1268 * TPC01
UW
Switch Saturation Voltage
60 TJ = 25C 50 1.4 1.2 1.0 40 30 20 10 0
Q Package Thermal Resistance
SINGLE-SIDED BOARD, 1oz COPPER
DOUBLE-SIDED BOARD, 1oz COPPER BOTTOM COPPER AREA >100cm2
0
25 10 15 20 5 TOP SURFACE COPPER AREA (cm2)
30
LT1268 * TPC02
LT1268 * 603
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.
3
LT1268B/LT1268
TYPICAL APPLICATI
PACKAGE DESCRIPTIO
0.060 (1.524)
Q Package 5-Lead DD
(
+0.012 0.331 -0.020
+0.305 8.407 -0.508
(
+0.012 0.143 -0.020
+0.305 3.632 -0.508
0.380 - 0.420 (9.652 - 10.668) 0.139 - 0.153 (3.531 - 3.886) DIA
T Package 5-Lead TO-220
0.560 - 0.650 (14.224 - 16.510) 0.866 - 0.913 (21.996 - 23.190)
0.057 - 0.077 (1.448 - 1.956)
4
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7487
(408) 432-1900 q FAX: (408) 434-0507 q TELEX: 499-3977
U
UO
Boost Converter (5V TO 12V)
5V 20H VIN VSW MBR1020 LT1268CT 10.7k FB GND VC 1k 1.24k 12V, 1.5A
+
1000F 25V
+
1F
LT1268 * TA03
Dimensions in inches (millimeters) unless otherwise noted.
0.401 0.015 (10.185 0.381) 15 TYP
0.175 0.008 (4.445 0.203)
0.050 0.008 (1.270 0.203)
+0.008 0.004 -0.004
)
0.067 0.010 (1.702 0.254) 0.032 0.008 (0.813 0.203)
0.059 (1.499) TYP
(
+0.203 0.102 -0.102
)
0.105 0.008 (2.667 0.203)
)
0.022 0.005 (0.559 0.127)
0.050 0.012 (1.270 0.305)
0.079 - 0.135 (2.007 - 3.429)
0.169 - 0.185 (4.293 - 4.699)
0.035 - 0.055 (0.889 - 1.397)
0.460 - 0.500 (11.68 - 12.70)
0.620 0.020 (15.75 0.508) 0.700 - 0.728 (17.780 - 18.491)
0.970 - 1.050 (24.64 - 26.67)
0.028 - 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
(c) LINEAR TECHNOLOGY CORPORATION 1994

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