Datasheet LT1268B, LT1268 Datasheet (Linear Technology)

LT1268B/LT1268

LOAD CURRENT (A)

0

EFFICIENCY (%)

80

90

4

LT1268 • TA02

70

60

1

2

3

100

VIN = 5.3V

VIN = 4.7V

VIN = 5V

7.5A, 150kHz

Switching Regulators

EATU

F

■

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

RE

S

5-Pin Packages

■

Can Be Externally Synchronized
(See LT1072 Data Sheet)

U

O

PPLICATI

A

■

High Efficiency Boost 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 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.

S

DUESCRIPTIO

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 100µA typical for standby operation.

V

IN

4.7V TO

5.3V

U

O

A

PPLICATITYPICAL

Boost Regulator with 5.3V ±1% Output

†

V

MBR1035

SW

FB

C

R3
220Ω

D1

C2

0.068

C3

+

390µF
16V

C1

+

220µF
16V

L1

8µH, 5A*

D2, D3
1N4001

V

IN

LT1268B

CASE

GND V

COILTRONICS CTX8-5-52

*

COILTRONICS CTX2-5-52

**

†

OPTIONAL. D2 AND D3 ARE USED TO INCREASE
UNDERVOLTAGE LOCKOUT FROM 2.7V TO ≈4V.

L2

2µH, 5A**

C5

0.02

R1

4.043k

0.1%

R2

1.24k

0.1%

LT1268 • TA01

V

OUT

5.3V ±1%

3.75A

C4

+

390µF
16V

Efficiency of 5.3V Boost Converter

1

LT1268B/LT1268

Q PACKAGE

5-LEAD DD

FRONT VIEW

V

IN

V

SW

GND
FB
V

C

5
4
3
2
1

A

W

O

LUTEXI TIS

S

A

WUW

U

ARB

G

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

LECTRICAL C CHARA TERIST

E

ICS

VIN = 15V, VC = 0.5V, VFB = V

/

PACKAGE

T

= 125°C, θJC = 2°C/W, θJA = See Notes 5 and 6

JMAX

T

= 125°C, θJC = 2°C/W, θJA = 50°C/W

JMAX

Consult factory for Industrial and Military parts

O

RDER I FOR ATIO

FRONT VIEW

5
4
3
2
1

T PACKAGE

5-LEAD TO-220

, switch pin open, unless otherwise noted.

REF

V

IN

V

SW

GND
FB
V

C

WU

ORDER PART

NUMBER

LT1268CQ
LT1268BCQ

ORDER PART

NUMBER

LT1268CT
LT1268BCT

U

SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS

V

REF

I

B

g

m

A

V

I

Q

BV Output Switch Breakdown Voltage 3V ≤ VIN ≤ V
V

SAT

I

LIM

2

Reference Voltage Measured at LT1268B 1.235 1.244 1.253 V
Feedback Pin (Note 4)

Reference Voltage LT1268 1.224 1.244 1.264 V

Feedback Input Current VFB = V

Error Amplifier Transconductance ∆IC = ±25µA 3000 4400 6000 µmho

Error Amplifier Source or Sink Current VC = 1.5V 150 200 350 µA

Error Amplifier Clamp Voltage Hi Clamp, VFB = 1V 1.80 2.30 V

Reference Voltage Line Regulation 3V ≤ VIN ≤ V
Error Amplifier Voltage Gain 0.9V ≤ VC ≤ 1.4V 500 800 V/V
Minimum Input Voltage ● 2.8 3.0 V
Supply Current 3V ≤ VIN ≤ V
Control Pin Threshold Duty Cycle = 0 0.7 0.9 1.08 V

Output Switch-ON Resistance TJ ≤ 100°C 0.12 0.18 Ω
(Note 1, 3) TJ ≤ 125°C 0.22 Ω

Control Voltage to Switch 12 A/V
Current Transconductance

Switch Current Limit (Note 3, 6) Duty Cycle = 50%, TJ ≤ 100°C ● 7.50 15 A

REF

Lo Clamp, VFB = 1.5V 0.25 0.38 0.52 V

, VC = 0.8V ● 0.03 %/V

MAX

, VC = 0.6V 7 10 mA

MAX

, ISW = 1.5mA ● 60 75 V

MAX

Duty Cycle = 65%, T

≤ 100°C ● 6.50 14 A

J

● 1.224 1.244 1.264 V

● 1.214 1.244 1.274 V

350 750 nA

● 1100 nA

● 2400 7000 µmho

● 120 400 µA

● 0.5 1.25 V

LT1268B/LT1268

LECTRICAL C CHARA TERIST

E

ICS

VIN = 15V, VC = 0.5V, VFB = V

, switch pin open, unless otherwise noted.

REF

SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS

∆I
∆I

IN

SW

Supply Current Increase 25 45 mA/A
During Switch-ON Time

f Switching Frequency 120 150 180 kHz

● 120 180 kHz

DC

MAX

The ● denotes specifications which apply over the full operating
temperature range.

Note 1: Measured with V
Note 2: For duty cycles (DC) between 50% and 65%, minimum guaranteed

switch current is given by I
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

Maximum Switch Duty Cycle 65 85 92 %
Shutdown Mode Supply Current 3V ≤ VIN ≤ V
Shutdown Mode Threshold Voltage 3V ≤ VIN ≤ V

, VC = 0.05V 100 500 µA

MAX
MAX

● 50 300 mV

100 150 250 mV

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

in hi clamp, VFB = 0.8V.

C

= 6.25 (1.7 – DC).

LIM

function of power loss and duty cycle. See AN19 for more details.

I

MAX

=

P

R

× DC

SW

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

I

= = 5A

MAX

1.5

0.15 × 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.

WU

TYPICAL PERFOR A CE CHARACTERISTICS

Switch Current Limit vs Duty Cycle

24

18

12

SWITCH CURRENT (A)

6

0

10

20

0

30

25°C

40

DUTY CYCLE (%)

125°C

50

60

70

–55°C

80

90

100

LT1268 • TPC01

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.

Switch Saturation Voltage Q Package Thermal Resistance

1.6
TJ = 25°C

1.4

1.2

1.0

0.8

0.6

0.4

SWITCH SATURATION VOLTAGE (V)

0.2

0

1

2

0

SWITCH CURRENT (A)

5

6

7

3

4

8

LT1268 • TPC02

60

50

SINGLE-SIDED BOARD, 1oz COPPER

40

30

θ (°C/W)

20

10

9

10

0

DOUBLE-SIDED BOARD, 1oz COPPER
BOTTOM COPPER AREA >100cm

0

10 15 20

5

TOP SURFACE COPPER AREA (cm2)

2

25 30

LT1268 • 603

3

LT1268B/LT1268

U

O

A

PPLICATITYPICAL

PACKAGE DESCRIPTIO

Boost Converter (5V TO 12V)

5V

20µH

V

IN

V

LT1268CT

GND

SW

FB

V

C

1k 1.24k

+

1µF

MBR1020

10.7k

+

1000µF
25V

12V, 1.5A

LT1268 • TA03

U

Dimensions in inches (millimeters) unless otherwise noted.

Q Package
5-Lead DD

T Package

5-Lead TO-220

0.060

(1.524)

+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)

0.560 – 0.650

(14.224 – 16.510)

0.139 – 0.153

(3.531 – 3.886)

DIA

0.032 ± 0.008

(0.813 ± 0.203)

0.401 ± 0.015

(10.185 ± 0.381)

15° TYP

0.067 ± 0.010

(1.702 ± 0.254)

0.079 – 0.135

(2.007 – 3.429)

0.866 – 0.913

(21.996 – 23.190)

0.970 – 1.050

(24.64 – 26.67)

0.175 ± 0.008

(4.445 ± 0.203)

0.059

(1.499)

0.022 ± 0.005

(0.559 ± 0.127)

0.169 – 0.185

(4.293 – 4.699)

0.460 – 0.500

(11.68 – 12.70)

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)

0.050 ± 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)

4

0.057 – 0.077

(1.448 – 1.956)

Linear Technology Corporation

1630 McCarthy Blvd., Milpitas, CA 95035-7487

(408) 432-1 900

●

FAX

: [phone]

●

TELEX

: 499-3977

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

 LINEAR TECHNOLOGY CORPORATION 1994