LINEAR TECHNOLOGY LT3460 Technical data

查询LT3460供应商

FEATURES

■

1.3MHz Switching Frequency

■

High Output Voltage: Up to 36V

■

300mA Integrated Switch

■

12V at 70mA from 5V Input

■

5V at 60mA from 3.3V Input

■

Wide Input Range: 2.5V to 16V

■

Uses Small Surface Mount Components

■

Low Shutdown Current: <1µA

■

Low Profile (1mm) SC70 and SOT-23 (ThinSOTTM)
Packages

U

APPLICATIO S

■

Digital Cameras

■

CCD Bias Supply

■

XDSL Power Supply

■

TFT-LCD Bias Supply

■

Local 5V or 12V Supply

■

Medical Diagnostic Equipment

■

Battery Backup

LT3460

1.3MHz Step-Up DC/DC

Converter in SC70 and ThinSOT

U

DESCRIPTIO

The LT®3460 is a general purpose step-up DC/DC con­verter. The LT3460 switches at 1.3MHz, allowing the use
of tiny, low cost and low height capacitors and inductors.
The constant frequency results in low, predictable output
noise that is easy to filter.

The high voltage switch in the LT3460 is rated at 38V,
making the device ideal for boost converters up to 36V.
The LT3460 can generate 12V at up to 70mA from a 5V
supply.

The LT3460 is available in SC70 and SOT-23 packages.

, LTC and LT are registered trademarks of Linear Technology Corporation.

ThinSOT is a trademark of Linear Technology Corporation

TYPICAL APPLICATIO

5V to 12V, 70mA Step-Up DC/DC Converter

V

IN

SHDN

22µH

SW

LT3460

FB

GND

V

IN

5V

4.7µF

OFF ON

U

130k

15k

22pF

V
12V
70mA

1µF

3460 F01

OUT

90

85

80

75

EFFICIENCY (%)

70

65

60

V

SW

5V/DIV

100mA/DIV

Efficiency

0

20 40 60 80

LOAD CURRENT (mA)

3460 F01a

Switching Waveforms

I

L

0.2µs/DIV

3460 F01b

3460f

1

LT3460

6 V

IN

5 GND
4 SHDN

SW 1

TOP VIEW

SC6 PACKAGE

6-LEAD PLASTIC SC70

GND 2

FB 3

WW

W

ABSOLUTE AXI U RATI GS

U

(Note 1)

Input Voltage (VIN) .................................................. 16V

SW Voltage .............................................................. 38V

FB Voltage ................................................................. 5V

SHDN Voltage .......................................................... 16V

UUW

PACKAGE/ORDER I FOR ATIO

ORDER PART

TOP VIEW

SW 1

GND 2

FB 3

S5 PACKAGE

5-LEAD PLASTIC TSOT-23

T

= 125°C, θJA = 256°C/W IN FREE AIR

JMAX

= 120°C ON BOARD OVER

θ

JA

GROUND PLANE

5 V

IN

4 SHDN

NUMBER

LT3460ES5

S5 PART MARKING

LTB1

Operating Ambient

Temperature Range (Note 2) .................. – 40°C to 85°C

Maximum Junction Temperature .......................... 125°C

Storage Temperature Range ................. –65°C to 150°C

Lead Temperature (Soldering, 10 sec)..................300°C

ORDER PART

NUMBER

LT3460ESC6

SC6 PART MARKING

T

= 125°C, θJA = 400°C/W IN FREE AIR

JMAX

θ

= 270°C/W ON BOARD OVER GROUND

JA

PLANE

LAAF

Consult LTC Marketing for parts specified with wider operating temperature ranges.

ELECTRICAL CHARACTERISTICS

temperature range, otherwise specifications are at TA = 25°C, VIN = 3V, V

PARAMETER CONDITIONS MIN TYP MAX UNITS

Minimum Operating Voltage 2.5 V
Maximum Operating Voltage 16 V
Feedback Voltage 1.235 1.255 1.275 V

Feedback Line Regulation 2.5V < VIN < 16V 0.015 %/V
FB Pin Bias Current ● 52580 nA
Supply Current 2.0 3.0 mA

Switching Frequency 1.0 1.3 1.7 MHz
Maximum Duty Cycle 85 90 %
Switch Current Limit 300 420 600 mA
Switch V

CESAT

Switch Leakage Current VSW = 5V 0.01 1 µA
SHDN Voltage High 1.5 V
SHDN Voltage Low 0.4 V
SHDN Pin Bias Current 40 µA

Note 1: Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.

The ● denotes the specifications which apply over the full operating

= 3V, unless otherwise noted.

SHDN

● 1.225 1.280 V

SHDN = 0V 0.1 0.5 µA

ISW = 250mA 320 450 mV

Note 2: The LT3460E is guaranteed to meet specifications from 0°C to
70°C. Specifications over the –40°C to 85°C operating temperature range
are assured by design, characterization and correlation with statistical
process controls.

3460f

2

TEMPERATURE (°C)

–50

250

300

350

25 75

3460 G03

200

150

100

–25 0

50 100

50

0

SHDN PIN BIAS CURRENT (µA)

400

SHDN = 3V

SHDN = 16V

UW

TYPICAL PERFOR A CE CHARACTERISTICS

LT3460

Quiescent Current

2.5

2.0

1.5

IQ (mA)

1.0

0.5

0

0

–50°C

25°C

100°C

5

10

VIN (V)

Feedback Bias Current

30

25

20

15

10

FEEDBACK BIAS CURRENT (nA)

5

15

3460 G01

Switching Frequency

1.4

1.2

1.0

0.8

0.6

0.4

SWITCHING FREQUENCY (MHz)

0.2

0

–50

–25 0

TEMPERATURE (°C)

50 100

25 75

Feedback Voltage

1.260

1.255

1.250

VFB (V)

1.245

SHDN Pin Bias Current

3460 G02

0

–50

–25 0

TEMPERATURE (°C)

50 100

25 75

3460 G04

1.240
–50

–25 0

TEMPERATURE (°C)

50 100

25 75

3460 G05

Switch Saturation Voltage
(V

) Current Limit vs Duty Cycle

CESAT

400

350

IC = 250mA

300

250

200

150

100

50

0

–50

IC = 200mA

IC = 100mA

–25 0

50 100

25 75

TEMPERATURE (°C)

3460 G06

(mV)

CESAT

V

450

400

350

300

250

200

150

CURRENT LIMIT (mA)

100

50

0

0

0.2 0.4

0.6

DUTY CYCLE

0.8 1.0

3460 G07

3460f

3

LT3460

U

PI FU CTIO S

UU

(ThinSOT/SC70 Packages)

SW (Pin 1/Pin 1): Switch Pin. Connect inductor/diode

here. Minimize trace at this pin to reduce EMI.
GND (Pin 2/Pins 2 and 5): Ground Pin. Tie directly to local

ground plane.
FB (Pin 3/Pin 3): Feedback Pin. Reference

voltage is 1.255V. Connect resistor divider tap here.
Minimize trace area at FB. Set V
V

= 1.255V (1 + R1/R2).

OUT

according to

OUT

W

BLOCK DIAGRA

R

C

C

C

∑

RAMP

1.3MHz

COMPARATOR

–

+

V

IN

(PIN 6 SC70 PACKAGE)

V

SHUTDOWN

RS, CS OPTIONAL SOFT-START COMPONENTS

R

5 1

OUT

R1 (EXTERNAL)

FB

R2 (EXTERNAL)

(EXTERNAL)

S

1.255V

REFERENCE

4

SHDN

C

(EXTERNAL)

S

+

A1

–

3

FB

GENERATOR

OSCILLATOR

SHDN (Pin 4/Pin 4): Shutdown Pin. Tie to 1.5V or higher
to enable device; 0.4V or less to disable device. Also
functions as soft-start. Use RC filter (47k, 47nF typ) as
shown in Figure 1.

V

(Pin 5/Pin 6): Input Supply Pin. Must be locally

IN

bypassed.

DRIVER

A2

R

Q

S

+

–

SW

Q1

0.1Ω

GND

2

(PINS 2 AND 5 SC70 PACKAGE)

3460 BD

Figure 1. Block Diagram

U

OPERATIO

The LT3460 uses a constant frequency, current mode
control scheme to provide excellent line and load regula­tion. Operation can be best understood by referring to the
block diagram in Figure 1. At the start of each oscillator
cycle, the SR latch is set, which turns on the power switch
Q1. A voltage proportional to the switch current is added
to a stabilizing ramp and the resulting sum is fed into the
positive terminal of the PWM comparator A2. When this
voltage exceeds the level at the negative input of A2, the SR

4

latch is reset turning off the power switch. The level at the
negative input of A2 is set by the error amplifier A1, and is
simply an amplified version of the difference between the
feedback voltage and the reference voltage of 1.255V. In
this manner, the error amplifier sets the correct peak
current level to keep the output in regulation. If the error
amplifier’s output increases, more current is delivered to
the output; if it decreases, less current is delivered.

3460f