Datasheet LT3461, LT3461A Datasheet (LINEAR TECHNOLOGY)

查询LT3461供应商

FEATURES

■

Integrated Schottky Rectifier

■

Fixed Frequency 1.3MHz/3MHz Operation

■

High Output Voltage: Up to 38V

■

Low V

■

12V at 70mA from 5V Input

■

5V at 115mA from 3.3V Input

■

Wide Input Range: 2.5V to 16V

■

Uses Small Surface Mount Components

■

Low Shutdown Current: <1µA

■

Soft-Start

■

Low Profile (1mm) SOT-23 (ThinSOTTM) Package

Switch: 260mV at 250mA

CESAT

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

LT3461/LT3461A

1.3MHz/3MHz Step-Up

DC/DC Converters with

Integrated Schottky in ThinSOT

U

DESCRIPTIO

The LT®3461/LT3461A are general purpose fixed fre­quency current mode step-up DC/DC converters. Both
devices feature an integrated Schottky and a low V
switch allowing a small converter footprint and lower parts
cost. The LT3461 switches at 1.3MHz while the LT3461A
switches at 3MHz. These high switching frequencies en­able the use of tiny, low cost and low height capacitors and
inductors. The constant switching frequency results in
predictable output noise that is easy to filter, and the
inductor based topology ensures an input free from switch­ing noise typically present with charge pump solutions.
The high voltage switch in the LT3461/LT3461A is rated at
40V making the device ideal for boost converters up to
38V.

The LT3461/LT3461A are available in a low profile (1mm)
SOT-23 package.

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

ThinSOT is a trademark of Linear Technology Corporation.

CESAT

TYPICAL APPLICATIO

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

L1

C1
1µF

10µH

6

VINV

4

SHDN

1

SW

LT3461A

GND

2

OUT

5

3

FB

V

IN

5V

OFF ON

U

261k

30.1k

15pF

V

OUT

12V
70mA

C2
1µF

3461 TA01a

85

80

75

70

EFFICIENCY (%)

65

60

0

Efficiency

VIN = 3.3V

20

40

LOAD CURRENT (mA)

VIN = 5V

60

80

3461 TAO1b

3461af

1

LT3461/LT3461A

6 V

IN

5 V

OUT

4 SHDN

SW 1

TOP VIEW

S6 PACKAGE

6-LEAD PLASTIC TSOT-23

GND 2

FB 3

WW

W

ABSOLUTE AXI U RATI GS

(Note 1)

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

, SW Voltage .................................................... 40V

V

OUT

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

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

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UUW

PACKAGE/ORDER I FOR ATIO

ORDER PART

NUMBER

LT3461AES6

LT3461ES6
Operating Ambient

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

T

= 125°C,

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

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

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

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 0.005 %/V

FB Pin Bias Current ● 40 100 nA

Supply Current FB = 1.3V, Not Switching 2.8 3.6 mA

Switching Frequency (LT3461A) ● 2.1 3.0 3.9 MHz

Switching Frequency (LT3461) ● 1.0 1.3 1.7 MHz

Maximum Duty Cycle (LT3461A) ● 82 %

Maximum Duty Cycle (LT3461) ● 92 %

Switch Current Limit 300 420 600 mA

Switch V

CESAT

Switch Leakage Current VSW = 5V 0.01 1 µA

Schottky Forward Voltage I

Schottky Reverse Leakage V

SHDN Voltage High 1.5 V

SHDN Voltage Low 0.4 V

SHDN Pin Bias Current 35 50 µA

The ● denotes the specifications which apply over the full operating

SHDN

SHDN = 0V 0.1 0.5 µA

ISW = 250mA 260 350 mV

SCHOTTKY

= 250mA 800 1100 mV

– SW = 40V 0.03 4 µA

OUT

JMAX

= 150°C ON BOARD OVER

θ

JA

GROUND PLANE,

= 120°C/W

θ

JC

= 3V, unless otherwise noted.

● 1.225 1.280 V

S6 PART MARKING

LTAHG
LTAEB

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

2

Note 2: The LT3461E/LT3461AE 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.

3461af

UW

TYPICAL PERFOR A CE CHARACTERISTICS

LT3461/LT3461A

Oscillator Frequency (LT3461)

1.6

1.5

1.4

1.3

1.2

FREQUENCY (MHz)

1.1

1.0
–40 20 60

–20 0

TEMPERATURE (°C)

40 80 100

Oscillator Frequency (LT3461A)

3.9

3.6

3.3

3.0

2.7

FREQUENCY (MHz)

2.4

2.1

–60 –40

–20 0

20 60

TEMPERATURE (°C)

3461a G01

40 80 100

3461a G04

Current Limit FB Pin Voltage

480

TA = 25°C

360

240

CURRENT LIMIT (mA)

120

0

10

30

50

DUTY CYCLE (%)

Current Limit in Soft-Start Mode

480

TA = 25°C

420

360

300

240

180

CURRENT LIMIT (mA)

120

60

0

1.5 1.7 2.1

1.3
SHDN PIN VOLTAGE (V)

1.9

70

9080604020

3461a G02

2.3

3461a G05

1.28

1.27

1.26

1.25

FB VOLTAGE (V)

1.24

1.23

1.22
–40 20 60

–20 0

SHDN Pin Current

320

TA = 25°C

280

240

200

160

120

80

SHDN PIN CURRENT (µA)

40

0

0

TEMPERATURE (°C)

40 80 100

3461a G03

4812
SHDN PIN VOLTAGE (V)

3461a G06

16

V

SW

5V/DIV

V

OUT

50mV/DIV

Switching Waveform
Circuit of Figure 4

I

LOAD

= 60mA

0.2µs/DIV

3461a G08

I

LOAD

100mV/DIV

Load Transient Response
Circuit of Figure 4

70mA
35mA

V

OUT

50µs/DIV

3461a G09

3461af

3

LT3461/LT3461A

U

UU

PI FU CTIO S

SW (Pin 1): Switch Pin. Connect inductor here. Minimize
trace at this pin to reduce EMI.

GND (Pin 2): Ground Pin. Tie directly to local ground
plane.

FB (Pin 3): Feedback Pin. Reference voltage is 1.255V.
Connect resistor divider tap here. Minimize trace area at
FB. Set V

according to V

OUT

= 1.255V (1 + R1/R2).

OUT

W

BLOCK DIAGRA

6

1.255V

REFERENCE

4

SHDN

(EXTERNAL)

C

S

+

A1

–

3

FB

R

C

C

RAMP

GENERATOR

3MHz*

OSCILLATOR

V

IN

V

OUT

R1 (EXTERNAL)

FB

R2 (EXTERNAL)

(EXTERNAL)

R

SHUTDOWN

RS, CS OPTIONAL SOFT-START COMPONENTS

S

SHDN (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): Output Pin. Connect to resistor divider. Put

OUT

capacitor close to pin and close to GND plane.

V

(Pin 6): Input Supply Pin. Must be locally bypassed.

IN

1

SW

V

5

OUT

Q1

+

0.1Ω

–

GND

2

3461a F02

C

∑

COMPARATOR

–

A2

+

*LT3461 IS 1.3MHz

DRIVER

R

Q

S

Figure 1. Block Diagram

U

OPERATIO

The LT3461/LT3461A 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 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.

Layout Hints

The high speed operation of the LT3461/LT3461A de­mands careful attention to board layout. You will not get
advertised performance with careless layout. Figure 2
shows the recommended component placement.

C1

+

GND

R2

Figure 2. Suggested Layout

L1

V

IN

+

R1

C2

C3

3461a F03

V

OUT

SHUTDOWN

3461af

4

WUUU

APPLICATIO S I FOR ATIO

LT3461/LT3461A

Inrush Current

The LT3461 has a built-in Schottky diode. When supply
voltage is applied to the VIN pin, the voltage difference
between VIN and V

generates inrush current flowing

OUT

from input through the inductor and the Schottky diode to
charge the output capacitor. The maximum nonrepetitive
surge current the Schottky diode in the LT3461 can
sustain is 1.5A. The selection of inductor and capacitor
value should ensure the peak of the inrush current to be
below 1.5A. In addition, turn-on of the LT3461 should be
delayed until the inrush current is less than the maximum
current limit. The peak inrush current can be calculated as
follows:

⎞
⎟

π

⎟
⎟

L

−

⎟
⎠

C

–.

06

V

IN

I

= −

P

• exp

L

–

121

C

⎛
⎜

⎜
⎜
⎜

⎝

where L is the inductance, r is the resistance of the
inductor and C is the output capacitance.

Table 3 gives inrush peak currents for some component
selections.

Table 3. Inrush Peak Current

VIN (V) L (µH) C (µF) IP (A)

5 4.7 1 1.1

5 10 1 0.9

Thermal Considerations

Significant power dissipation can occur on the LT3461
and LT3461A, particularly at high input voltage. Device
load, voltage drops in the power path components, and
switching losses are the major contributors. It is impor­tant to measure device power dissipation in an application
to ensure that the LT3461 does not exceed the absolute
maximum operating junction temperature of 125°C over
the operating ambient temperature range. Generally, for
supply voltages below 5V the integrated current limit
function provides adequate protection for nonfault condi­tions. For supply voltages above 5V, Figures 3a and 3b
show the recommended operating region of the LT3461
and LT3461A, respectively. These graphs are based
on 250mW on-chip dissipation. Improvement of these

numbers can be expected if the LT3461 is supplied from a
separate low voltage rail.

160

VIN = 5V

VIN = 8V

14

VIN = 8V

14

VIN = 12V

VIN >15V

V

VIN = 12V

VIN >15V

V

OUT

OUT

22

22

(V)

(V)

30

30

38

3461 F01a

38

3461 F01b

120

(mA)

80

OUT

I

40

0

6

Figure 3a. LT3461 Operating Region

160

VIN = 5V

120

(mA)

80

OUT

I

40

0

6

Figure 3b. LT3461A Operating Region

Switching Frequency

The key difference between the LT3461 and LT3461A is the
faster switching frequency of the LT3461A. At 3MHz, the
LT3461A switches at twice the rate of the LT3461. The
higher switching frequency of the LT3461A allows physi­cally smaller inductors and capacitors to be used in a given
application, but with a slight decrease in efficiency and
maximum output current when compared to the LT3461.
Generally if efficiency and maximum output current are
crucial, or a high output voltage is being generated, the
LT3461 should be used. If application size and cost are
more important, the LT3461A will be the better choice.

3461af

5

LT3461/LT3461A

U

WUU

APPLICATIO S I FOR ATIO

Inductor Selection

The inductors used with the LT3461/LT3461A should
have a saturation current rating of 0.3A or greater. If the
device is used in an application where the input supply will
be hot-plugged, then the saturation current rating should
be equal to or greater than the peak inrush current. For the
LT3461, an inductor value between 10µH and 47µH,
depending upon output voltage, will usually be the best
choice for most designs. For the LT3461A, inductor values
between 4.7µH and 15µH inductor will suffice for most
applications. For best loop stability results, the inductor
value selected should provide a ripple current of 70mA or
more. For a given VIN and V
with LT3461A is estimated by the formula:

DV V

• • • sec

L (in microhenries) =

where D

VVV

=

11–

OUT IN

+

VV

OUT

+

Use twice this value for the LT3461.

the inductor value to use

OUT

IN OUT

AV

•111

have a low ESR and maintain capacitance over wide
voltage and temperature range. A 2.2µF output capacitor
is sufficient for most applications using the LT3461, while
a 1µF capacitor is sufficient for most applications using
the LT3461A. High output voltages typically require less
capacitance for loop stability. Always use a capacitor with
sufficient voltage rating.

Either ceramic or solid tantalum capacitors may be used
for the input decoupling capacitor, which should be placed
as close as possible to the LT3461/LT3461A. A 1µF
capacitor is sufficient for most applications.

Phase Lead Capacitor

A small value capacitor can be added across resistor R1
between the output and the FB pin to reduce output
perturbation due to a load step and to improve transient
response. This phase lead capacitor introduces a pole­zero pair to the feedback that boosts phase margin near
the cross-over frequency. The following formula is useful
to estimate the capacitor value needed:

Capacitor Selection

Low ESR capacitors should be used at the output to
minimize the output voltage ripple. Multilayer ceramic
capacitors using X5R/X7R dielectrics are preferred as they

U

TYPICAL APPLICATIO S

L1

47k

47nF

10µH

6

VINV

4

SHDN

1

SW

LT3461A

GND

2

OUT

V

5

R1
261k

3

FB

R2

30.1k

15pF

OUT

12V
70mA

C2
1µF

3461a TA02a

V

IN

5V

CONTROL

SIGNAL

C1

1µF

C1, C2: TAIYO YUDEN EMK212BJ105
L1: MURATA LQH32CN100K53

Figure 4. 5V to 12V with Soft-Start Circuit (LT3461A)

k

C

=

PL

Ω500

pF

R

1•

2

For an application running 50µA in the feedback divider,
capacitor values from 10pF to 22pF work well.

Input Current and Output Voltage

CONTROL

SIGNAL

5V/DIV

I

IN

50mA/DIV

V

OUT

5V/DIV

1ms/DIV

3461a TA02b

6

3461af

TYPICAL APPLICATIO S

3.3V to 5V Step-Up Converter (LT3461A)

L1

C1
1µF

OFF ON

4.7µH

6

VINV

4

SHDN

1

SW

LT3461A

GND

2

OUT

5

R1

45.3k

3

FB

R2
15k

V

IN

3.3V

C1, C2: TAIYO YUDEN X7R LMK212BJ105
L1: MURATA LQH32CN4R7M33 OR EQUIVALENT

PACKAGE DESCRIPTIO

U

U

15pF

V

OUT

5V
115mA

C2
1µF

3461a TA03a

LT3461/LT3461A

3.3V to 5V Step-Up Converter Efficiency

80

75

70

EFFICIENCY (%)

65

60

0

6030 12090

LOAD CURRENT (mA)

3461a TA03b

3.85 MAX

0.20 BSC

0.62
MAX

2.62 REF

RECOMMENDED SOLDER PAD LAYOUT

PER IPC CALCULATOR

DATUM ‘A’

0.95
REF

S6 Package

6-Lead Plastic TSOT-23

(Reference LTC DWG # 05-08-1636)

1.22 REF

1.4 MIN

2.80 BSC

1.50 – 1.75
(NOTE 4)

0.80 – 0.90

1.00 MAX

0.95 BSC

2.90 BSC
(NOTE 4)

PIN ONE ID

0.30 – 0.45
6 PLCS (NOTE 3)

0.01 – 0.10

0.30 – 0.50 REF

NOTE:

1. DIMENSIONS ARE IN MILLIMETERS

2. DRAWING NOT TO SCALE

3. DIMENSIONS ARE INCLUSIVE OF PLATING

4. DIMENSIONS ARE EXCLUSIVE OF MOLD
FLASH AND METAL BURR

5. MOLD FLASH SHALL NOT EXCEED 0.254mm

6. JEDEC PACKAGE REFERENCE IS MO-193

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.

0.09 – 0.20
(NOTE 3)

1.90 BSC

S6 TSOT-23 0302

3461af

7

LT3461/LT3461A

TYPICAL APPLICATIO S

U

Low Profile (1mm) 3.3V to 15V Step-Up Converter 3.3V to 15V Efficiency

L1

C1
1µF

OFF ON

10µH

6

VINV

4

SHDN

SW

LT3461A

GND

2

1

OUT

FB

V

IN

3.3V

C1: TAIYO YUDEN LMK107BJ105KA
C2: TAIYO YUDEN EMK316BJ225KD (X5R)
L1: MURATA LQH2MCN100K02

V

22pF

OUT

15V
25mA

C2

2.2µF

3461a TA04a

5

332k

3

30.1k

75

70

65

60

EFFICIENCY (%)

55

50

0

105203015 25

LOAD CURRENT (mA)

3461a TA04b

5V to 36V Step-Up Converter (LT3461) 5V to 36V Efficiency

L1

OFF ON

47µH

6

VINV

4

SHDN

SW

LT3461

GND

1

OUT

2

V

IN

5V

C1

1µF

C1: TAIYO YUDEN X7R LMK212BJ105
C2: MURATA GRM42-6X7R474K50
L1: MURATA LQH32CN470

V

22pF

OUT

36V
18mA

C2

0.47µF
50V

3461 TA05a

5

280k

3

FB

10k

80

75

70

65

EFFICIENCY (%)

60

55

50

0

81214624 10

LOAD CURRENT (mA)

16

3461 TA05b

3.3V to ±5V Dual Output Converter

45.3k

15k

1µF

C3

V

OUT

5V

15pF

100mA

C2
1µF

3.3V

L1

OFF ON

4.7µH

6

VINV

4

SHDN

SW

LT3461A

GND

1

5

OUT

3

FB

2

V

IN

C1

1µF

18

C1, C2, C3, C4: TAIYO YUDEN JMK107BJ105
D1, D2: PHILIPS PMEG2005EB
L1: MURATA LQH2MCN4R7M02

D1

D2

10Ω

C4
1µF

–5V
15mA

3461 TA06

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Linear Technology Corporation

8

1630 McCarthy Blvd., Milpitas, CA 95035-7417

[phone] ● FAX: [phone]

●

www.linear.com

<1µA, ThinSOT Package

SD

<1µA, MS Package

SD

I

<1µA, ThinSOT

SD

<1µA, SC70, ThinSOT Packages

I

SD

<1µA, ThinSOT Package

SD

= 34V, IQ = 20µA,

OUT(MAX)

= 34V, IQ = 20µA,

OUT(MAX)

= 5V, IQ = 19µA/300µA,

OUT(MAX)

= 36V, IQ = 2mA,

OUT(MAX)

= 34V, IQ = 1.9mA,

OUT(MAX)

3461af

LT/TP 1004 1K • PRINTED IN USA

© LINEAR TECHNOLOGY CORPORATION 2003