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

–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

0.2 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

∑

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

OPERATIO

LT3460

U

Feedback Loop Compensation

The LT3460 has an internal feedback compensation network as shown in Figure 1 (RC and CC). However, because the small signal characteristics of a boost converter change with operation conditions, the internal compensation network cannot satisfy all applications. A properly designed external feed forward capacitor from V

to FB (CF in

OUT

Figure 2) will correct the loop compensation for most applications.

L1

V

IN

5V

C1

4.7µF

OFF ON

C1: TAIYO YUDEN X5R JMK212BJ475KG C2: TAIYO YUDEN X5R EMK316BJ105 D1: CENTRAL SEMICONDUCTOR CMDSH2-3 L1: MURATA LQH32CN-220 OR EQUIVALENT

Figure 2. 5V to 12V Step-Up Converter

22µH

51

V

IN

LT3460

4

SHDN

GND

D1

SW

FB

2

R2 130k

3

R1 15k

C

F

22pF

V 12V 70mA

C2 1µF

3460 F02

OUT

is about 70kHz. The feedback loop gain T(s) = K3 • GP(s) • GC(s). If it

crosses over 0dB far before fZ, the phase margin will be small. Figure 3 is the Bode plot of the feedback loop gain measured from the converter shown in Figure 2 without the feedforward capacitor CF. The result agrees with the previous discussion: Phase margin of about 20° is insufficient.

60 50 40 30 20 10

GAIN (dB)

0 –10 –20 –30 –40

1

GAIN

PHASE

10 100 1000 FREQUENCY (kHz)

3460 F03

90 45 0 –45 –90 –135 –180 –225 –270 –315 –360

PHASE (DEG)

The LT3460 uses peak current mode control. The current feedback makes the inductor very similar to a current source in the medium frequency range. The power stage transfer function in the medium frequency range can be approximated as:

K

=

sC

•

1

,

2

G

Ps()

where C2 is the output capacitance, and K1 is a constant based on the operating point of the converter. In continuous current mode, K1 increases as the duty cycle decreases.

The internal compensation network RC, CC can be approximated as follows in medium frequency range:

GK

Cs

()

=

•

2

••

+

CC

sC

•

C

1

sR C

The zero

f

Z

=

1 RC

π

2• • •

CC

Figure 3

In order to improve the phase margin, a feed-forward capacitor CF in Figure 2 can be used.

Without the feed-forward capacitor, the transfer function from V

V

FB

OUT

to FB is:

OUT

=

R

+112

RR

With the feed-forward capacitor CF, the transfer function becomes:

V

FB

OUT

R

=

12

+

RR

1

• s

21

••

sR C

12

•

RR

•

+

12

RR

+

F

•

C

F

+

1

The feed-forward capacitor CF generates a zero and a pole. The zero always appears before the pole. The frequency distance between the zero and the pole is determined only by the ratio between V

and FB. To give maximum phase

OUT

3460f

5

LT3460

OPERATIO

U

margin, CF should be chosen so that the midpoint frequency between the zero and the pole is at the cross over frequency.

With CF = 20pF, the feedback loop Bode plot is reshaped as shown in Figure 4. The phase margin is about 60°.

3460 F04

90 45 0 –45 –90 –135 –180 –225 –270 –315 –360

PHASE (DEG)

60 50 40 30 20 10

GAIN (dB)

0 –10 –20 –30 –40

1

GAIN

PHASE

10 100 1000 FREQUENCY (kHz)

Figure 4.

The feed-forward capacitor increases the gain at high frequency. The feedback loop therefore needs to have enough attenuation at the switching frequency to reject the switching noise. Additional internal compensation components have taken this into consideration.

For most of the applications of LT3460, the output capacitor ESR zero is at very high frequency and can be ignored. If a low frequency ESR zero exists, for example, when a high-ESR Tantalum capacitor is used at the output, the phase margin may be enough even without a feed-forward capacitor. In these cases, the feed-forward capacitor should not be added because it may cause the feedback loop to not have enough attenuation at the switching frequency.

Layout Hints

The high speed operation of the LT3460 demands careful attention to board layout. You will not get advertised performance with careless layout. Figure 5 shows the recommended component placement.

D1 C1

V

OUT

+

C2

GND

L1

R2

R1

(SOT-23 PACKAGE)

+

V

IN

V

OUT

D1 C1

+

SHUTDOWN

C

F

C2

GND

L1

R2

R1

(SC70 PACKAGE)

+

V

IN

SHUTDOWN

C

F

3460 F05

Figure 5. Suggested Layout

6

3460f

U

TYPICAL APPLICATIO S

LT3460

5V to 12V Step-Up Converter

L1

V

IN

5V

C1

4.7µF

SHDN

C1: TAIYO YUDEN X5R JMK212BJ475 C2: TAIYO YUDEN X5R EMK212BJ105 D1: CENTRAL SEMICONDUCTOR CMDSH2-3 L1: MURATA LQH32CN-220 OR EQUIVALENT

22µH

51

V

IN

LT3460

4

SHDN

GND

D1

SW

FB

2

3

100mV/DIV

I

LOAD

130k

15k

V

OUT

58mA

34mA

22pF

V

OUT

12V 70mA

C2 1µF

3460 TA01

Load Step Response

90

85

80

75

EFFICIENCY (%)

70

65

60

0

Efficiency

20 40 60 80

LOAD CURRENT (mA)

3460 TA01a

5V to 12V with Soft-Start Circuit

L1

V

SHDN

IN

22µH

SW

LT3460

GND

V

IN

5V

C1

4.7µF

C1: TAIYO YUDEN X5R JMK212BJ475 C2: TAIYO YUDEN X5R EMK212BJ105 D1: CENTRAL SEMICONDUCTOR CMDSH2-3 L1: MURATA LQH32CN-220 OR EQUIVALENT

CONTROL

SIGNAL

47k

47nF

100µs/DIV

3460 TA01b

Input Current and Output Voltage

D1

130k

FB

15k

22pF

V

OUT

12V 70mA

C2 1µF 16V

3460 TA02

I

100mA/DIV

V

5V/DIV

CONTROL

SIGNAL

2V/DIV

IN

O

500µs/DIV

3460 TA02b

3460f

7

LT3460

LOAD CURRENT (mA)

010

20 30 40

EFFICIENCY (%)

3460 TA03a

85

80

75

70

65

60

55

U

TYPICAL APPLICATIO S

3.3V to 12V Step-Up Converter

L1

V

SHDN

22µH

IN

LT3460

GND

V

IN

3.3V

C1

4.7µF

C1: TAIYO YUDEN X5R JMK212BJ475 C2: TAIYO YUDEN X5R EMK212BJ105 D1: CENTRAL SEMICONDUCTOR CMDSH2-3 L1: MURATA LQH32CN-220 OR EQUIVALENT

D1

SW

FB

Li-Ion to 5V Step-Up Converter

L1

V

IN

SHDN

10µH

LT3460

GND

V

IN

2.7V TO

4.2V

+

C1

4.7µF

C1: TAIYO YUDEN X5R JMK212BJ475 C2: TAIYO YUDEN X5R JMK212BJ475 D1: PHILIPS PMEG2010 L1: MURATA LQH32CN-100 OR EQUIVALENT

D1

SW

FB

130k

15k

39.2k

13k

22pF

50pF

V

OUT

12V 40mA

C2 1µF 16V

3460 TA03

V

OUT

5V

C2

4.7µF

6.3V

3460 TA07

90 88 86 84 82 80 78

EFFICIENCY (%)

76 74 72 70

0

Efficiency

VIN = 2.7V

50 100

LOAD CURRENT (mA)

VIN = 3.6V

VIN = 3V

150

VIN = 4.2V

200 250

3460 TA07a

8

3460f

U

TYPICAL APPLICATIO S

12V to 36V Step-Up Converter

L1

V

IN

SHDN

47µH

SW

LT3460

FB

GND

V

IN

12V

C1

1µF

16V

C1: TAIYO YUDEN X5R EMK212BJ105 C2: TAIYO YUDEN X7R UMK212BJ224 D1, D2: CENTRAL SEMICONDUCTOR CMOD4448 L1: TAIYO YUDEN LB2012

D1

D2

278k

10k

22pF

V

OUT

36V 4mA

C2

0.22µF 50V

3460 TA04

V

OUT

100mV/DIV

4mA

I

LOAD

2mA

Load Step Response

100µs/DIV

LT3460

3460 TA04a

5V to 36V Step-Up Converter

L1

V

IN

SHDN

47µH

SW

LT3460

FB

GND

V

IN

5V

C1

1µF

6.3V

C1: TAIYO YUDEN X5R JMK107BJ105 C2: TAIYO YUDEN X7R UMK212BJ224 D1, D2: CENTRAL SEMICONDUCTOR CMOD4448 L1: TAIYO YUDEN LB2012

D1

D2

278k

10k

22pF

V

OUT

36V 4mA

C2

0.22µF 50V

3460 TA05

V

OUT

100mV/DIV

4mA

I

LOAD

2mA

Load Step Response

100µs/DIV

3460 TA05a

3460f

9

LT3460

PACKAGE DESCRIPTIO

U

S5 Package

5-Lead Plastic TSOT-23

(Reference LTC DWG # 05-08-1635)

0.62 MAX

3.85 MAX

0.20 BSC

DATUM ‘A’

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

2.62 REF

RECOMMENDED SOLDER PAD LAYOUT

PER IPC CALCULATOR

0.30 – 0.50 REF

0.95 REF

1.22 REF

1.4 MIN

0.09 – 0.20 (NOTE 3)

2.80 BSC

1.50 – 1.75 (NOTE 4)

1.00 MAX

PIN ONE

0.95 BSC

0.80 – 0.90

2.90 BSC (NOTE 4)

0.30 – 0.45 TYP 5 PLCS (NOTE 3)

0.01 – 0.10

1.90 BSC

S5 TSOT-23 0302

10

3460f

PACKAGE DESCRIPTIO

LT3460

U

SC6 Package

6-Lead Plastic SC70

(Reference LTC DWG # 05-08-1638)

0.47

MAX

3.26 MAX

2.1 REF

RECOMMENDED SOLDER PAD LAYOUT

PER IPC CALCULATOR

0.10 – 0.40

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. DETAILS OF THE PIN 1 INDENTIFIER ARE OPTIONAL, BUT MUST BE LOCATED WITHIN THE INDEX AREA

7. EIAJ PACKAGE REFERENCE IS EIAJ SC-70

0.65 REF

1.16 REF

0.96 MIN

0.10 – 0.30

1.80 – 2.40

0.10 – 0.18 (NOTE 3)

1.15 – 1.35 (NOTE 4)

1.00 MAX

PIN 1

0.65 BSC

0.80 – 1.00

1.80 – 2.20 (NOTE 4)

INDEX AREA (NOTE 6)

0.15 – 0.30 6 PLCS (NOTE 3)

0.00 – 0.10 REF

SC6 SC70 0802

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.

3460f

11

LT3460

LOAD CURRENT (mA)

050

100 150

EFFICIENCY (%)

3460 TA06a

80

75

70

65

60

55

50

VIN = 4V

VIN = 5V

VIN = 6.5V

TYPICAL APPLICATIO S

5V to 5V SEPIC Efficiency

SW

C3

0.22µF

FB

D1

L2 22µH

V

3V TO 10V

1µF

L1

V

IN

SHDN

22µH

LT3460

IN

C1

U

30k

50pF

V 5V 50mA

C2 1µF

OUT

GND

C1, C2: TAIYO YUDEN X5R LMK107BJ105 C3: TAIYO YUDEN X7R LMK107BJ224 D1: ON SEMICONDUCTOR MBR0520 L1, L2: MURATA LQH32CN-220 OR EQUIVALENT

10k

3460 TA06

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OUT(MAX)

= 35V, IQ = 0.9mA, I

OUT(MAX)

= 6V, IQ = 38µA, I

OUT(MAX)

= 34V, IQ = 3mA, I

= 34V, IQ = 20µA, I

= ±34V, IQ = 20µA, I

SD

<1µA,

<6µA,

= 5V, IQ = 19µA/300µA, I

<1µA, MS Package

SD

= 38V, IQ = 2.8mA, I

= 34V, IQ = 25µA, I

= 30V, IQ = 1.9mA, I

SD

<1µA,

SD

<1µA,

SD

<1µA,

12

Linear Technology Corporation

1630 McCarthy Blvd., Milpitas, CA 95035-7417

(408) 432-1900 ● FAX: (408) 434-0507

●

www.linear.com

3460f

LT/TP 0204 1K • PRINTED IN USA

 LINEAR TECHNO LOGY CORPO R ATIO N 2003

LINEAR TECHNOLOGY LT3460 Technical data

Specifications and Main Features

Frequently Asked Questions

User Manual