LT1946_技术文档

LT1946

1.2MHz Boost

DC/DC Converter with

1.5A Switch and Soft-Start

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FEATURES

DESCRIPTIO

TheLT^®1946isafixedfrequencystep-upDC/DCconverter

containing an internal 1.5A, 36V switch. Capable of gener-

ating 8V at 430mA from a 3.3V input, the LT1946 is ideal

for large TFT-LCD panel power supplies. The LT1946

switches at 1.2MHz, allowing the use of tiny, low profile

inductors and low value ceramic capacitors. Loop com-

pensationcanbeeitherinternalorexternal, givingtheuser

flexibility in setting loop compensation and allowing opti-

mized transient response with low ESR ceramic output

capacitors.Soft-startiscontrolledwithanexternalcapaci-

tor, which determines the input current ramp rate during

start-up.

■

1.5A, 36V Internal Switch

■

1.2MHz Switching Frequency

■

Integrated Soft-Start Function

Output Voltage Up to 34V

Low V_CESATSwitch: 300mV at 1.5A (Typ)

8V at 430mA from a 3.3V Input

Small 8-Lead MSOP Package

■

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APPLICATIO S

■

TFT-LCD Bias Supplies

■

GPS Receivers

■

DSL Modems

Local Power Supplies

The 8-lead MSOP package and high switching frequency

ensurealowprofileoverallsolutionlessthan1.2mmhigh.

■

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

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TYPICAL APPLICATIO

Efficiency

L1

D1

90

85

80

75

4.7µH

V

OUT

V

IN

8V

3.3V

430mA

6

5

SW

V

R1

28.7k

IN

3

1

OFF ON

SHDN

C1

LT1946

2

2.2µF

C2

20µF

70

65

V

C

FB

R

C

SS COMP GND

49.9k

R2

5.23k

8

7

4

C

SS

60

55

50

470pF

100nF

1946 F01

C1: 2.2µF, X5R OR X7R, 6.3V

C2: 2 × 10µF, X5R OR X7R, 10V

D1: MICROSEMI UPS120 OR EQUIVALENT

L1: TDK RLF5018T-4R7M1R4

100

200

LOAD CURRENT (mA)

400

0

500

300

1946 F01b

Figure 1. 3.3V to 8V, 430mA Step-Up DC/DC Converter

sn1946 1946fs

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LT1946

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ABSOLUTE AXI U RATI GS

PACKAGE/ORDER I FOR ATIO

(Note 1)

ORDER PART

V_INVoltage ............................................................. 16V

SW Voltage ............................................... –0.4V to 36V

FB Voltage ............................................................. 2.5V

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

Current Into FB Pin .............................................. ±1mA

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

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

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

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

NUMBER

TOP VIEW

V

1

2

3

4

8 SS

7 COMP

C

LT1946EMS8

FB

SHDN

GND

6 V

5 SW

IN

MS8 PACKAGE

8-LEAD PLASTIC MSOP

MS8 PART MARKING

LTUG

T_JMAX= 125°C, θ_JA= 125°C/W

(4-LAYER BOARD)

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

ELECTRICAL CHARACTERISTICS

The ● denotes the specifications which apply over the full operating

temperature range, otherwise specifications are at T_A= 25°C. V_IN= 3V, V_SHDN= V_INunless otherwise specified. (Note 2)

SYMBOL

CONDITIONS

MIN

TYP

MAX

2.6

UNITS

Minimum Operating Voltage

Maximum Operating Voltage

Feedback Voltage

2.45

V

16

1.230

1.220

1.250

1.270

V

●

FB Pin Bias Current

V

FB

= 1.250V (Note 3)

20

40

120

nA

µmhos

V/V

Error Amp Transconductance

Error Amp Voltage Gain

Quiescent Current

∆I = 2µA

300

3.2

0

V

= 2.5V, Not Switching

5

1

mA

SHDN

Quiescent Current in Shutdown

Reference Line Regulation

Switching Frequency

= 0V, V = 3V

µA

SHDN

IN

2.6V ≤ V ≤ 16V

0.01

1.2

0.05

%/V

IN

0.9

0.8

1.4

1.5

MHz

●

Switching Frequency in Foldback

Maximum Duty Cycle

V

= 0V

0.4

90

MHz

%

FB

●

86

Switch Current Limit

(Note 4)

= 1A

1.5

2.1

240

0.01

4

3.1

340

1

A

Switch V

I

mV

µA

V

CESAT

SW

Switch Leakage Current

Soft-Start Charging Current

SHDN Input Voltage High

SHDN Input Voltage Low

SHDN Pin Bias Current

V

SW

V

SS

= 5V

= 0.5V

2.5

2.4

6

0.5

V

SHDN

V

SHDN

= 3V

= 0V

16

0

32

0.1

µA

Note 1: Absolute Maximum Ratings are those values beyond which the life

Note 3: Current flows out of FB pin.

of a device may be impaired.

Note 4: Current limit guaranteed by design and/or correlation to static test.

Note 2: The LT1946E is guaranteed to meet performance 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.

Current limit is independent of duty cycle and is guaranteed by design.

sn1946 1946fs

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LT1946

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TYPICAL PERFOR A CE CHARACTERISTICS

Feedback Pin Voltage

Oscillator Frequency

Current Limit

2.6

2.4

2.2

2.0

1.8

1.6

1.4

1.2

1.0

0.8

0.6

0.4

0.2

0

1400

1200

1000

800

600

400

200

0

1.28

1.27

1.26

T

= –30°C

T

= 100°C

= 25°C

1.25

1.24

1.23

1.22

1.21

A

1.20

–50 –25

0

25

50

75 100 125

–25

0

50

75 100 125

0.8

1.2

–50

25

0

0.2

0.4

0.6

1.0

TEMPERATURE (°C)

FEEDBACK VOLTAGE (V)

1946 G03

1946 G01

1946 G02

Switching Waveforms

for Figure 1 Circuit

Switch Saturation Voltage

Quiescent Current

3.8

3.6

3.4

3.2

3.0

2.8

2.6

2.4

2.2

0.35

0.30

V_OUT

20mV/DIV

AC COUPLED

0.25

V_SW

5V/DIV

0.20

0.15

0.10

0.05

0V

I_LI

0.5A/DIV

AC COUPLED

0.5µs/DIV

1946 G06

2.0

0

–50 –25

0

25

50

125

75 100

0

0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6

TEMPERATURE (°C)

SWITCH CURRENT (A)

1946 G05

1946 G04

sn1946 1946fs

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LT1946

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PI FU CTIO S

V_C(Pin 1): Error Amplifier Output Pin. Tie external com-

pensation network to this pin, or use the internal compen-

sation network by shorting the V_Cpin to the COMP pin.

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

COMP (Pin 7): Internal Compensation Pin. Provides an

internal compensation network. Tie directly to the V_Cpin

for internal compensation. Tie to GND if not used.

FB (Pin 2): Feedback Pin. Reference voltage is 1.250V.

Connect resistive divider tap here. Minimize trace area at

FB. Set V_OUTaccording to V_OUT= 1.250(1 + R1/R2).

SS (Pin 8): Soft-Start Pin. Place a soft-start capacitor

here. Upon start-up, 4µA of current charges the capacitor

to 1.5V. Use a larger capacitor for slower start-up. Leave

floating if not in use.

SHDN(Pin3):ShutdownPin.Tieto2.4Vormoretoenable

device. Ground to shut down. Do not float this pin.

GND (Pin 4): Ground. Tie directly to local ground plane.

SW (Pin 5): Switch Pin. This is the collector of the internal

NPN power switch. Minimize the metal trace area con-

nected to this pin to minimize EMI.

W

BLOCK DIAGRA

SS

8

V

COMP

C

1

7

120k

90pF

4µA

SW

5

COMPARATOR

–

+

DRIVER

R

Q

A2

Q1

S

V

IN

1.250V

REFERENCE

6

+

–

+

–

0.01Ω

A1

Σ

V

OUT

RAMP

GENERATOR

R1 (EXTERNAL)

FB

4

0.5V

+

–

GND

R2 (EXTERNAL)

÷3

1946 BD

1.2MHz

OSCILLATOR

A3

SHUTDOWN

3

2

SHDN

FB

Figure 2. Block Diagram

sn1946 1946fs

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LT1946

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OPERATIO

The LT1946 uses a constant frequency, current mode

control scheme to provide excellent line and load regula-

tion. Please refer to Figure 2 for the following description

of the part’s operation. At the start of the oscillator cycle,

the SR latch is set, turning on the power switch Q1. The

switch current flows through the internal current sense

resistor generating a voltage. This voltage is added to a

stabilizing ramp and the resulting sum is fed into the

positive terminal of the PWM comparator A2. When this

voltageexceedsthelevelatthenegativeinputofA2,theSR

latch is reset, turning off the power switch. The level at the

negative input of A2 (V_Cpin) 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

1.250V. In this manner, the error amplifier sets the correct

peak current level to keep the output in regulation.

below a nominal value of 0.5V. This is accomplished via

comparator A3. This feature reduces the minimum duty

cycle that the part can achieve thus allowing better control

of the switch current during start-up. When the FB pin

voltage exceeds 0.5V, the oscillator returns to the normal

frequencyof1.2MHz.Asoft-startfunctionisalsoprovided

by the LT1946. When the part is brought out of shutdown,

4µA of current is sourced out of the SS pin. By connecting

an external capacitor to the SS pin, the rate of voltage rise

on the pin can be set. Typical values for the soft-start

capacitor range from 10nF to 200nF. The SS pin directly

limits the rate of rise on the V_Cpin, which in turn limits the

peak switch current. Current limit is not shown in Figure 2.

The switch current is constantly monitored and not al-

lowed to exceed the nominal value of 2.1A. If the switch

current reaches 2.1A, the SR latch is reset regardless of

the output of comparator A2. This current limit helps

protect the power switch as well as the external compo-

nents connected to the LT1946.

Two functions are provided to enable a very clean start-up

for the LT1946. Frequency foldback is used to reduce the

oscillator frequency by a factor of 3 when the FB pin is

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APPLICATIO S I FOR ATIO

TheinductorsshowninTable1werechosenforsmallsize.

For better efficiency, use similar valued inductors with a

larger volume.

Inductor Selection

SeveralinductorsthatworkwellwiththeLT1946arelisted

in Table 1. This table is not exclusive; there are many other

manufacturers and inductors that can be used. Consult

each manufacturer for more detailed information and for

their entire selection of related parts, as many different

sizes and shapes are available. Ferrite core inductors

shouldbeusedtoobtainthebestefficiency, ascorelosses

at 1.2MHz are much lower for ferrite cores than for the

cheaperpowdered-ironones. Chooseaninductorthatcan

handleatleast1.5Awithoutsaturating,andensurethatthe

inductor has a low DCR (copper wire resistance) to mini-

mize I²R power losses. A 4.7µH to 10µH inductor will be

the best choice for most LT1946 designs. Note that in

some applications, the current handling requirements of

the inductor can be lower, such as in the SEPIC topology

where each inductor only carries one-half of the total

switch current.

Table 1. Recommended Inductors

MAX

DCR

(µH) (mΩ)

SIZE

L × W × H

(mm)

L

PART

VENDOR

CDRH5D18-4R1

CDRH5D18-5R4

CDRH5D28-5R3

CDRH5D28-6R2

CDRH5D28-8R2

4.1

5.4

5.3

6.2

8.2

57

76

38

45

53

5.7 × 5.7 × 2

Sumida

(847) 956-0666

www.sumida.com

5.7 × 5.7 × 3

ELL6SH-4R7M

ELL6SH-5R6M

ELL6SH-6R8M

4.7

5.6

6.8

50

59

62

6.4 × 6 × 3

Panasonic

(408) 945-5660

www.panasonic.com

RLF5018T-

4R7M1R4

4.7

45

5.6 × 5.2 × 1.8 TDK

(847) 803-6100

www.tdk.com

sn1946 1946fs

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LT1946

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APPLICATIO S I FOR ATIO

Capacitor Selection

Low ESR (equivalent series resistance) capacitors should

beusedattheoutputtominimizetheoutputripplevoltage.

Multilayer ceramic capacitors are an excellent choice, as

they have an extremely low ESR and are available in very

small packages. X5R dielectrics are preferred, followed by

X7R, as these materials retain the capacitance over wide

voltage and temperature ranges. A 4.7µF to 20µF output

capacitor is sufficient for most applications, but systems

withverylowoutputcurrentsmayneedonlya1µFor2.2µF

output capacitor. Solid tantalum or OS-CON capacitors

can be used, but they will occupy more board area than a

ceramicandwillhaveahigherESR.Alwaysuseacapacitor

with a sufficient voltage rating.

V_OUT

20mV/DIV

AC COUPLED

I_LI

0.5A/DIV

AC COUPLED

R

_C= 7.5k

200µs/DIV

1946 F03a

Figure 3a. Transient Response Shows Excessive Ringing

V_OUT

20mV/DIV

Ceramic capacitors also make a good choice for the input

decoupling capacitor, which should be placed as close as

possible to the LT1946. A 2.2µF to 4.7µF input capacitor is

sufficient for most applications. Table 2 shows a list of

several ceramic capacitor manufacturers. Consult the

manufacturers for detailed information on their entire

selection of ceramic parts.

AC COUPLED

I_LI

0.5A/DIV

AC COUPLED

R_C= 18k

200µs/DIV

1946 F03b

Figure 3b. Transient Response is Better

Table 2. Ceramic Capacitor Manufacturers

Taiyo Yuden

(408) 573-4150

www.t-yuden.com

AVX

(803) 448-9411

www.avxcorp.com

Murata

(714) 852-2001

www.murata.com

V_OUT

20mV/DIV

AC COUPLED

Compensation—Adjustment

I_LI

0.5A/DIV

To compensate the feedback loop of the LT1946, a series

resistor-capacitor network should be connected from the

COMP pin to GND. For most applications, a capacitor in

the range of 220pF to 680pF will suffice. A good starting

value for the compensation capacitor, C_C, is 470pF. The

compensation resistor, R_C, is usually in the range of 20k

to 100k. A good technique to compensate a new applica-

tion is to use a 100kΩ potentiometer in place of R_C, and

use a 470pF capacitor for C_C. By adjusting the potentiom-

eter while observing the transient response, the optimum

value for R_Ccan be found. Figures 3a to 3c illustrate this

process for the circuit of Figure 1 with a load current

steppedfrom250mAto300mA.Figure3ashowsthetran-

sient response with R_Cequal to 7.5k. The phase margin is

AC COUPLED

R_C= 49.9k

200µs/DIV

1946 F03b

Figure 3c. Transient Response is Well Damped

poor as evidenced by the excessive ringing in the output

voltage and inductor current. In Figure 3b, the value of R_C

is increased to 18k, which results in a more damped re-

sponse. Figure 3c shows the results when R_Cis increased

further to 49.9k. The transient response is nicely damped

and the compensation procedure is complete. The COMP

pin provides access to an internal resistor (120k) and

capacitor (90pF). For some applications, these values will

suffice and no external R_Cand C_Cwill be needed.

sn1946 1946fs

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LT1946

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APPLICATIO S I FOR ATIO

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Compensation—Theory

–

+

Like all other current mode switching regulators, the

LT1946 needs to be compensated for stable and efficient

operation. Two feedback loops are used in the LT1946: a

fast current loop which does not require compensation,

and a slower voltage loop which does. Standard Bode plot

analysis can be used to understand and adjust the voltage

feedback loop.

g

mp

V

OUT

C

R

L

OUT

1.250V

REFERENCE

+

–

V

C

g

ma

R1

R

C

R

O

R2

1946 F04

C

C : COMPENSATION CAPACITOR

C

As with any feedback loop, identifying the gain and phase

contribution of the various elements in the loop is critical.

Figure 4 shows the key equivalent elements of a boost

converter. Because of the fast current control loop, the

power stage of the IC, inductor and diode have been

replaced by the equivalent transconductance amplifier

C

g

mp

: OUTPUT CAPACITOR

OUT

: TRANSCONDUCTANCE AMPLIFIER INSIDE IC

ma

g

: POWER STAGE TRANSCONDUCTANCE AMPLIFIER

R : COMPENSATION RESISTOR

C

L

O

R : OUTPUT RESISTANCE DEFINED AS V

DIVIDED BY I

LOAD(MAX)

OUT

R : OUTPUT RESISTANCE OF g

ma

R1, R2: FEEDBACK RESISTOR DIVIDER NETWORK

Figure 4. Boost Converter Equivalent Model

g

_mp. g_mpactsasacurrentsourcewheretheoutputcurrent

is proportional to the V_Cvoltage. Note that the maximum

output current of g_mpis finite due to the current limit in the

IC.

The Current Mode zero is a right half plane zero which can

be an issue in feedback control design, but is manageable

with proper external component selection.

From Figure 4, the DC gain, poles and zeroes can be

calculated as follows:

Using the circuit of Figure 1 as an example, the following

tableshowstheparametersusedtogeneratetheBodeplot

shown in Figure 5.

Table 3. Bode Plot Parameters

2

Output Pole: P1=

Parameter

Value

18.6

20

Units

Ω

Comment

2• π •R_L•C_OUT

R

L

Application Specific

Not Adjustable

Adjustable

1

Error Amp Pole: P2 =

2• π •R_O•C_C

1

Error Amp Zero: Z1=

2• π •R_C•C_C

C

OUT

µF

R

C

R

10

MΩ

pF

O

C

470

49.9

8

kΩ

V

Adjustable

V

OUT

Application Specific

Not Adjustable

Application Specific

Not Adjustable

1.25

V_OUT

DC GAIN: A =

•g_ma•R_O•g_mp•R_L

V

3.3

40

V

IN

g

µmho

mho

µH

ma

1

ESR Zero: Z2 =

5

mp

2• π •ESR•C_OUT

L

5.4

1.2

V

²•R_L

f

MHz

IN

S

RHP Zero: Z3 =

2• π •V_OUT²•L

From Figure 5, the phase is 120° when the gain reaches

0dB giving a phase margin of 60°. This is more than

adequate. The crossover frequency is 25kHz, which is

aboutthreetimeslowerthanthefrequencyoftherighthalf

plane zero Z2. It is important that the crossover frequency

be at least three times lower than the frequency of the RHP

f_S

3

High Frequency Pole: P3 >

zero to achieve adequate phase margin.

sn1946 1946fs

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LT1946

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APPLICATIO S I FOR ATIO

100

Diode Selection

ASchottkydiodeisrecommendedforusewiththeLT1946.

The Microsemi UPS120 is a very good choice. Where the

input to output voltage differential exceeds 20V, use the

UPS140(a40Vdiode).Thesediodesareratedtohandlean

average forward current of 1A. For applications where the

average forward current of the diode is less than 0.5A, an

ON Semiconductor MBR0520 diode can be used

50

0

–50

Setting Output Voltage

100

1k

10k 25k 100k

FREQUENCY (Hz)

1M

To set the output voltage, select the values of R1 and R2

(see Figure 1) according to the following equation:

1946 F05a

0

V_OUT

1.25V

R1= R2

– 1

A good range for R2 is from 5k to 30k.

–100

Layout Hints

60°

ThehighspeedoperationoftheLT1946demandscareful

attention to board layout. You will not get advertised

performance with careless layout. Figure 6 shows the

recommended component placement for a boost

converter.

–180

–200

100

1k

10k 25k 100k

FREQUENCY (Hz)

1M

1946 F05b

Figure 5. Bode Plot of Figure 1’s Circuit

GROUND PLANE

C

SS

C1

+

C

V

IN

R

1

8

7

6

5

R1

2

3

4

L1

LT1946

R2

SHUTDOWN

MULTIPLE

VIAs

C2

GND

V

OUT

1946 F06

Figure 6. Recommended Component Placement for Boost Converter. Note Direct High Current Paths Using Wide PC Traces. Minimize

Trace Area at Pin 1 (V_C) and Pin 2 (FB). Use Multiple Vias to Tie Pin 4 Copper to Ground Plane. Use Vias at One Location Only to Avoid

Introducing Switching Currents Into the Ground Plane

sn1946 1946fs

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LT1946

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TYPICAL APPLICATIO S

Low Profile, Triple Output TFT Supply (10V, –10V, 20V)

D2

D3

V

ON

20V

5mA

C5

0.1µF

L1

5.4µH

AV

D1

DD

V

10V

IN

3.3V TO 5V

450mA, V = 5V

IN

6

5

SW

275mA, V = 3.3V

IN

R1

V

IN

3

8

7

75k

OFF ON

SHDN

SS LT1946

COMP

2

+

C2

20µF

C3

1µF

FB

C1

4.7µF

V

GND

4

C

1

R

33.3k

R2

10.5k

C

SS

C

100nF

C

470pF

C6

0.1µF

C1 TO C6: X5R OR X7R

C1: 4.7µF, 6.3V

C2: 2 × 10µF, 10V

C3: 1µF, 25V

C4: 2.2µF, 10V

C5, C6: 0.1µF, 10V

D4

D5

C4

2.2µF

V

OFF

D1: MICROSEMI UPS120 OR EQUIVALENT

D2 TO D5: ZETEX BAT54S OR EQUIVALENT

L1: SUMIDA CDRH5D18-5R4

–10V

1946 TA01

10mA

Efficiency

Transient Response

90

85

80

75

AV_DD

V

= 5V

IN

50mV/DIV

AC COUPLED

V

= 3.3V

IN

I_LI

0.5A/DIV

70

65

60

55

50

AV_DD

150mA

LOAD 100mA

V

LOAD = 5mA

LOAD = 10mA

ON

OFF

V

_IN= 5V

100µs/DIV

1946 TA01b

100

200

400

0

500

300

AV LOAD CURRENT (mA)

DD

1946 TA01a

sn1946 1946fs

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LT1946

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TYPICAL APPLICATIO S

12V Output Boost Converter

L1

D1

V

OUT

4.7µH

V

12V

410mA, V = 5V

IN

3.3V TO 5V

IN

6

5

SW

275mA, V = 3.3V

V

IN

R1

84.5k

3

1

OFF ON

SHDN

C1

LT1946

2

4.7µF

C2

4.7µF

V

FB

C

R

C

SS COMP GND

33.3k

R2

9.76k

8

7

4

C

SS

470pF

100nF

1946 TA02

C1: 4.7µF, X5R OR X7R, 6.3V

C2: 4.7µF, X5R OR X7R, 16V

D1: MICROSEMI UPS120 OR EQUIVALENT

L1: TDK RLF5018T-4R7M1R4

Efficiency

Transient Response

90

85

80

75

V

= 5V

IN

V_OUT

100mV/DIV

V

= 3.3V

AC COUPLED

IN

70

65

I_LI

0.5A/DIV

60

55

50

175mA

100mA

I_LOAD

V

_IN= 3.3V

100µs/DIV

1946 TA02b

100

200

300

400

0

500

LOAD CURRENT (mA)

1946 TA02a

sn1946 1946fs

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LT1946

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PACKAGE DESCRIPTIO

MS8 Package

8-Lead Plastic MSOP

(Reference LTC DWG # 05-08-1660)

0.889 ± 0.127

(.035 ± .005)

5.23

(.206)

MIN

3.2 – 3.45

(.126 – .136)

3.00 ± 0.102

(.118 ± .004)

(NOTE 3)

0.52

(.206)

REF

0.65

(.0256)

BSC

0.42 ± 0.04

(.0165 ± .0015)

TYP

8

7 6

5

RECOMMENDED SOLDER PAD LAYOUT

3.00 ± 0.102

(.118 ± .004)

NOTE 4

4.88 ± 0.1

(.192 ± .004)

DETAIL “A”

0.254

(.010)

0° – 6° TYP

GAUGE PLANE

1

2

3

4

0.53 ± 0.015

(.021 ± .006)

1.10

(.043)

MAX

0.86

(.034)

REF

DETAIL “A”

0.18

(.077)

SEATING

PLANE

0.22 – 0.38

(.009 – .015)

0.13 ± 0.05

(.005 ± .002)

0.65

(.0256)

BCS

MSOP (MS8) 1001

NOTE:

1. DIMENSIONS IN MILLIMETER/(INCH)

2. DRAWING NOT TO SCALE

3. DIMENSION DOES NOT INCLUDE MOLD FLASH, PROTRUSIONS OR GATE BURRS.

MOLD FLASH, PROTRUSIONS OR GATE BURRS SHALL NOT EXCEED 0.152mm (.006") PER SIDE

4. DIMENSION DOES NOT INCLUDE INTERLEAD FLASH OR PROTRUSIONS.

INTERLEAD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.152mm (.006") PER SIDE

5. LEAD COPLANARITY (BOTTOM OF LEADS AFTER FORMING) SHALL BE 0.102mm (.004") MAX

sn1946 1946fs

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 represen-

tationthattheinterconnectionofitscircuitsasdescribedhereinwillnotinfringeonexistingpatentrights.

11

LT1946

U

TYPICAL APPLICATIO

Low Profile, Triple Output TFT Supply (8V, –8V, 23V)

D2

D3

D4

D5

V

ON

23V

5mA

C5

0.1µF

C6

0.1µF

C7

0.1µF

L1

5.4µH

D1

AV

8V

DD

V

IN

3.3V

375mA

6

5

V

SW

R2

28.7k

IN

SHDN

3

8

7

OFF ON

SS LT1946

COMP

2

+

C2

20µF

C4

1µF

FB

C1

4.7µF

V

GND

4

C

1

R

49.9k

R3

5.23k

C

SS

100nF

C

470pF

C8

0.1µF

C1 TO C8: X5R OR X7R

C1: 4.7µF, 6.3V

D7

D6

C3

2.2µF

C2: 2 × 10µF, 10V

C3: 2.2µF, 10V

C4: 1µF, 25V

C5, C6, C8: 0.1µF, 10V

C7: 0.1µF, 16V

V

OFF

–8V

D1: MICROSEMI UPS120 OR EQUIVALENT

D2 TO D5: ZETEX BAT54S OR EQUIVALENT

L1: SUMIDA CDRH5D18-5R4

1946 TA03

10mA

Efficiency

Start-Up Waveforms

85

80

75

AV_DD

2V/DIV

V_ON

70

65

60

55

50

10V/DIV

V_OFF

5V/DIV

V

LOAD = 5mA

ON

OFF

I_IN

200mA/V

LOAD = 10mA

0

100

200

300

400

1ms/DIV

1946 TA04

AV LOAD CURRENT (mA)

DD

1946 TA03a

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COMMENTS

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V

= 1.2V to 15V, V

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IN

OUT

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LT1946A

LT1947

Dual ±250mA Boost Converter

to ±34V, MS10 Package

12.7MHz, 1.5A Boost DC/DC Converter

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= 2.45V to 16V, V

to 34V, MS8E Package

OUT

8V at 200mA from 3.3V Input, 10-Lead MSOP Package

Burst Mode and ThinSOT are trademarks of Linear Technology Corporation.

sn1946 1946fs

LT/TP 1002 2K • PRINTED IN USA

12 ^{LinearTechnology Corporation}

1630 McCarthy Blvd., Milpitas, CA 95035-7417

●

(408) 432-1900 FAX: (408) 434-0507 www.linear.com

LINEAR TECHNOLOGY CORPORATION 2001


型号：	LT1946
厂家：	Linear
描述：	1.2MHz Boost DC/DC Converter with 1.5A Switch and Soft-Start 的1.2MHz升压型DC / DC转换器与1.5A开关和软启动转换器开关软启动
文件：	总12页 (文件大小：268K)
中文：	中文翻译
下载：	下载PDF数据表文档文件

LT1946 [Linear]

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