LT1946A_技术文档

LT1946A

2.7MHz Boost DC/DC

Converter with 1.5A Switch

and Soft-Start

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FEATURES

DESCRIPTIO

■

1.5A, 36V Internal Switch

The LT^®1946A is a fixed frequency step-up DC/DC con-

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

generating 12V at 430mA from a 5V input, the LT1946A is

ideal for powering large TFT-LCD panels. The LT1946A

switches at 2.7MHz, 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. The 8-lead MSOP package and high switching

frequency ensure a low profile overall solution less than

1.1mm high.

■

2.7MHz Switching Frequency

■

Integrated Soft-Start Function

Adjustable Output from V_INto 35V

■

Low V_CESATSwitch: 300mV at 1.5A (Typical)

■

12V at 430mA from a 5V Input

■

Small Thermally Enhanced 8-Lead MSOP Package

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APPLICATIO S

■

TFT-LCD Bias Supplies

■

GPS Receivers

■

DSL Modems

Local Power Supply

■

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

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TYPICAL APPLICATIO

L1

D1

Efficiency

2.2µH

V

OUT

V

IN

12V

90

5V

430mA

6

5

SW

R1

85

80

75

70

65

60

55

50

V

IN

182k

3

1

OFF ON

SHDN

LT1946A

2

7

C1

FB

2.2µF

C2

2.2µF

V

C

COMP

GND*

4

R

C

SS

27.4k

R2

21k

8

C

SS

100nF

270pF

1946A TA01

C1: 2.2µF, X5R or X7R, 6.3V

C2: 2.2µF, X5R or X7R, 16V

D1: MICROSEMI UPS120 OR EQUIVALENT

L1: SUMIDA CR43-2R2

* EXPOSED PAD MUST ALSO BE GROUNDED

0

100

200

300

400

500

LOAD CURRENT (mA)

Figure 1. 5V to 12V, 430mA Step-Up DC/DC Converter

1946A TA01

sn1946a 1946afs

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LT1946A

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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

Current into FB Pin ............................................... ±1mA

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

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

TOP VIEW

NUMBER

V

1

2

3

4

8 SS

7 COMP

C

FB

SHDN

GND

LT1946AEMS8E

6 V

5 SW

IN

MS8E PACKAGE

8-LEAD PLASTIC MSOP

EXPOSED PAD IS GROUND

(MUST BE SOLDERED TO PCB)

MS8E PART

MARKING

LTYZ

T_JMAX= 125°C, θ_JA= 40°C/W,

θ_JC= 10°C/W

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 noted. (Note 2)

PARAMETER

CONDITIONS

MIN

TYP

MAX

2.6

UNITS

Minimum Operating Voltage

Maximum Operating Voltage

Feedback Voltage

2.45

V

16

1.23

1.22

1.25

1.27

V

●

FB Pin Bias Current

V

= 1.25V (Note 3)

20

40

120

nA

µmhos

V/V

FB

Error Amp Transconductance

Error Amp Voltage Gain

Quiescent Current

∆I = 2µA

300

3.6

0

V

= 2.5V, Not Switching

5

1

mA

SHDN

Quiescent Current in Shutdown

Reference Line Regulation

Switching Frequency

= 0V, V = 3V

µA

IN

2.6V ≤ V ≤ 16V

0.01

2.7

0.05

%/V

IN

2.4

2.3

3

3.1

MHz

●

Switching Frequency in Foldback

Maximum Duty Cycle

V

= 0V

0.85

80

MHz

%

FB

●

73

Switch Current Limit

(Note 4)

1.5

2.1

240

0.01

4

3.1

340

1

A

Switch V

I

= 1A

SW

mV

µA

V

CESAT

Switch Leakage Current

Soft-Start Charging Current

SHDN Input Voltage High

SHDN Input Voltage Low

SHDN Pin Bias Current

V

= 5V

SW

SS

= 0.5V

2.5

2.4

6

0.5

V

= 3V

= 0V

16

0

32

0.1

µA

SHDN

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

of a device may be impaired.

temperature range are assured by design, characterization and correlation

with statistical process controls.

Note 2: The LT1946AE is guaranteed to meet performance specifications

from 0°C to 70°C. Specifications over the –40°C to 85°C operating

Note 3: Current flows out of the FB pin.

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

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

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LT1946A

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TYPICAL PERFOR A CE CHARACTERISTICS

Feedback Pin Voltage

Oscillator Frequency

Current Limit

1.28

3000

2700

2400

2100

1800

1500

1200

900

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

1.27

1.26

1.25

1.24

1.23

1.22

1.21

1.20

T

= –30°C

T

= 100°C

= 25°C

A

600

300

0

–50 –25

0

25

50

75 100 125

0

0.2

0.4

0.6

0.8

1

1.2

–50 –25

0

25

50

75 100 125

TEMPERATURE (°C)

FEEDBACK VOLTAGE (V)

TEMPERATURE (°C)

1946A G01

1946A G02

1946A G03

Switching Waveforms for

Figure 1 Circuit

Switch Saturation Voltage

Quiescent Current

0.35

0.30

0.25

0.20

0.15

0.10

0.05

0

4.0

3.8

3.6

3.4

3.2

3.0

2.8

2.6

2.4

2.2

V_OUT

100mV/DIV

AC COUPLED

V_SW

10V/DIV

0V

I_LI

0.5A/DIV

100ns/DIV

1946A G06

0

0.2 0.4 0.6 0.8

1

1.2 1.4 1.6

–50 –25

0

25

50

75 100 125

SWITCH CURRENT (A)

TEMPERATURE (°C)

1946A G04

1946A G05

Transient Response for

Figure 1 Circuit

Start-Up Waveforms for

Figure 1 Circuit

V_OUT

100mV/DIV

AC COUPLED

V_OUT

2V/DIV

I_IN

200mA/DIV

0A

I_LI

0.5A/DIV

250mA

I_LOAD

5V

0V

V_SHDN

150mA

50µs/DIV

1946A G07

R_LOAD= 250Ω

1ms/DIV

1946A G08

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LT1946A

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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.

External compensation consists of placing a resistor and

capacitor in series from V_Cto GND. Typical capacitor

rangeisfrom90pFto270pF.Typicalresistorrangeisfrom

25k to 120k.

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.

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 1.25V.

Connect resistive divider tap here. Minimize trace area at

FB. Set V_OUTaccording to V_OUT= 1.25 • (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, Exposed Pad): Ground. Tie both Pin 4 and

the exposed pad directly to local ground plane. The

ground metal to the exposed pad should be wide for better

heat dissipation. Multiple vias (local ground plane ↔

ground backplane) placed close to the exposed pad can

further aid in reducing thermal resistance.

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LT1946A

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BLOCK DIAGRA

SS

8

V

COMP

7

C

1

4µA

120k

90pF

5

SW

COMPARATOR

A2

–

+

DRIVER

R

Q

Q1

S

1.25V

6

+

–

V

IN

+

–

REFERENCE

A1

A3

0.01Ω

Σ

V

OUT

RAMP

GENERATOR

R1 (EXTERNAL)

FB

+

–

4

GND

0.5V

R2 (EXTERNAL)

÷ 3

2.7MHz

OSCILLATOR

EXPOSED

PAD

SHDN

3

2

SHUTDOWN

1946A F02

FB

Figure 2. Block Diagram

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LT1946A

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OPERATIO

a nominal value of 0.5V. This is accomplished via com-

parator A3. This feature reduces the minimum duty cycle

thatthepartcanachievethusallowingbettercontrolofthe

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

goes above 0.5V, the oscillator returns to the normal

frequencyof2.7MHz.Asoft-startfunctionisalsoprovided

by the LT1946A. When the part is brought out of shut-

down, 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

inFigure2.Theswitchcurrentisconstantlymonitoredand

not allowed to exceed the nominal value of 2.1A. If the

switch current reaches 2.1A, the SR latch is reset regard-

less of the output of comparator A2. This current limit

protects the power switch as well as various external

components connected to the LT1946A.

The LT1946A 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.

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

for the LT1946A. Frequency foldback is used to reduce the

oscillator frequency by one-third when the FB pin is below

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APPLICATIO S I FOR ATIO

Inductor Selection

Table 1. Recommended Inductors - LT1946A

MAX

DCR

(µH) (mΩ)

Size

LxWxH

(mm)

L

Several inductors that work well with the LT1946A are

listed in Table 1. This table is not complete, and there are

many other manufacturers and devices that can be used.

Consult each manufacturer for more detailed information

and for their entire selection of related parts, as many

differentsizesandshapesareavailable.Ferritecoreinduc-

tors should be used to obtain the best efficiency, as core

losses at 2.7MHz are much lower for ferrite cores than for

the cheaper powdered-iron ones. Choose an inductor that

can handle at least 1.5A without saturating, and ensure

that the inductor has a low DCR (copper-wire resistance)

to minimize I²R power losses. A 1.5µH to 4.7µH inductor

will be the best choice for most LT1946A designs. Note

that in some applications, the current handling require-

ments of the inductor can be lower, such as in the SEPIC

topology where each inductor only carries one-half of the

total switch current.

PART

VENDOR

RLF5018-1R5M2R1

RLF5018-2R7M1R8

RLF5018-4R7M1R4

RLF5018-100MR94

1.5

2.7

4.7

25

33

45

67

5.2x5.6x1.8 TDK

(847) 803-6100

www.tdk.com

10.0

LPO1704-122MC

LPO1704-222MC

1.2

2.2

80

120

5.5x6.6x1.0 Coilcraft

(800) 322-2645

www.coilcraft.com

CR43-2R2

CR43-3R3

2.2

3.3

71

86

4.5x4.0x3.2 Sumida

(847) 956-0666

www.sumida.com

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

TheinductorsshowninTable1werechosenforsmallsize.

For better efficiency, use similar valued inductors with a

larger volume.

voltage and temperature ranges. A 2.2µF to 20µF output

sn1946a 1946afs

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LT1946A

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APPLICATIO S I FOR ATIO

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capacitor is sufficient for most applications, but systems

with very low output currents may need only a 1µF or

smaller output capacitor. Solid tantalum or OSCON ca-

pacitorscanbeused,buttheywilloccupymoreboardarea

than a ceramic and will have a higher ESR. Always use a

capacitor with a sufficient voltage rating.

V

OUT

200mV/DIV

AC COUPLED

I

L1

Ceramic capacitors also make a good choice for the input

decoupling capacitor, which should be placed as close as

possible to the LT1946A. 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.

0.5A/DIV

1946A F03a

R

= 2.5k

C

50µs/DIV

Figure 3a. Transient Response Shows Excessive Ringing

Table 2. Ceramic Capacitor Manufacturers

V

OUT

200mV/DIV

Taiyo Yuden

AVX

(408) 573-4150

(803) 448-9411

(714) 852-2001

www.t-yuden.com

www.avxcorp.com

www.murata.com

AC COUPLED

Murata

I

L1

0.5A/DIV

Compensation

1946A F03b

TocompensatethefeedbackloopoftheLT1946A, aseries

resistor-capacitor network should be connected from the

COMPpintoGND.Formostapplications,acapacitorinthe

range of 90pF to 470pF will suffice. A good starting value

for the compensation capacitor, C_C, is 270pF. The com-

pensation resistor, R_C, is usually in the range of 20k to

100k. A good technique to compensate a new application

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

270pF capacitor for C_C. By adjusting the potentiometer

while observing the transient response, the optimum

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

process for the circuit of Figure 1. Figure 3a shows the

transient response with R_Cequal to 2.5k. The phase

marginispoorasevidencedbytheexcessiveringinginthe

output voltage and inductor current. In Figure 3b the value

of R_Cis increased to 6.5k, which results in a more damped

response. Figure 3c shows the results when R_Cis in-

creased further to 27.4k. 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.

R

= 6.5k

C

50µs/DIV

Figure 3b. Transient Response is Better

V

OUT

200mV/DIV

AC COUPLED

I

L1

0.5A/DIV

1946A F03c

R

= 27.4k

C

50µs/DIV

Figure 3c. Transient Response is Well Damped

Compensation-Theory

Like all other current mode switching regulators, the

LT1946A needs to be compensated for stable and efficient

operation. Two feedback loops are used in the LT1946A:

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.

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LT1946A

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APPLICATIO S I FOR ATIO

1

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

Z₂=

ESR Zero:

RHP Zero:

2• π •ESR•C_OUT

V

IN

²•R_L

2• π •V_OUT²•L

Z₃=

G_MP. G_MPacts as a current source where the output

current is proportional to the V_Cvoltage. Note that the

maximumoutputcurrentofG_MPisfiniteduetothecurrent

limit in the IC.

F_S

3

P >

3

High Frequency Pole:

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

calculated as follows:

Using the circuit of Figure 1 as an example, Table 3 shows

the parameters used to generate the bode plot shown in

Figure 5.

2

Table 3. Bode Plot Parameters

P =

1

Output Pole:

2• π •R_L•C_OUT

Parameter

Value

28

Units

Ω

Comment

R

L

Application Specific

Not Adjustable

Adjustable

1

C

2.2

10

µF

OUT

P =

Error Amp Pole:

Error Amp Zero:

2

R

MΩ

pF

2• π •R_O•C_C

O

C

270

27.4

12

R

C

kΩ

Adjustable

1

Z₁=

V

Application Specific

Not Adjustable

Application Specific

Not Adjustable

OUT

IN

2• π •R_C•C_C

5

V

G

MA

G

MP

L

40

µmho

mho

µH

1.25

V_OUT

A =

•G_MA•R_O•G_MP•R_L

5

DC Gain:

2.2

2.7

10

F

MHz

mΩ

S

ESR

–

+

G

V

MP

OUT

From Figure 5, the phase when the gain reaches 0dB is

122° giving a phase margin of 58°. This is more than

adequate. The cross-over frequency is 90kHz, which is

about 30 times lower than the frequency of the right half

planezeroZ2.Itisimportantthatthecross-overfrequency

beatleast3timeslowerthanthefrequencyoftheRHPzero

to achieve adequate phase margin.

ESR

R

L

C

+

OUT

1.250V

REFERENCE

V

C

R

1

2

G

MA

–

R

C

R

O

C

G

OUT

: TRANSCONDUCTANCE AMPLIFIER INSIDE IC

MA

MP

: POWER STAGE TRANSCONDUCTANCE AMPLIFIER

C

: OUTPUT CAPACITOR

R : OUTPUT RESISTANCE DEFINED AS V

DIVIDED BY I

(MAX)

LOAD

L

OUT

R1, R2: FEEDBACK RESISTOR DIVIDER NETWORK

R : OUTPUT RESISTANCE OF G

O

MA

R : COMPENSATION RESISTOR

C

C : COMPENSATION CAPACITOR

C

Figure 4. Boost Converter Equivalent Model

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LT1946A

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APPLICATIO S I FOR ATIO

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100

Setting Output Voltage

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

(see Figure 1) according to the following equation:

50

V_OUT

1.25V

R1= R2

– 1

0

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

–50

Layout Hints

100

1k

10k

100k

1M

FREQUENCY (Hz)

ThehighspeedoperationoftheLT1946Ademandscareful

attention to board layout. You will not get advertised

performance with careless layouts. Figure 6 shows the

recommended component placement for a boost con-

verter.

1946A FO5a

0

–100

GROUND PLANE

CSS

C1

58°

+

C

V

IN

R

–180

–200

1

2

3

4

8

7

6

5

R1

100

1k

10k

100k

1M

FREQUENCY (Hz)

L1

LT1946A

1946A FO5b

R2

SHUTDOWN

Figure 5. Gain and Phase Plots of Figure 1 Circuit

MULTIPLE

VIAs

Diode Selection

C2

GND

ASchottkydiodeisrecommendedforusewiththeLT1946A.

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.

V

OUT

19949 F04

NOTE: DIRECT HIGH CURRENT PATHS USING WIDE PC TRACES. MINIMIZE TRACE AREA AT

PIN 1(V_C) AND PIN 2(F_B). 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.

Figure 6. Recommended Component

Placement for Boost Converter

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LT1946A

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TYPICAL APPLICATIO S

Low Profile (<1.1mm Tall) Triple Output TFT Supply (10V, –10V, 20V)

D2

D3

V

ON

20V

5mA

C5

0.1µF

L1

1.5µH

D1

A

VDD

V

IN

10V

5V

475mA

6

5

R1

75k

V

SW

IN

3

8

7

OFF ON

SHDN

2

SS LT1946A FB

COMP

+

C2

20µF

C3

1µF

C1

4.7µF

V

GND*

4

C

1

R2

10.5k

C

SS

R

59k

C

100nF

C

150pF

C6

0.1µF

C1–C6: X5R or X7R

C1: 4.7µF, 6.3V

C2: 2× 10µF, 10V

C3: 1µF, 25V

D4

D5

C4

2.2µF

C4: 2.2µF, 10V

C5–C6: 0.1µF, 10V

V

OFF

D1: MICROSEMI UPS120 OR EQUIVALENT

D2–D5: ZETEX BAT54S OR EQUIVALENT

L1: COILCRAFT LP01704-152MC

–10V

10mA

1946A TA02

* EXPOSED PAD MUST ALSO BE GROUNDED

Transient Response

Efficiency

90

85

80

75

70

65

60

55

50

A_VDD

50mV/DIV

AC COUPLED

I_LI

0.5A/DIV

V

LOAD = 5mA

LOAD = 10mA

ON

OFF

350mA

200mA

A_VDDLOAD

0

100

200

300

400

500

A

VDD

LOAD CURRENT (mA)

100µs/DIV

1946A TA03

1946A TA04

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LT1946A

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TYPICAL APPLICATIO S

Triple Output TFT Supply Uses SEPIC Topology for Output Disconnect

D2

V

ON

23V

C4

10mA

0.22µF

D3

V

OFF

–12V

C5

0.22µF

10mA

L1

10µH

D1

A

VDD

V

IN

12V

12V ± 10%

250mA

6

5

SW

C3

1µF

L2

10µH

R1

V

IN

3

8

1

84.5k

OFF ON

SHDN

SS LT1946A FB

2

+

C2

C1

V

C

20µF

2.2µF

COMP

7

GND*

4

R2

9.76k

C

SS

100nF

D1: MICROSEMI UPS120 OR EQUIVALENT

D2–D3: CENTRAL SEMI CMDSH-3

L1–L2: TDK RLF5018-100MR94

C1–C5: X5R or X7R

C1: 2.2µF, 6.3V

C2: 2× 10µF, 16V

C3: 1µF, 25V

1946A TA09

* EXPOSED PAD MUST ALSO BE GROUNDED

C4: 0.22µF, 25V

C5: 0.22µF, 16V

MS8E Package

8-Lead Plastic MSOP

(Reference LTC DWG # 05-08-1662)

BOTTOM VIEW OF

EXPOSED PAD OPTION

2.06 ± 0.102

3.00 ± 0.102

(.118 ± .004)

(NOTE 3)

0.889 ± 0.127

(.035 ± .005)

2.794 ± 0.102

(.110 ± .004)

0.52

(.206)

REF

(.080 ± .004)

1

8

7 6

5

1.83 ± 0.102

(.072 ± .004)

5.23

(.206)

MIN

3.2 – 3.45

(.126 – .136)

3.00 ± 0.102

(.118 ± .004)

NOTE 4

2.083 ± 0.102

(.082 ± .004)

4.88 ± 0.1

(.192 ± .004)

DETAIL “A”

0.254

(.010)

0° – 6° TYP

GAUGE PLANE

0.65

(.0256)

BSC

0.42 ± 0.04

1

2

3

4

(.0165 ± .0015)

8

TYP

0.53 ± 0.015

(.021 ± .006)

1.10

(.043)

MAX

0.86

(.34)

REF

RECOMMENDED SOLDER PAD LAYOUT

DETAIL “A”

0.18

(.077)

SEATING

PLANE

NOTE:

0.22 – 0.38

(.009 – .015)

1. DIMENSIONS IN MILLIMETER/(INCH)

2. DRAWING NOT TO SCALE

0.13 ± 0.05

(.005 ± .002)

0.65

(.0256)

BCS

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.

MSOP (MS8E) 1001

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

sn1946a 1946afs

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

LT1946A

U

TYPICAL APPLICATIO S

Low Profile (<1.1mm Tall) Triple Output TFT Supply (8V, –8V, 24V)

D2

D3

D4

D5

V

ON

23V

5mA

C5

0.1µF

C6

0.1µF

C7

0.1µF

Efficiency

L1

90

85

80

75

70

65

60

55

50

D1

1.2µH

AV

8V

DD

V

IN

3.3V

375mA

6

5

R2

V

SW

IN

3

8

7

28.7k

OFF ON

SHDN

2

SS LT1946A FB

COMP

+

C2

C4

1µF

C1

20µF

4.7µF

V

GND*

4

C

1

R3

5.23k

C

SS

100nF

V

LOAD = 5mA

ON

OFF

LOAD = 10mA

C8

0.1µF

C1–C8: X5R or X7R

C1: 4.7µF, 6.3V

C2: 2× 10µF, 10V

C3: 2.2µF, 10V

C4: 1µF, 25V

D7

D6

0

100

200

300

400

C3

2.2µF

A

LOAD CURRENT (mA)

VDD

1946A TA06

C5, C6, C8: 0.1µF, 10V

C7: 0.1µF, 16V

V

OFF

–8V

D1: MICROSEMI UPS120 OR EQUIVALENT

D2–D7: ZETEX BAT54S OR EQUIVALENT

L1: COILCRAFT LP01704-122MC

10mA

1946A TA05

* EXPOSED PAD MUST ALSO BE GROUNDED

Transient Response

Start-Up Waveforms

A_VDD

5V/DIV

A_VDD

50mV/DIV

AC COUPLED

V_ON

10V/DIV

I_LI

0.5A/DIV

V_OFF

5V/DIV

350mA

I_LOAD

200mA

I_IN

0.5A/DIV

1946A TA07

1946A TA08

1ms/DIV

50µs/DIV

RELATED PARTS

PART NUMBER

LT1613

DESCRIPTION

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COMMENTS

V

= 0.9V to 10V, V

to 34V, I = 3mA, I < 1µA, ThinSOT^TM

OUT Q SD

SW

IN

LT1615/LT1615-1

300mA/0.75mA (I ), Constant Off-Time Step-Up

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SW

DC/DC Converter

LT1930/LT1930A

LT1946

1A (I ), 1.2MHz/2.2MHz, Step-Up DC/DC Converter

V

= 2.6V to 16V, V

to 34V, I = 4.2mA/5.5mA, I < 1µA, ThinSOT

OUT Q SD

SW

IN

1.5A (I ), 1.2MHz, Step-Up DC/DC Converter

= 2.45V to 16V, V

to 34V, I = 3.2mA, I < 1µA, MS8

OUT Q SD

SW

LT1961

1.5A (I ), 1.25MHz, Step-Up DC/DC Converter

= 3V to 25V, V

to 35V, I = 0.9mA, I < 6µA, MS8E

SW

OUT Q SD

ThinSOT is a trademark of Linear Technology Corporation.

sn1946a 1946afs

LT/TP 1102 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：	LT1946A
厂家：	Linear
描述：	2.7MHz Boost DC/DC Converter with 1.5A Switch and Soft-Start 2.7MHz升压型DC / DC转换器，具有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：314K)
中文：	中文翻译
下载：	下载PDF数据表文档文件

LT1946A [Linear]

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