LT1616ES6#TR_技术文档

LT1616

600mA, 1.4MHz Step-Down

Switching Regulator

in SOT-23

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FEATURES

DESCRIPTIO

The LT^®1616 is a current mode PWM step-down DC/DC

converter with internal 0.6A power switch, packaged in a

tiny 6-lead SOT-23. The wide input range of 3.6V to 25V

makes the LT1616 suitable for regulating a wide variety of

power sources, from 4-cell batteries and 5V logic rails to

unregulated wall transformers and lead-acid batteries. Its

high operating frequency allows the use of tiny, low cost

inductors and ceramic capacitors. With its internal com-

pensation eliminating additional components, a complete

400mA step-down regulator fits onto 0.15 square inches

of PC board area.

■

Wide Input Range: 3.6V to 25V

■

5V at 400mA from 7V to 25V Input

■

3.3V at 400mA from 4.7V to 25V Input

■

Fixed Frequency 1.4MHz Operation

■

Uses Tiny Capacitors and Inductors

■

Internally Compensated

■

Low Shutdown Current: <1µA

■

Low V_CESATSwitch: 220mV at 300mA

■

Tiny 6-Lead SOT-23 Package

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APPLICATIO S

The constant frequency current mode PWM architecture

and stable operation with ceramic capacitors results in

low, predictable output ripple. Current limiting provides

protectionagainstshortedoutputs.Thelowcurrent(<1µA)

shutdown provides complete output disconnect, enabling

easy power management in battery-powered systems.

■

Wall Transformer Regulation

■

Local Logic Supply Conversion:

12V to 5V

12V or 5V to 3.3V, 2.5V or 1.8V

■

Distributed Supply Regulation

■

Digital Cameras

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

■

Battery-Powered Equipment

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TYPICAL APPLICATIO

3.3V Step-Down Converter

Efficiency

D2

100

90

5

4

1

V

IN

V

BOOST

IN

4.5V TO 25V

C3

V

IN

= 5V

V

= 12V

IN

L1

10µH

LT1616

0.01µF

6

V

OUT

80

70

60

50

40

30

OFF ON

SHDN

SW

3.3V

300mA: V = 4.5V TO 25V

IN

GND

2

FB

3

V

= 20V

R1

16.5k

IN

D1

400mA: V = 4.7V TO 25V

C1

1µF

C2

10µF

R2

10k

C1: TAIYO-YUDEN TMK316BJ105

C2: TAIYO-YUDEN JMK316BJ106ML

D1: ON SEMICONDUCTOR MBR0530

D2: 1N4148

1616 TA01

100

200

LOAD CURRENT (mA)

500

0

300

400

L1: SUMIDA CR43-100

1616 G02

1

LT1616

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ABSOLUTE AXI U RATI GS

PACKAGE/ORDER I FOR ATIO

(Note 1)

Input Voltage (V_IN) ................................................. 25V

BOOST Pin Voltage ................................................. 35V

BOOST Pin Above SW Pin ...................................... 25V

SHDN Pin ............................................................... 25V

FB Voltage ................................................................ 6V

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

Operating 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

TOP VIEW

LT1616ES6

BOOST 1

GND 2

FB 3

6 SW

5 V

IN

4 SHDN

S6 PART MARKING

LTNB

S6 PACKAGE

6-LEAD PLASTIC SOT-23

T_JMAX= 125°C, θ_JA= 250°C/ W

Consult factory for parts specified with wider operating temperature ranges.

ELECTRICAL CHARACTERISTICS

The ● denotes specifications which apply over the full operating temperature range, otherwise specifications are at T_A= 25°C.

V_IN= 10V, V_BOOST= 15V, unless otherwise noted. (Note 2)

PARAMETER

CONDITIONS

MIN

TYP

3.35

1.25

150

1.9

MAX

3.6

UNITS

V

Undervoltage Lockout

Feedback Voltage

●

1.225

1.275

600

2.5

V

FB Pin Bias Current

V

FB

= Measured V + 10mV

nA

mA

µA

%/V

MHz

V

REF

Quiescent Current

Not Switching

Quiescent Current in Shutdown

Reference Line Regulation

Switching Frequency

Frequency Shift Threshold on FB Pin

Maximum Duty Cycle

Switch Current Limit

V

= 0V

0.01

0.005

1.4

2

SHDN

= 5V to 25V

= 1.1V

IN

FB

●

1

1.8

f

= 700kHz

0.44

87

SW

80

%

(Note 3)

630

850

220

mA

mV

µA

V

Switch V

I

= 300mA

350

10

CESAT

SW

Switch Leakage Current

Minimum Boost Voltage Above Switch

BOOST Pin Current

I

= 300mA

1.6

7

2.5

12

SW

mA

V

SHDN Input Voltage High

SHDN Input Voltage Low

SHDN Bias Current

1.8

0.4

V

SHDN

V

SHDN

= 3V

= 0V

8

0.01

15

0.1

µA

Note 3: Current limit guaranteed by design and/or correlation to static test.

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

Slope compensation reduces current limit at higher duty cycle.

of the device may be impaired.

Note 2: The LT1616E 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.

2

LT1616

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TYPICAL PERFOR A CE CHARACTERISTICS

Efficiency, V_OUT= 5V

Efficiency, V_OUT= 3.3V

Switch Voltage Drop

500

400

300

200

100

90

100

90

V

IN

= 8V

V

IN

= 5V

V

= 12V

IN

V

= 12V

IN

80

70

60

50

40

30

80

70

60

50

40

30

V

= 20V

V

IN

= 24V

IN

100

0

200

400

600

100

200

LOAD CURRENT (mA)

500

100

200

LOAD CURRENT (mA)

500

0

300

400

0

300

400

SWITCH CURRENT (mA)

1616 G03

1616 G01

1616 G02

Maximum Load Current

at V_OUT= 5V

Maximum Load Current

at V_OUT= 3.3V

BOOST Pin Current

500

400

300

200

100

500

400

300

200

100

16

14

12

10

L = 10µH

L = 4.7µH

L = 15µH

L = 10µH

L = 6.8µH

OUTPUT LIMITED

BY DISSIPATION

8

6

OUTPUT LIMITED

BY DISSIPATION

4

2

0

5

10

15

20

25

0

5

10

15

20

25

0

200

400

600

INPUT VOLTAGE (V)

SWITCH CURRENT (mA)

1616 G04

1616 G05

1616 G06

Switch Current Limit

Feedback Pin Voltage

Undervoltage Lockout

1.27

1.26

1.25

1.24

3.7

3.6

3.5

3.4

3.3

3.2

3.1

1000

800

600

400

200

0

TYPICAL

MINIMUM

1.23

1.22

–50

0

25

50

75

100

–50

0

25

50

75

100

–25

0

20

40

60

80

100

TEMPERATURE (°C)

DUTY CYCLE (%)

1616 G08

1616 G11

1616 G07

3

LT1616

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TYPICAL PERFOR A CE CHARACTERISTICS

Oscillator Frequency

SHDN Pin Current

120

100

2.00

1.75

1.50

1.25

80

60

1.00

0.75

40

20

0

0.50

0.25

0

5

10

15

20

25

–25

0

50

–50

75

100

25

SHDN PIN VOLTAGE

TEMPERATURE (°C)

1616 G10

1616 G09

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PI FU CTIO S

BOOST (Pin 1): The BOOST pin is used to provide a drive

voltage, higher than the input voltage, to the internal

bipolar NPN power switch.

SHDN (Pin 4): The SHDN pin is used to put the LT1616 in

shutdown mode. Tie to ground to shut down the LT1616.

Tie to 2V or more for normal operation. If the shutdown

feature is not used, tie this pin to the V_INpin.

GND(Pin2):TietheGNDpintoalocalgroundplanebelow

the LT1616 and the circuit components. Return the feed-

back divider to this pin.

V_IN(Pin 5): The V_INpin supplies current to the LT1616’s

internalregulatorandtotheinternalpowerswitch.Thispin

must be locally bypassed.

FB(Pin3):TheLT1616regulatesitsfeedbackpinto1.25V.

Connect the feedback resistor divider tap to this pin. Set

the output voltage according to V_OUT= 1.25V (1 + R1/R2).

A good value for R2 is 10k.

SW (Pin 6): The SW pin is the output of the internal power

switch. Connect this pin to the inductor, catch diode and

boost capacitor.

4

LT1616

W

BLOCK DIAGRA

V

5

IN

BOOST

1

INT REG

AND

UVLO

SHDN

4

Σ

SLOPE

COMP

R

S

Q

DRIVER

Q1

OSC

SW

6

FREQUENCY

FOLDBACK

V

C

g

m

1.25V

2

3

1616BD

GND

FB

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OPERATIO

(Refer to Block Diagram)

The LT1616 is a constant frequency, current mode Buck

regulator. The 1.4MHz oscillator enables an RS flip-flop,

turningontheinternal600mApowerswitchQ1. Anampli-

fier and comparator monitor the current flowing between

theV_INandSWpins,turningtheswitchoffwhenthiscurrent

reaches a level determined by the voltage at V_C. An error

amplifiermeasurestheoutputvoltagethroughanexternal

resistor divider tied to the FB pin. This amplifier servos the

switch current to regulate the FB pin voltage to 1.25V. An

active clamp on the V_Cnode provides current limit.

SHDN pin is used to place the LT1616 in shutdown,

disconnecting the output and reducing the input current

to less than 1µA.

The switch driver operates from either the input or from

the BOOST pin. An external capacitor and diode are used

to generate a voltage at the BOOST pin that is higher than

the input supply. This allows the driver to fully saturate the

internal bipolar NPN power switch for efficient operation.

The oscillator reduces the LT1616’s operating frequency

when the voltage at the FB pin is low. This frequency

foldback helps to control the output current during start-

up and overload.

An internal regulator provides power to the control cir-

cuitry. Thisregulatorincludesanundervoltagelockoutto

prevent switching when V is less than ~3.5V. The

IN

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LT1616

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APPLICATIO S I FOR ATIO

(second trace) and the inductor (third trace) increases.

When the switch turns off, the switch current immediately

drops to zero and the inductor current flows through the

catch diode D1, which clamps the switch node 0.4V below

ground. The voltage across the inductor in this state has

the opposite sense and is equal to the output voltage plus

the catch diode drop, so the inductor current begins to

decrease.Thefourthtraceshowstheoutputvoltageripple.

The LT1616 efficiently converts power from an input volt-

age source to a lower output voltage using an inductor for

energystorage.TheLT1616usesitsinternalpowerswitch

and an external catch diode (D1 of the application circuit

on the first page of this data sheet) to produce a pulse-

width modulated square wave. Inductor L1 and output

capacitorC2filterthissquarewavetoproduceaDCoutput

voltage. An error amplifier regulates the output by com-

paring the output (divided by the feedback resistor string

R1 and R2) to an internal reference. The LT1616 uses

current mode control; instead of directly modulating the

pulse width, the error amplifier controls the peak current

in the switch and inductor. Current mode control has sev-

eral advantages, including simplified loop compensation

and cycle-by-cycle current limiting.

At light loads, the inductor current may reach zero on each

pulse. The diode will turn off, and the switch voltage will

ring, asshowninFigure2. Thisisdiscontinuousmodeop-

eration, and is normal behavior for the switching regula-

tor. TheLT1616willalsoskippulseswhentheloadislight.

Figure 1 shows several waveforms of the application cir-

cuit on the front page of this data sheet. The circuit is

converting a 12V input to 3.3V at 300mA. The first trace is

the voltage at the SW pin. When the internal switch is on,

the SW pin voltage is near the 12V input. This applies a

voltage across inductor L1, and the current in the switch

V_SW

5V/DIV

I_L1

0.2A/DIV

1616 F02

V_IN= 12V

500ns/DIV

V_OUT= 5V

I_OUT= 18mA

V_SW

5V/DIV

Figure 2. Discontinuous Mode Operation

If the output is shorted to ground, the output voltage will

collapse and there will be very little voltage to reset the

current in the inductor. The LT1616 can sense this condi-

tionatitsFBpin.Inordertocontrolthecurrent,theLT1616

reduces its operating frequency, allowing more time for

the catch diode to reset the inductor current.

I_SW

0.2A/DIV

1616 F01a

200ns/DIV

The input and output voltages determine the duty cycle of

the switch. The inductor value combined with these volt-

ages determines the ripple current in the inductor. Along

with the switch current limit, the inductor ripple current

determines the maximum load current that the circuit can

supply. At minimum, the input and output capacitors are

required for stable operation. Specific values are chosen

based on allowable ripple and desired transient perfor-

mance. The rest of the applications information is mainly

concernedwithchoosingtheseandtheothercomponents

in an LT1616 application.

I_L1

0.2A/DIV

V_OUT

5mV/DIV

1616 F01b

200ns/DIV

Figure 1. Operating Waveforms of the LT1616

Converting 12V to 3.3V at 300mA

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LT1616

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APPLICATIO S I FOR ATIO

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Inductor Selection and Maximum Output Current

The duty cycle of the internal switch is:

DC = (V_OUT+ V_D)/(V_IN– V_SW+ V_D)

If your application calls for output current less than

400mA, you may be able to relax the value of the inductor

and operate with higher ripple current. This may allow you

topickaphysicallysmallerinductororonewithalowerDC

resistance. Be aware that these equations assume con-

tinuous inductor current. If the inductor value is low or the

loadcurrentislight,thentheinductorcurrentmaybecome

discontinuous. This occurs when ∆I_L= 2I_OUT. For details

of discontinuous mode operation, see Linear Technology

Application Note AN44. Also, high duty cycle operation

may require slightly higher inductor values to avoid sub-

harmonic oscillations. See AN19.

where V_Dis the forward voltage drop of the catch diode

(D1) and V_SWis the voltage drop of the internal switch.

Usually one is interested in DC at full load current, so you

can use V_D= V_SW= 0.4V. Note that the LT1616 has a

maximum guaranteed duty cycle of 0.8. This will limit the

minimum input voltage for a particular output voltage.

When the switch is off, the inductor sees the output

voltage plus the catch diode drop. This gives the peak-to-

peak ripple current in the inductor:

The maximum load current as a function of input voltage

is plotted in the Typical Performance Characteristics sec-

tion of this data sheet. Maximum load current for 3.3V and

5V outputs is shown for several values of L. At the highest

input voltages, the load current is limited by power dissi-

pation in the LT1616.

∆I_L= (1 – DC)(V_OUT+ V_D)/(L • f)

where f is the switching frequency of the LT1616 and L is

the value of the inductor. The average inductor current is

equal to the output current, so the peak inductor current

will be the output current plus one half of the ripple

current:

Choose an inductor that is intended for power applica-

tions. Table 1 lists several manufacturers and inductor

series. The saturation current of the inductor should be

above 0.5A. The RMS current rating should be equal to or

greater than output current. For indefinite operation into a

short circuit, the RMS current rating should be greater

than 0.7A. The DC resistance should be less than 0.5Ω in

order maintain circuit efficiency.

I_LPK= I_OUT+ ∆I_L/2.

To maintain output regulation, this peak current must be

less than the LT1616’s switch current limit I_LIM. I_LIMis at

least 630mA at low duty cycles, decreasing to 430mA at

80%dutycycle.Themaximumoutputcurrentisafunction

of the chosen inductor value:

Capacitor Selection

I_OUT(MAX)= I_LIM– ∆I_L/2.

A Buck regulator draws from its input a square wave of

current with peak-to-peak amplitude as high as the switch

current limit. The input capacitor (C1) must supply the AC

component of this current. An RMS current rating of

250mA is adequate for LT1616 circuits. The input capaci-

tor must bypass the LT1616 internal control circuitry and

any other circuitry that operates from the input source. A

1µF ceramic capacitor will satisfy both of these require-

ments. If the impedance of the input source is high (due to

long wires or filter components), additional bulk input

capacitance may be required. In high duty cycle applica-

tions (5V_INto 3.3V_OUT, for example), increase the input

capacitorto2.2µF.Itmaybepossibletoachievelowercost

by using an electrolytic capacitor (tantalum or aluminum)

If the inductor value is chosen so that the ripple current is

small, then the available output current will be near the

switch current limit. A good approach is to choose the

inductor so that the peak-to-peak inductor ripple is equal

to one third of the switch current limit. This leads to:

L = 3(1 – DC)(V_OUT+ V_D)/(I_LIM• f)

and

I_OUT(MAX)= (5/6)I_LIM

.

These expressions depend on duty cycle and therefore on

input voltage. Pick a nominal input voltage to calculate L,

then check the maximum available output current at the

minimum and maximum input voltages.

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LT1616

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Table 1. Inductor Vendors

Vendor

Murata

Sumida

Phone

URL

Part Series Comments

(404) 426-1300 www.murata.com

(847) 956-0666 www.sumida.com

LQH3C

Small, Low Cost, 2mm Height

CR43

CLS62

CLQ61

1:1 Coupled

1.5mm Height

Coilcraft

(847) 639-6400 www.coilcraft.com

DO1607C

DO1608C

DT1608C

Coiltronics (407) 241-7876 www.coiltronics.com CTXxx-1

TP1

1:1 Coupled Toroid

1.8mm Height

Toko

www.tokoam.com

3DF

D52LC

Table 2. Capacitor Vendors

Vendor

Phone

URL

Part Series

Comments

Taiyo-Yuden (408) 573-4150

www.t-yuden.com

www.avxcorp.com

Ceramic Caps X5R Dielectric

AVX

(803) 448-9411

(404) 436-1300

Ceramic Caps

Tantalum Caps

Murata

www.murata.com

Ceramic Caps

in combination with a 0.1µF ceramic capacitor. However,

input voltage ripple will be higher, and you may want to

include an additional 0.1µF ceramic a short distance away

fromtheLT1616circuitinordertofilterthehighfrequency

ripple. The input capacitor should be rated for the maxi-

mum input voltage.

Another constraint on the output capacitor is that it must

havegreaterenergystoragethantheinductor;ifthestored

energy in the inductor is transferred to the output, you

would like the resulting voltage step to be small compared

totheregulationvoltage. Fora5%overshoot, thisrequire-

ment becomes

2

The output capacitor has two essential functions. Along

with the inductor, it filters the square wave generated by

the LT1616 to produce the DC output. In this role it

determines the output ripple. The second function is to

store energy in order to satisfy transient loads and stabi-

lize the LT1616’s control loop.

C_OUT> 10 • L(I_LIM/V_OUT)

Finally, there must be enough capacitance for good tran-

sient performance. The last equation gives a good starting

point. Alternatively, you can start with one of the designs

in this data sheet and experiment to get the desired

performance. Figure 3 illustrates some of the trade-off

between different output capacitors. Figure 4 shows the

test circuit. The lowest trace shows total output current,

which jumps from 100mA to 250mA. The other traces

show the output voltage ripple and transient response

with different output capacitors. The capacitor value, size

and type are listed. Note that the time scale at 50µs per

divison is much larger than the switching period, so you

can’t see the output ripple at the switching frequency. The

output ripple appears as vertical broadening of the trace.

The first trace (C_OUT= 4.7µF) has peak-to-peak output

ripple of ~6mV, while the third trace shows peak-to-peak

ripple of ~15mV.

In most switching regulators the output ripple is deter-

mined by the equivalent series resistance (ESR) of the

outputcapacitor.BecausetheLT1616’scontrolloopdoesn’t

dependontheoutputcapacitor’sESRforstableoperation,

you are free to use ceramic capacitors to achieve very low

output ripple and small circuit size. You can estimate

output ripple with the following equations:

V_RIPPLE=∆I_L•ESRforelectrolyticcapacitors(tantalum

and aluminum)

V_RIPPLE= ∆I_L/(2π • f • C_OUT) for ceramic capacitors

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LT1616

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APPLICATIO S I FOR ATIO

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5

4

1

6

V

IN

V

IN

BOOST

SW

10V

LT1616

10µH

V

OUT

SHDN

3.3V

GND

2

FB

3

22Ω

33Ω

C

OUT

C_OUT= 4.7µF CERAMIC, CASE SIZE 0805

1616 F04

Figure 4. Circuit Used for Transient Load Test Shown in Figure 3

Regardless of which capacitor or combination of capaci-

tors you choose, you should do transient load tests to

evaluate the circuit’s stability. Avoid capacitors or combi-

nations that result in a ringing response. Problems may

occuriftheoutputcapacitanceisveryloworifahighvalue

inductor is used in combination with a large value, low

ESR capacitor.

C_OUT= 10µF CERAMIC, CASE SIZE 1206

The high performance (low ESR), small size and robust-

ness of ceramic capacitors make them the preferred type

forLT1616applications. However, allceramiccapacitors

arenotthesame. Manyofthehighervaluecapacitorsuse

poor dielectrics with high temperature and voltage

coefficients. In particular, Y5V types should be regarded

with suspicion. Stick with X7R and X5R types. Don’t be

afraid to run them at their rated voltage. Table 2 lists

several capacitor manufacturers.

C_OUT= 47µF, ESR 0.080Ω (SANYO POSCAP 6TPA47M)

C CASE

C_OUT= 100µF, ESR 0.150Ω (TANTALUM AVX

TPSC107M006R0150) C CASE

Catch Diode

V_OUT

A0.5ASchottkydiodeisrecommendedforthecatchdiode

D1. The ON Semiconductor MBR0530 is a good choice; it

is rated for 0.5A forward current and a maximum reverse

voltage of 30V. For circuits with V_INless than 20V, the

MBR0520L can be used. Other suitable diodes are the

Zetex ZHCS500TR and ZHCS750TR, and various versions

of the 1N5818.

20mV/DIV

I_LOAD

100mA/DIV

0

C_OUT= 100µF TANTALUM AND 2.2µF CERAMIC

Figure 3. Transient Load Response of the LT1616

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LT1616

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BOOST Pin Considerations

charged. Because the boost capacitor is charged with the

energy stored in the inductor, the circuit will rely on some

minimum load current to get the boost circuit running

properly. This minimum load will depend on input and

output voltages, and on the arrangement of the boost

circuit. The minimum load generally goes to zero once the

circuit has started. Figure 6 shows a plot of minimum load

to start and to run as a function of input voltage. In many

cases the discharged output capacitor will present a load

to the switcher which will allow it to start. The plots show

theworst-casesituationwhereV_INisrampingveryslowly.

Use a Schottky diode (such as the BAT-54) for the lowest

start-up voltage.

Capacitor C3 and diode D2 are used to generate a boost

voltagethatishigherthantheinputvoltage.Inmostcases

a 0.01µF capacitor and fast switching diode (such as the

1N4148 or 1N914) will work well. Figure 5 shows two

ways to arrange the boost circuit. The BOOST pin must be

more than 2.5V above the SW pin for best efficiency. For

outputsof3.3Vandabove, thestandardcircuit(Figure5a)

is best. For outputs between 2.8V and 3.3V, use a 0.033µF

capacitor and a small Schottky diode (such as the

BAT-54). For lower output voltages the boost diode can be

tiedtotheinput(Figure5b).ThecircuitinFigure5aismore

efficient because the BOOST pin current comes from a

lower voltage source. You must also be sure that the

maximumvoltageratingoftheBOOSTpinisnotexceeded.

Minimum Input Voltage V_OUT= 3.3V

7

V

D

= 3.3V

BOOST

OUT

= BAT54

The minimum operating voltage of an LT1616 application

is limited by the undervoltage lockout (<3.6V) and by the

maximum duty cycle as outlined above. For proper start-

up, the minimum input voltage is also limited by the boost

circuit.Iftheinputvoltageisrampedslowly,ortheLT1616

is turned on with its SHDN pin when the output is already

in regulation, then the boost capacitor may not be fully

BOOST DIODE

TIED TO OUTPUT

6

5

4

3

BOOST DIODE

TIED TO INPUT

V TO START

V TO RUN

D2

1

10

100

500

C3

BOOST

LT1616

LOAD CURRENT (mA)

1616 F06a

V

IN

V

OUT

V

IN

SW

Minimum Input Voltage V_OUT= 5V

GND

9

8

7

6

5

4

V

= 5V

BOOST

OUT

D

1616 F05a

BOOST DIODE

= BAT54

V

– V

BOOST

V

IN

TIED TO OUTPUT

BOOST

SW

OUT

MAX V

V

+ V

OUT

BOOST DIODE

TIED TO INPUT

(5a)

D2

V TO START

V TO RUN

C3

BOOST

LT1616

V

IN

V

IN

SW

OUT

GND

1616 F05b

V

– V

BOOST

V

BOOST

SW

IN

1

10

100

500

MAX V

2V

LOAD CURRENT (mA)

(5b)

1616 F06b

Figure 5. Two Circuits for Generating the Boost Voltage

Figure 6. The Minimum Input Voltage Depends

on Output Voltage, Load Current and Boost Circuit

10

LT1616

W U U

APPLICATIO S I FOR ATIO

U

the SHDN pin, the SW pin current will drop to essentially

zero. However, if the V_INpin is grounded while the output

is held high, then parasitic diodes inside the LT1616 can

pulllargecurrentsfromtheoutputthroughtheSWpinand

the V_INpin. Figure 7 shows a circuit that will run only when

the input voltage is present and that protects against a

shorted or reversed input.

Shorted Input Protection

If the inductor is chosen so that it won’t saturate exces-

sively, an LT1616 buck regulator will tolerate a shorted

output. There is another situation to consider in systems

where the output will be held high when the input to the

LT1616 is absent. This may occur in battery charging

applications or in battery backup systems where a battery

or some other supply is diode OR-ed with the LT1616’s

output. If the V_INpin is allowed to float and the SHDN pin

is held high (either by a logic signal or because it is tied to

V_IN), then the LT1616’s internal circuitry will pull its

quiescent current through its SW pin. This is fine if your

system can tolerate a few mA in this state. If you ground

PCB Layout

For proper operation and minimum EMI, care must be

taken during printed circuit board layout. Figure 8 shows

the high current paths in the buck regulator circuit. Note

that large, switched currents flow in the power switch, the

D4

5

1

6

V

BOOST

IN

LT1616

100k

4

V

OUT

SHDN

SW

GND

2

FB

3

BACKUP

D4: MBR0530

1616 F07

Figure 7. Diode D4 Prevents a Shorted Input from Discharging a

Backup Battery Tied to the Output; It Also Protects the Circuit from a

Reversed Input. The LT1616 Runs Only When the Input is Present

V

IN

SW

V

IN

SW

GND

(a)

(b)

I

C1

V

SW

L1

V

IN

SW

C1

D1

C2

GND

1616 F08

(c)

Figure 8. Subtracting the Current When the Switch is On (a) from the Current When the Switch is Off (b) Reveals the Path of the High

Frequency Switching Current (c). Keep This Loop Small. The Voltage on the SW and BOOST Nodes Will Also be Switched; Keep These

Nodes as Small as Possible. Finally, Make Sure the Circuit is Shielded with a Local Ground Plane

11

LT1616

W U U

U

APPLICATIO S I FOR ATIO

catch diode (D1) and the input capacitor (C1). The loop

formed by these components should be as small as

possible. Furthermore, the system ground should be tied

to the regulator ground in only one place; this prevents the

switched current from injecting noise into the system

ground. These components, along with the inductor and

output capacitor, should be placed on the same side of the

circuit board, and their connections should be made on

that layer. Place a local, unbroken ground plane below

these components, and tie this ground plane to system

groundatonelocation,ideallyatthegroundterminalofthe

output capacitor C2. Additionally, the SW and BOOST

nodes should be kept as small as possible. Finally, keep

theFBnodeassmallaspossiblesothatthegroundpinand

groundtraceswillshielditfromtheSWandBOOSTnodes.

Figure 9 shows component placement with trace, ground

plane and via locations. Include two vias near the GND pin

of the LT1616 to help remove heat from the LT1616 to the

ground plane.

Outputs Greater than 6V

For outputs greater than 6V, connect a diode (such as a

1N4148) from the SW pin to V_INto prevent the SW pin

fromringingaboveV_INduringdiscontinuousmodeopera-

tion. The 12V output circuit below shows the location of

this diode. Also note that for outputs above 10V, the input

voltage range will be limited by the maximum rating of the

BOOST pin. The 12V circuit shows how to overcome this

limitation using an additional Zener diode.

Other Linear Technology Publications

Application notes AN19, AN35 and AN44 contain more

detailed descriptions and design information for Buck

regulators and other switching regulators. The LT1376

data sheet has a more extensive discussion of output

ripple, loop compensation and stability testing. Design

Note DN100 shows how to generate a bipolar output

supply using a Buck regulator.

SHUTDOWN

V

IN

V

OUT

SYSTEM

GROUND

1616 F09

VIAS TO LOCAL GROUND PLANE

OUTLINE OF LOCAL GROUND PLANE

Figure 9. A Good PCB Layout Ensures Proper, Low EMI Operation

12

LT1616

U

TYPICAL APPLICATIO S

12V Output

D4

D3

D2

5

4

1

V

IN

V

BOOST

IN

16V TO 25V

C3

L1

33µH

LT1616

0.01µF

6

OFF ON

V

OUT

SHDN

SW

FB

12V

GND

2

300mA

R1

86.6k

D1

3

C1

1µF

25V

C2

R2

10k

2.2µF

16V

GND

1616 TA03

C1: TAIYO-YUDEN TMK316BJ105ML

C2: TAIYO-YUDEN EMK316BJ225ML

D1: ON SEMICONDUCTOR MBR0530

D2, D4: 1N4148

D3: CMPZ5234B 6.2V ZENER.

D3 LIMITS BOOST PIN VOLTAGE TO V + 6V

L1: COILCRAFT DO1608C-333

IN

1.8V Output

D2

5

4

1

6

V

IN

V

BOOST

SW

IN

3.6V TO 12V

C3

0.01µF

L1

4.7µH

LT1616

V

OUT

OFF ON

SHDN

400mA

GND

2

FB

3

R1

8.87k

D1

C1

1µF

16V

C2

R2

20k

10µF

6.3V

GND

1616 TA04

C1: TAIYO-YUDEN EMK212BJ105MG

C2: TAIYO-YUDEN JMK316BJ106ML

D1: ON SEMICONDUCTOR MBR0520L

D2: 1N4148 OR EQUIVALENT

L1: MURATA LQH3C4R7M24

13

LT1616

TYPICAL APPLICATIO S

U

2.5V Output

D2

5

4

1

6

V

IN

V

BOOST

SW

IN

3.6V TO 16V

C3

0.01µF

L1

LT1616

4.7µH

V

OUT

SHDN

OFF ON

2.5V

350mA

GND

2

FB

3

R1

10k

D1

C1

1µF

16V

C2

R2

10k

4.7µF

6.3V

GND

1616 TA05

C1: TAIYO-YUDEN EMK212BJ105MG

C2: TAIYO-YUDEN JMK212BJ475MG

D1: ON SEMICONDUCTOR MBR0520

D2: 1N4148

L1: MURATA LQH3C4R7M24

5V Output

D2

5

4

1

6

V

IN

V

BOOST

SW

IN

7V TO 25V

C3

L1

LT1616

0.01µF

15µH

V

OUT

OFF ON

SHDN

5V

300mA: V = 7V TO 25V

IN

GND

2

FB

3

R1

30.1k

D1

400mA: V = 8V TO 25V

IN

C1

1µF

25V

C2

R2

10k

10µF

6.3V

C1: TAIYO-YUDEN TMK316BJ105ML

C2: TAIYO-YUDEN JMK316BJ106MG

D1: ON SEMICONDUCTOR MBR0530

D2: 1N4148

1616 TA07

L1: TOKO A914BYW-150M

14

LT1616

U

PACKAGE DESCRIPTION ^{Dimensions in inches (millimeters) unless otherwise noted.}

S6 Package

6-Lead Plastic SOT-23

(LTC DWG # 05-08-1634)

2.80 – 3.00

(0.110 – 0.118)

(NOTE 3)

0.95

(0.037)

REF

1.90

(0.074)

REF

2.6 – 3.0

(0.110 – 0.118)

1.50 – 1.75

(0.059 – 0.069)

0.00 – 0.15

(0.00 – 0.006)

0.90 – 1.45

(0.035 – 0.057)

0.35 – 0.55

(0.014 – 0.022)

0.35 – 0.50

(0.014 – 0.020)

SIX PLACES (NOTE 2)

0.90 – 1.30

(0.035 – 0.051)

S6 SOT-23 0898

0.09 – 0.20

(0.004 – 0.008)

(NOTE 2)

NOTE:

1. DIMENSIONS ARE IN MILLIMETERS

2. DIMENSIONS ARE INCLUSIVE OF PLATING

3. DIMENSIONS ARE EXCLUSIVE OF MOLD FLASH AND METAL BURR

4. MOLD FLASH SHALL NOT EXCEED 0.254mm

5. PACKAGE EIAJ REFERENCE IS SC-74A (EIAJ)

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.

15

LT1616

TYPICAL APPLICATION

U

Bipolar Output DC/DC Converter

D2

5

4

1

V

IN

V

BOOST

IN

7.5V TO 25V

C3

L1A

22µH

LT1616

0.01µF

6

OFF ON

SHDN

SW

5V

200mA

•

GND

2

FB

3

R1

30.1k

D1

C1

1µF

25V

C2

R2

10k

10µF

6.3V

GND

C5

C1: TAIYO-YUDEN TMK316BJ105ML

L1B

22µH

1µF

C2, C4: TAIYO-YUDEN JMK316BJ106ML

C5: TAIYO-TUDEN JMK107BJ105MA

D1, D3: ON SEMICONDUCTOR MBR0530

D2: 1N4148

L1: 22µH 1:1 SUMIDA CLS62-220 OR

COILTRONICS CTX20-1

6.3V

•

C4

10µF

D3

6.3V

–5V

100mA

–5V LOAD SHOULD BE LESS THAN

1/2 5V LOAD, SEE DESIGN NOTE 100

1616 TA06

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sn1616 1616fs LT/TP 0201 4K • PRINTED IN USA

16 ^{LinearTechnology Corporation}

1630 McCarthy Blvd., Milpitas, CA 95035-7417

●

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

LINEAR TECHNOLOGY CORPORATION 2000


型号：	LT1616ES6#TR
厂家：	Linear
描述：	LT1616 - 600mA, 1.4MHz Step-Down Switching Regulator in SOT-23; Package: SOT; Pins: 6; Temperature Range: -40°C to 85°C 稳压器开关式稳压器或控制器电源电路开关式控制器光电二极管
文件：	总16页 (文件大小：277K)
中文：	中文翻译
下载：	下载PDF数据表文档文件

LT1616ES6#TR [Linear]

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