LTC3406ABES5-2#TRPBF

LTC3406AB-2

2.25MHz, 600mA

Synchronous Step-Down

Regulator in ThinSOT

DescripTion

TheLTC^®3406AB-2isahighefficiencymonolithicsynchro-

nous buck regulator using a constant frequency, current

mode architecture. Supply current with no load is 200µA

and drops to <1µA in shutdown. The 2.5V to 5.5V input

voltage range makes the LTC3406AB-2 ideally suited for

single Li-Ion battery-powered applications. 100% duty

cycle provides low dropout operation, extending battery

life in portable systems. PWM pulse skipping mode op-

eration provides very low output ripple voltage for noise

sensitive applications.

FeaTures

n

High Efficiency: Up to 96%

n

600mA Output Current

n

2.5V to 5.5V Input Voltage Range

n

2.25MHz Constant Frequency Operation

n

No Schottky Diode Required

n

Low Dropout Operation: 100% Duty Cycle

n

±±2% OutOu%ꢀoluage%AccOracy

n

Low Quiescent Current: 200µA

n

0.6V Reference Allows Low Output Voltages

n

Shutdown Mode Draws <1µA Supply Current

n

Internal Soft-Start Limits Inrush Current

Switching frequency is internally set at 2.25MHz, allowing

the use of small surface mount inductors and capacitors.

The internal synchronous switch increases efficiency and

eliminates the need for an external Schottky diode. Low

outputvoltagesareeasilysupportedwiththe0.6Vfeedback

reference voltage. The LTC3406AB-2 is available in a low

profile (1mm) ThinSOT package. Refer to LTC3406A for

applications that require Burst Mode^®operation.

n

Current Mode Operation for Excellent Line and

Load Transient Response

n

Overtemperature Protected

Low Profile (1mm) ThinSOT^TMPackage

n

applicaTions

n

Cellular Telephones

n

L, LT, LTC and LTM are registered trademarks of Linear Technology Corporation. Burst Mode

is a registered trademark of Linear Technology Corporation. ThinSOT is a registered trademark

of Linear Technology Corporation. All other trademarks are the property of their respective

owners. Protected by U.S. Patents including 5481178, 6580258

Personal Navigation Devices

n

Wireless and DSL Modems

n

Digital Still Cameras

n

Media Players

n

Portable Instruments

Typical applicaTion

Efficiency vs Output Current

100

V

= 1.8V

OUT

2.2µH*

V

90

80

70

60

50

40

30

20

10

0

OUT

V

IN

V

SW

1.8V

IN

†

22pF

C

600mA

IN

C

10µF

CER

**

4.7µF

CER

OUT

LTC3406AB-2

RUN

GND

V

FB

619k

*MURATA LQH32CN2R2M33

**TAIYO YUDEN JMK316BJ106

^†TAIYO YUDEN JMK212BJ475

309k

3406AB2 TA01a

V

= 2.7V

= 3.6V

= 4.2V

IN

0.1

1

10

100

1000

OUTPUT CURRENT (mA)

3406AB2 TA01b

3406ab2fa

1

For more information www.linear.com/LTC3406AB-2

LTC3406AB-2

absoluTe MaxiMuM raTinGs

pin conFiGuraTion

(Note 1)

TOP VIEW

Input Supply Voltage....................................–0.3V to 6V

RUN 1

GND 2

SW 3

5 V

4 V

FB

IN

RUN, V Voltages .......................................–0.3V to V

FB

IN

SW Voltage (DC)........................... –0.3V to (V + 0.3V)

IN

P-Channel Switch Source Current

S5 PACKAGE

5-LEAD PLASTIC TSOT-23

(DC) (Note 7) .......................................................800mA

N-Channel Switch Sink Current (DC) (Note 7) .....800mA

Peak SW Sink and Source Current (Note 7).............1.3A

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

Maximum Junction Temperature (Notes 3, 6)....... 125°C

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

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

T

= 125°C, θ = 250°C/W, θ = 90°C/W

JMAX

JA JC

orDer inForMaTion

LEAD FREE FINISH

TAPE AND REEL

PART MARKING

PACKAGE DESCRIPTION

TEMPERATURE RANGE

LTC3406ABES5-2#PBF

LTC3406ABES5-2#TRPBF LTDBB

5-Lead Plastic TSOT-23

–40°C to 85°C

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

Consult LTC Marketing for information on non-standard lead based finish parts.

For more information on lead free part marking, go to: http://www.linear.com/leadfree/

For more information on tape and reel specifications, go to: http://www.linear.com/tapeandreel/

3406ab2fa

2

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LTC3406AB-2

elecTrical characTerisTics ^Thel denotes the specifications which apply over the full operating

temperature range, otherwise specifications are at T_A= 25°C. V_IN= 3.6V unless otherwise specified.

SYMBOL

PARAMETER

CONDITIONS

MIN

0.5880

0.75

TYP

MAX

30

UNITS

nA

l

I

Feedback Current

VFB

V

FB

Regulated Feedback Voltage

Reference Voltage Line Regulation

Peak Inductor Current

(Note 4)

0.6

0.04

1

0.6120

0.4

V

IN

= 2.5V to 5.5V (Note 4)

%/V

A

DV

FB

I

PK

V

= 3V, V = 0.5V

1.25

IN

FB

Duty Cycle < 35%

V

Output Voltage Load Regulation

Input Voltage Range

0.5

%

V

LOADREG

l

2.5

1.8

5.5

IN

I

Input DC Bias Current

Active

Shutdown

(Note 5)

S

V

= 0.63V

200

0.1

300

1

µA

FB

RUN

= 0V, V = 5.5V

IN

f

Oscillator Frequency

V = 0.6V

FB

2.25

0.23

0.21

0.01

0.9

2.7

0.35

1

MHz

W

OSC

R

DS(ON)

R

DS(ON)

of P-Channel FET

of N-Channel FET

I

= 100mA

PFET

SW

I

= –100mA

W

NFET

I

t

SW Leakage

V

RUN

= 0V, V = 0V or 5V, V = 5V

µA

ms

V

LSW

SW

IN

Soft-Start Time

RUN Threshold

RUN Leakage Current

V from 10% to 90% Full-Scale

FB

0.6

0.3

1.2

1.5

1

SOFT-START

l

V

1

RUN

I

0.01

µA

Note 1: Stresses beyond those listed under Absolute Maximum Ratings

may cause permanent damage to the device. Exposure to any Absolute

Maximum Rating condition for extended periods may affect device

reliability and lifetime.

Note 4: The LTC3406AB-2 is tested in a proprietary test mode that

connects V to the output of the error ampliﬁer.

Note 5: Dynamic supply current is higher due to the gate charge being

FB

delivered at the switching frequency.

Note 2: The LTC3406AB-2E is guaranteed to meet performance

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

operating temperature range are assured by design, characterization and

correlation with statistical process controls.

Note 6: This IC includes overtemperature protection that is intended

to protect the device during momentary overload conditions. Junction

temperature will exceed 125°C when overtemperature protection is active.

Continuous operation above the specified maximum operating junction

temperature may impair device reliability.

Note 3: T is calculated from the ambient temperature T and power

J

A

dissipation P according to the following formula:

D

Note 7: Limited by long term current density considerations.

LTC3406AB-2: T = T + (P )(250°C/W)

J

A

D

3406ab2fa

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LTC3406AB-2

Typical perForMance characTerisTics

(From Figure 1a Except for the Resistive Divider Resistor Values)

Efficiency vs Input Voltage

Efficiency vs Load Current

Efficiency vs Input Voltage

100

90

80

70

60

50

40

30

20

10

0

100

90

80

70

60

50

40

30

20

10

0

100

90

80

70

60

50

40

30

20

10

0

V

= 1.2V

OUT

I

= 10mA

= 100mA

= 600mA

I

= 10mA

= 100mA

= 600mA

L

V

= 2.7V

= 3.6V

= 4.2V

IN

V

= 1.8V

3

V

= 1.2V

3

OUT

2

4

5

6

2

4

5

6

0.1

1

10

100

1000

OUTPUT CURRENT (mA)

INPUT VOLTAGE (V)

3406AB2 G02

3406AB2 G01

3406AB2 G03

Reference Voltage vs

Temperature

Efficiency vs Load Current

Efficiency vs Input Voltage

100

90

80

70

60

50

40

30

20

10

0

0.615

0.610

0.605

0.600

100

90

80

70

60

50

40

30

20

10

0

V

= 3.6V

IN

V

= 2.5V

OUT

0.595

0.590

0.585

I

= 10mA

= 100mA

= 600mA

L

V

= 2.7V

= 3.6V

= 4.2V

IN

V

= 2.5V

3

OUT

50

TEMPERATURE (°C)

100 125

2

4

5

6

–50 –25

0

25

75

0.1

1

10

100

1000

INPUT VOLTAGE (V)

OUTPUT CURRENT (mA)

3406AB2 G04

3406AB2 G05

3406AB2 G06

Oscillator Frequency vs

Temperature

Oscillator Frequency vs

Supply Voltage

Output Voltage vs Load Current

2.50

2.45

2.40

2.35

2.30

2.25

2.20

2.15

2.10

2.05

2.00

2.4

2.3

2.2

2.1

2.0

1.9

1.8

1.820

1.816

V

= 1.8V

V

= 3.6V

OUT

IN

1.812

1.808

1.804

1.800

1.796

1.792

1.788

1.784

1.780

V

IN

V

IN

V

IN

= 2.7V

= 3.6V

= 4.2V

4.5

INPUT VOLTAGE (V)

5

2

2.5

3

3.5

4

5.5

6

0

400

200

OUTPUT CURRENT (mA)

600

–50

0

25

50

75 100 125

–25

TEMPERATURE (°C)

3406AB2 G08

3406AB2 G09

3406AB2 G07

3406ab2fa

4

For more information www.linear.com/LTC3406AB-2

LTC3406AB-2

Typical perForMance characTerisTics

(From Figure 1a Except for the Resistive Divider Resistor Values)

R_DS(ON)vs Input Voltage

R_DS(ON)vs Temperature

0.40

0.35

0.30

0.25

0.40

0.35

0.30

V

= 3.6V

IN

V

IN

= 2.7V

0.25

0.20

0.15

0.10

0.05

MAIN SWITCH

V

= 4.2V

IN

SYNCHRONOUS

SWITCH

0.20

0.15

0.10

SYNCHRONOUS SWITCH

MAIN SWITCH

0

4

6

7

–25

0

50

75 100 125

0

1

2

3

5

–50

25

INPUT VOLTAGE (V)

TEMPERATURE (°C)

3406AB2 G10

3406AB2 G11

Dynamic Supply Current

vs Temperature

Dynamic Supply Current

300

250

200

150

100

50

300

250

200

150

V

LOAD

= 1.2V

= 0A

OUT

V

LOAD

= 3.6V

IN

OUT

I

= 1.2V

= 0A

I

PULSE SKIPPING MODE

100

50

0

4.5

INPUT VOLTAGE (V)

5

2

2.5

3

3.5

4

5.5

6

50

TEMPERATURE (°C)

100 125

–50 –25

0

25

75

3406AB2 G12

3406AB2 G13

Switch Leakage vs Temperature

Switch Leakage vs Input Voltage

140

120

1000

900

800

700

600

500

400

300

200

100

0

RUN = 0V

100

80

60

40

20

MAIN SWITCH

SYNCHRONOUS

SWITCH

SYNCHRONOUS

SWITCH

0

50

TEMPERATURE (°C)

100 125

0

1

3

4

5

6

–50 –25

0

25

75

2

INPUT VOLTAGE (V)

3406AB2 G15

3406AB2 G14

3406ab2fa

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LTC3406AB-2

Typical perForMance characTerisTics

(From Figure 1a Except for the Resistive Divider Resistor Values)

Start-Up from Shutdown

Load Step

RUN

2V/DIV

V

OUT

200mV/DIV

V

OUT

I

L

2V/DIV

500mA/DIV

I

L

I

LOAD

500mA/DIV

3406AB2 G17

3406AB2 G16

V

I

= 3.6V

V

I

= 3.6V

20µs/DIV

400µs/DIV

IN

OUT

IN

OUT

= 1.8V

= 0mA TO 600mA

= 600mA (3Ω RES)

LOAD

Load Step

V

OUT

100mV/DIV

OUT

100mV/DIV

I

L

500mA/DIV

I

LOAD

500mA/DIV

LOAD

500mA/DIV

3406AB2 G18

3406AB2 G19

V

LOAD

= 3.6V

V

= 3.6V

IN

20µs/DIV

IN

= 1.8V

OUT

I

= 50mA TO 600mA

I

LOAD

= 100mA TO 600mA

Load Step

Discontinuous Operation

SW

2V/DIV

V

OUT

100mV/DIV

V

OUT

I

L

20mV/DIV

500mA/DIV

AC COUPLED

I

LOAD

I

500mA/DIV

L

200mA/DIV

3406AB2 G20

3406AB2 G21

V

LOAD

= 3.6V

V

LOAD

= 3.6V

IN

20µs/DIV

400ns/DIV

IN

= 1.8V

OUT

I

= 200mA TO 600mA

I

= 25mA

3406ab2fa

6

For more information www.linear.com/LTC3406AB-2

LTC3406AB-2

pin FuncTions

RUN (Pin 1): Run Control Input. Forcing this pin above

1.5V enables the part. Forcing this pin below 0.3V shuts

down the device. In shutdown, all functions are disabled

drawing <1µA supply current. Do not leave RUN floating.

V (Pin 4): Main Supply Pin. Must be closely decoupled

IN

to GND, Pin 2, with a 2.2µF or greater ceramic capacitor.

V (Pin 5): Feedback Pin. Receives the feedback voltage

FB

from an external resistive divider across the output.

GND (Pin 2): Ground Pin.

SW (Pin 3): Switch Node Connection to Inductor. This pin

connectstothedrainsoftheinternalmainandsynchronous

power MOSFET switches.

FuncTional DiaGraM

SLOPE

COMP

OSC

V

IN

4

FREQ

SHIFT

–

+

V

FB

5

+

–

5Ω

0.6V

+

–

I

COMP

EA

Q

S

R

SWITCHING

LOGIC

RS LATCH

V

ANTI-

SHOOT-

THRU

AND

IN

BLANKING

CIRCUIT

SW

3

RUN

1

0.6V REF

+

–

SHUTDOWN

I

RCMP

2

GND

3406AB2 BD

3406ab2fa

7

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LTC3406AB-2

operaTion ^{(Refer to Functional Diagram)}

Main Control Loop

pulses in pulse skipping mode operation to maintain out-

put regulation. Refer to the LTC3406A data sheet if Burst

Mode operation is preferred.

The LTC3406AB-2 uses a constant frequency, current

mode step-down architecture. Both the main (P-channel

MOSFET)andsynchronous(N-channelMOSFET)switches

areinternal.Duringnormaloperation,theinternaltoppower

MOSFET is turned on each cycle when the oscillator sets

the RS latch, and turned off when the current comparator,

Dropout Operation

Astheinputsupplyvoltagedecreasestoavalueapproach-

ing the output voltage, the duty cycle increases toward the

maximumon-time.Furtherreductionofthesupplyvoltage

forces the main switch to remain on for more than one

cycle until it reaches 100% duty cycle. The output voltage

willthenbedeterminedbytheinputvoltageminusthevolt-

age drop across the P-channel MOSFET and the inductor.

I

, resets the RS latch. The peak inductor current at

COMP

of error amplifier EA. When the load current increases,

it causes a slight decrease in the feedback voltage, V ,

COMP

whichI

resetstheRSlatch,iscontrolledbytheoutput

FB

relative to the 0.6V reference, which in turn, causes the

EA amplifier’s output voltage to increase until the average

inductor current matches the new load current. While the

top MOSFET is off, the bottom MOSFET is turned on until

either the inductor current starts to reverse, as indicated

Animportantdetailtorememberisthatatlowinputsupply

voltages, the R

of the P-channel switch increases

DS(ON)

(see Typical Performance Characteristics). Therefore,

the user should calculate the power dissipation when the

LTC3406AB-2 is used at 100% duty cycle with low input

voltage (See Thermal Considerations in the Applications

Information section).

bythecurrentreversalcomparatorI

of the next clock cycle.

,orthebeginning

RCMP

The main control loop is shut down by grounding RUN,

resetting the internal soft-start. Re-enabling the main

control loop by pulling RUN high activates the internal

soft-start, which slowly ramps the output voltage over

approximately 0.9ms until it reaches regulation.

Slope Compensation and Inductor Peak Current

Slope compensation provides stability in constant fre-

quency architectures by preventing subharmonic oscil-

lations at high duty cycles. It is accomplished internally

by adding a compensating ramp to the inductor current

signal at duty cycles in excess of 40%. Normally, this

results in a reduction of maximum inductor peak current

for duty cycles >40%. However, the LTC3406AB-2 uses

a patented scheme that counteracts this compensating

ramp, which allows the maximum inductor peak current

to remain unaffected throughout all duty cycles.

Pulse Skipping Mode Operation

At light loads, the inductor current may reach zero or

reverse on each pulse. The bottom MOSFET is turned off

by the current reversal comparator, I

, and the switch

RCMP

voltage will ring. This is discontinuous mode operation,

and is normal behavior for the switching regulator. At

very light loads, the LTC3406AB-2 will automatically skip

3406ab2fa

8

For more information www.linear.com/LTC3406AB-2

LTC3406AB-2

applicaTions inForMaTion

The basic LTC3406AB-2 application circuit is shown on

the front page. External component selection is driven by

the load requirement and begins with the selection of L

Table 1. Representative Surface Mount Inductors

PART

NUMBER

VALUE

(µH)

DCR

MAX DC

SIZE

3

(W MAX) CURRENT (A)

W × L × H (mm )

followed by C and C

.

Sumida

CDRH3D16

1.5

2.2

3.3

4.7

0.043

0.075

0.110

0.162

1.55

1.20

1.10

0.90

3.8 × 3.8 × 1.8

IN

OUT

Inductor Selection

Sumida

CMD4D06

2.2

3.3

4.7

0.116

0.174

0.216

0.950

0.770

0.750

3.5 × 4.3 × 0.8

For most applications, the value of the inductor will fall in

the range of 1µH to 4.7µH. Its value is chosen based on the

desired ripple current. Large value inductors lower ripple

current and small value inductors result in higher ripple

Panasonic

ELT5KT

3.3

4.7

0.17

0.20

1.00

0.95

4.5 × 5.4 × 1.2

2.5 × 3.2 × 2.0

currents. Higher V or V

also increases the ripple cur-

IN

OUT

Murata

LQH32CN

1.0

2.2

4.7

0.060

0.097

0.150

1.00

0.79

0.65

rent as shown in equation 1. A reasonable starting point

for setting ripple current is

D

I = 240mA (40% of 600mA).

L









C and C

Selection

V_OUT

1

IN

OUT

DI_L=

V_OUT1−





f L

( )( )

V

Incontinuousmode,thesourcecurrentofthetopMOSFET

is a square wave of duty cycle V /V . To prevent large

IN

(1)

OUT IN

The DC current rating of the inductor should be at least

equal to the maximum load current plus half the ripple

current to prevent core saturation. Thus, a 720mA

rated inductor should be enough for most applications

(600mA + 120mA). For better efﬁciency, choose a low

DC-resistance inductor.

voltage transients, a low ESR input capacitor sized for the

maximumRMScurrentmustbeused.ThemaximumRMS

capacitor current is given by:



^1/2

V_OUTV − V

(

)

IN

OUT





C_INrequired I_RMS≅ I_OMAX

V

IN

Inductor Core Selection

This formula has a maximum at V = 2V , where

IN

OUT

I

= I /2. This simple worst-case condition is com-

RMS

OUT

Different core materials and shapes will change the

size/current and price/current relationship of an induc-

tor. Toroid or shielded pot cores in ferrite or permalloy

materials are small and don’t radiate much energy, but

generally cost more than powdered iron core inductors

with similar electrical characteristics. The choice of which

style inductor to use often depends more on the price vs

sizerequirementsandanyradiatedfield/EMIrequirements

than on what the LTC3406AB-2 requires to operate. Table

1 shows some typical surface mount inductors that work

well in LTC3406AB-2 applications.

monlyusedfordesignbecauseevensignificantdeviations

do not offer much relief. Note that the capacitor manu-

facturer’s ripple current ratings are often based on 2000

hours of life. This makes it advisable to further derate the

capacitor, or choose a capacitor rated at a higher tem-

perature than required. Always consult the manufacturer

if there is any question.

The selection of C

is driven by the required effective

OUT

series resistance (ESR).

3406ab2fa

9

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LTC3406AB-2

applicaTions inForMaTion

Typically,oncetheESRrequirementforC hasbeenmet,

the long wires can potentially cause a voltage spike at V ,

OUT

IN

theRMScurrentratinggenerallyfarexceedstheI

large enough to damage the part.

RIPPLE(P-P)

is determined by:

requirement. The output ripple DV

OUT

When choosing the input and output ceramic capacitors,

choose the X5R or X7R dielectric formulations. These

dielectrics have the best temperature and voltage char-

acteristics of all the ceramics for a given value and size.











1

DV_OUT≅ DI_LESR+

8fC

_OUT

where f = operating frequency, C

= output capacitance

OUT

Output Voltage Programming

and DI = ripple current in the inductor. For a fixed output

L

voltage, the output ripple is highest at maximum input

In the adjustable version, the output voltage is set by a

resistive divider according to the following formula:

voltage since DI increases with input voltage.

L

Aluminumelectrolyticanddrytantalumcapacitorsareboth

available in surface mount configurations. In the case of

tantalum, it is critical that the capacitors are surge tested

for use in switching power supplies. An excellent choice is

the AVX TPS series of surface mount tantalum. These are

specially constructed and tested for low ESR so they give

the lowest ESR for a given volume. Other capacitor types

include Sanyo POSCAP, Kemet T510 and T495 series, and

Sprague 593D and 595D series. Consult the manufacturer

for other specific recommendations.

R2

R1





V_OUT= 0.6V 1+









(2)

The external resistive divider is connected to the output,

allowing remote voltage sensing as shown in Figure 1.

0.6V ≤ V

≤ 5.5V

OUT

R2

Using Ceramic Input and Output Capacitors

V

FB

LTC3406AB-2

GND

R1

Higher values, lower cost ceramic capacitors are now

becoming available in smaller case sizes. Their high

ripple current, high voltage rating and low ESR make

them ideal for switching regulator applications. Because

the LTC3406AB-2’s control loop does not depend on

the output capacitor’s ESR for stable operation, ceramic

capacitors can be used freely to achieve very low output

ripple and small circuit size.

3406AB2 F01

Figure 1. Setting the LTC3406AB-2 Output Voltage

Efficiency Considerations

Theefficiencyofaswitchingregulatorisequaltotheoutput

power divided by the input power times 100%. It is often

useful to analyze individual losses to determine what is

limiting the efficiency and which change would produce

the most improvement. Efficiency can be expressed as:

However, care must be taken when ceramic capacitors

are used at the input and the output. When a ceramic

capacitor is used at the input and the power is supplied

by a wall adapter through long wires, a load step at the

Efficiency = 100% – (L1 + L2 + L3 + ...)

output can induce ringing at the input, V . At best, this

IN

where L1, L2, etc. are the individual losses as a percent-

age of input power.

ringing can couple to the output and be mistaken as loop

instability. At worst, a sudden inrush of current through

3406ab2fa

10

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LTC3406AB-2

applicaTions inForMaTion

2

Although all dissipative elements in the circuit produce

losses, two main sources usually account for most of the

2. I R losses are calculated from the resistances of the

internal switches, R , and external inductor R . In

SW

L

lossesinLTC3406AB-2circuits:V quiescentcurrentand

continuous mode, the average output current flowing

through inductor L is “chopped” between the main

switch and the synchronous switch. Thus, the series

resistance looking into the SW pin is a function of both

top and bottom MOSFET R

(DC) as follows:

IN

2

I R losses. The V quiescent current loss dominates the

efficiency loss at very low load currents whereas the I R

IN

2

loss dominates the efficiency loss at medium to high load

currents. In a typical efficiency plot, the efficiency curve at

very low load currents can be misleading since the actual

power lost is of no consequence as illustrated in Figure 2.

and the duty cycle

DS(ON)

R

SW

= (R )(DC) + (R )(1 – DC)

DS(ON)TOP DS(ON)BOT

The R

for both the top and bottom MOSFETs can

DS(ON)

1

V

= 3.6V

IN

be obtained from the Typical Performance Character-

2

istics curves. Thus, to obtain I R losses, simply add

0.1

R

to R and multiply the result by the square of the

SW

L

average output current.

0.01

OtherlossesincludingC andC ESRdissipativelosses

IN

OUT

and inductor core losses generally account for less than

2% total additional loss.

0.001

V

= 1.2V

= 1.8V

= 2.5V

OUT

Thermal Considerations

0.0001

0.1

1

10

100

1000

InmostapplicationstheLTC3406AB-2doesnotdissipate

much heat due to its high efficiency. But, in applications

where the LTC3406AB-2 is running at high ambient tem-

perature with low supply voltage and high duty cycles,

such as in dropout, the heat dissipated may exceed the

maximumjunctiontemperatureofthepart.Ifthejunction

temperature reaches approximately 150°C, both power

switches will be turned off and the SW node will become

high impedance.

OUTPUT CURRENT (mA)

3406AB2 F02

Figure 2. Power Loss vs Load Current

1. The V quiescent current is due to two components:

IN

the DC bias current as given in the electrical charac-

teristics and the internal main switch and synchronous

switch gate charge currents. The gate charge current

results from switching the gate capacitance of the

internal power MOSFET switches. Each time the gate

is switched from high to low to high again, a packet of

To avoid the LTC3406AB-2 from exceeding the maximum

junctiontemperature,theuserwillneedtodosomethermal

analysis. The goal of the thermal analysis is to determine

whether the power dissipated exceeds the maximum

junction temperature of the part. The temperature rise is

given by:

charge, dQ, moves from V to ground. The resulting

IN

dQ/dt is the current out of V that is typically larger

IN

than the DC bias current. In continuous mode, I

GATECHG

= f(Q + Q ) where Q and Q are the gate charges of

T

B

T

B

the internal top and bottom switches. Both the DC bias

T = (P )(θ )

R

D

JA

and gate charge losses are proportional to V and thus

IN

where P is the power dissipated by the regulator and θ

their effects will be more pronounced at higher supply

D

JA

is the thermal resistance from the junction of the die to

voltages.

the ambient temperature.

3406ab2fa

11

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LTC3406AB-2

applicaTions inForMaTion

The junction temperature, T , is given by:

A second, more severe transient is caused by switching

in loads with large (>1µF) supply bypass capacitors. The

discharged bypass capacitors are effectively put in paral-

J

T = T + T

R

J

A

where T is the ambient temperature.

A

lel with C , causing a rapid drop in V . No regulator

OUT

can deliver enough current to prevent this problem if the

load switch resistance is low and it is driven quickly. The

only solution is to limit the rise time of the switch drive

so that the load rise time is limited to approximately

As an example, consider the LTC3406AB-2 in dropout

at an input voltage of 2.7V, a load current of 600mA and

an ambient temperature of 70°C. From the typical per-

formance graph of switch resistance, the R

of the

DS(ON)

(25 • C

). Thus, a 10µF capacitor charging to 3.3V

P-channel switch at 70°C is approximately 0.27W. There-

fore, power dissipated by the part is:

LOAD

would require a 250µs rise time, limiting the charging

current to about 130mA.

2

P = I

D

• R

= 97.2mW

LOAD

DS(ON)

PC Board Layout Checklist

For the SOT-23 package, the θ is 250°C/W. Thus, the

JA

junction temperature of the regulator is:

When laying out the printed circuit board, the following

checklist should be used to ensure proper operation of the

LTC3406AB-2. Theseitemsarealsoillustratedgraphically

in Figures 3 and 4. Check the following in your layout:

T = 70°C + (0.0972)(250) = 94.3°C

J

which is below the maximum junction temperature of

125°C.

1. The power traces, consisting of the GND trace, the SW

Note that at higher supply voltages, the junction tempera-

trace, the V

trace, and the V trace should be kept

OUT

IN

ture is lower due to reduced switch resistance (R

).

DS(ON)

short, direct and wide.

Checking Transient Response

2. Does the V pin connect directly to the feedback

FB

resistors? The resistive divider R1/R2 must be

The regulator loop response can be checked by looking

at the load transient response. Switching regulators take

several cycles to respond to a step in load current. When

connected between the (+) plate of C

and ground.

OUT

3. Does C connect to V as closely as possible? This

IN

a load step occurs, V

immediately shifts by an amount

capacitor provides the AC current to the internal power

OUT

equal to (DI

• ESR), where ESR is the effective series

MOSFETs.

LOAD

resistance of C . DI

also begins to charge or dis-

OUT

LOAD

4. Keep the switching node, SW, away from the sensitive

chargeC , whichgeneratesafeedbackerrorsignal. The

OUT

V

FB

node.

regulator loop then acts to return V

value. During this recovery time V

to its steady-state

can be monitored

OUT

5. Keep the (–) plates of C , C

and the IC ground as

IN OUT

close as possible.

for overshoot or ringing that would indicate a stability

problem. For a detailed explanation of switching control

loop theory, see Application Note 76.

3406ab2fa

12

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LTC3406AB-2

applicaTions inForMaTion

1

2

3

5

4

RUN

V

FB

LTC3406AB-2

GND

R2

R1

–

C

V

OUT

L1

OUT

C

FWD

SW

V

IN

+

C

IN

+

V

IN

–

3406AB2 F03

BOLD LINES INDICATE HIGH CURRENT PATHS

Figure 3. LTC3406AB-2 Layout Diagram

V

IN

VIA TO V

R1

IN

VIA TO V

OUT

R2

PIN 1

C

FWD

LTC3406AB-2

V

OUT

SW

L1

C

IN

OUT

GND

3406AB2 F04

Figure 4. LTC3406AB-2 Suggested Layout

Design Example

Substituting V

= 2.5V, V = 4.2V, ∆I = 240mA and

OUT

IN

L

f = 2.25MHz in Equation (3) gives:

As a design example, assume the LTC3406AB-2 is used

in a single lithium-ion battery-powered cellular phone

application. The V will be operating from a maximum of

4.2V down to about 2.7V. The load current requirement

is a maximum of 0.6A but most of the time it will be in

standby mode, requiring only 2mA. Efficiency at both

low and high load currents is important. Output voltage

is 2.5V. With this information we can calculate L using

Equation (1),

2.5V

2.25MHz(240mA)

2.5V

4.2V





L =

1−

= 1.87µH









IN

A 2.2µH inductor works well for this application. For best

efficiency choose a 720mA or greater inductor with less

than 0.2W series resistance.

C will require an RMS current rating of at least 0.3A ≅

IN

I

/2 at temperature and C

will require an ESR

LOAD(MAX)

OUT













1

f DI

(

V_OUT

of less than 0.25W. In most cases, a ceramic capacitor

will satisfy this requirement.

L =

V_OUT1−

V

( )

)

L

IN

(3)

3406ab2fa

13

For more information www.linear.com/LTC3406AB-2

LTC3406AB-2

applicaTions inForMaTion

For the feedback resistors, choose R1 = 309k. R2 can

then be calculated from Equation (2) to be:

Figure 5 shows the complete circuit along with its ef-

ficiency curve.

100

V

0.6

V

= 2.5V





OUT

90

80

70

60

50

40

30

20

10

0

R2=

− 1 R1= 978k









Use a 976k 1% resistor.

2.2µH*

22pF

V

OUT

2.5V

V

IN

V

SW

IN

†

C

600mA

IN

V

= 2.7V

= 3.6V

= 4.2V

IN

C

10µF

CER

**

4.7µF

CER

OUT

LTC3406AB-2

RUN

GND

V

FB

0.1

1

10

100

1000

976k

309k

*MURATA LQH32CN2R2M33

**TAIYO YUDEN JMK316BJ106ML

^†TAIYO YUDEN JMK212BJ475MG

OUTPUT CURRENT (mA)

3406AB2 F05b

3406AB2 F05a

Figure 5a

Figure 5b. Efficiency vs Load Current

Load Step

V

OUT

200mV/DIV

OUT

100mV/DIV

I

L

500mA/DIV

I

LOAD

500mA/DIV

LOAD

500mA/DIV

3406AB2 TA02

3406AB2 TA03

V

= 3.6V

V

= 3.6V

IN

20µs/DIV

IN

V

= 2.5V

OUT

I

= 0mA TO 600mA

I

LOAD

= 50mA TO 600mA

LOAD

Load Step

V

OUT

100mV/DIV

OUT

100mV/DIV

I

L

500mA/DIV

I

LOAD

500mA/DIV

LOAD

500mA/DIV

3406AB2 TA04

3406AB2 TA05

V

= 3.6V

V

= 3.6V

IN

20µs/DIV

IN

V

= 2.5V

OUT

I

= 100mA TO 600mA

I

LOAD

= 200mA TO 600mA

LOAD

3406ab2fa

14

For more information www.linear.com/LTC3406AB-2

LTC3406AB-2

Typical applicaTions

Efficiency vs Load Current

Single Li-Ion 1.2V/600mA Regulator for

High Efficiency and Small Footprint

100

90

80

70

60

50

40

30

20

10

0

V

= 1.2V

OUT

2.2µH*

V

OUT

V

IN

V

SW

1.2V

IN

†

22pF

C

600mA

IN

C

10µF

CER

**

4.7µF

CER

OUT

LTC3406AB-2

RUN

GND

V

FB

309k

*MURATA LQH32CN2R2M33

**TAIYO YUDEN JMK316BJ106ML

^†TAIYO YUDEN JMK212BJ475MG

309k

3406AB2 TA06

V

= 2.7V

= 3.6V

= 4.2V

IN

0.1

1

10

100

1000

OUTPUT CURRENT (mA)

3406AB2 TA07

Load Step

V

OUT

200mV/DIV

OUT

100mV/DIV

I

L

500mA/DIV

I

LOAD

500mA/DIV

LOAD

500mA/DIV

3406AB2 TA08

3406AB2 TA09

V

LOAD

= 3.6V

V

= 3.6V

IN

20µs/DIV

IN

= 1.2V

OUT

I

= 0mA TO 600mA

I

LOAD

= 50mA TO 600mA

Load Step

V

OUT

100mV/DIV

OUT

100mV/DIV

I

L

500mA/DIV

I

LOAD

500mA/DIV

LOAD

500mA/DIV

3406AB2 TA10

3406AB2 TA11

V

LOAD

= 3.6V

V

= 3.6V

IN

20µs/DIV

IN

= 1.2V

OUT

I

= 100mA TO 600mA

I

LOAD

= 200mA TO 600mA

3406ab2fa

15

For more information www.linear.com/LTC3406AB-2

LTC3406AB-2

packaGe DescripTion

S5 Package

5-Lead Plastic TSOT-23

(Reference LTC DWG # 05-08-1635)

0.62

MAX

0.95

REF

2.90 BSC

(NOTE 4)

1.22 REF

1.50 – 1.75

(NOTE 4)

2.80 BSC

1.4 MIN

3.85 MAX 2.62 REF

PIN ONE

RECOMMENDED SOLDER PAD LAYOUT

PER IPC CALCULATOR

0.30 – 0.45 TYP

5 PLCS (NOTE 3)

0.95 BSC

0.80 – 0.90

0.20 BSC

DATUM ‘A’

0.01 – 0.10

1.00 MAX

0.30 – 0.50 REF

1.90 BSC

0.09 – 0.20

(NOTE 3)

NOTE:

S5 TSOT-23 0302

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

3406ab2fa

16

For more information www.linear.com/LTC3406AB-2

LTC3406AB-2

revision hisTory

REV DATE

DESCRIPTION

PAGE NUMBER

A

09/15 Revised package drawing.

16

3406ab2fa

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 representa-

tion that the interconnection of its circuits as described herein will not infringe on existing patent rights.

For more information www.linear.com/LTC3406AB-2

17

LTC3406AB-2

relaTeD parTs

PART NUMBER

DESCRIPTION

COMMENTS

LTC3406A/LTC3406AB 600mA (I ), 1.5MHz, Synchronous Step-Down

96% Efficiency, V : 2.5V to 5.5V, V

= 0.6V, I = 16µA,

OUT

IN

OUT(MIN)

Q

DC/DC Converters

I

<1µA, ThinSOT Package

SD

LTC3407/LTC3407-2

LTC3410/LTC3410B

LTC3411

Dual 600mA/800mA (I ), 1.5MHz/2.25MHz,

95% Efficiency, V : 2.5V to 5.5V, V

SD

= 0.6V, I = 40µA,

OUT

IN

Q

Synchronous Step-Down DC/DC Converters

I

<1µA, MS10E, DFN Packages

300mA (I ), 2.25MHz, Synchronous Step-Down

95% Efficiency, V : 2.5V to 5.5V, V

SD

= 0.8V, I = 26µA,

OUT

IN

Q

DC/DC Converters

I

<1µA, SC70 Package

1.25A (I ), 4MHz, Synchronous Step-Down

95% Efficiency, V : 2.5V to 5.5V, V

<1µA, MS10, DFN Packages

SD

= 0.8V, I = 60mA,

OUT

IN

Q

DC/DC Converter

I

LTC3412

2.5A (I ), 4MHz, Synchronous Step-Down

95% Efficiency, V : 2.5V to 5.5V, V

SD

= 0.8V, I = 60µA,

OUT

IN

Q

DC/DC Converter

I

<1µA, TSSOP-16E Package

LTC3440

600mA (I ), 2MHz, Synchronous Buck-Boost

95% Efficiency, V : 2.5V to 5.5V, V

SD

: 2.5V to 5.5V, I = 25µA,

OUT

IN

Q

DC/DC Converter

I

<1µA, MS10, DFN Packages

LTC3530

600mA (I ), 2MHz, Synchronous Buck-Boost

95% Efficiency, V : 1.8V to 5.5V, V

SD

: 1.8V to 5.25V, I = 40µA,

OUT

IN

Q

DC/DC Converter

I

<1µA, MS10, DFN Packages

LTC3531/LTC3531-3/

LTC3531-3.3

200mA (I ), 1.5MHz, Synchronous Buck-Boost

95% Efficiency, V : 1.8V to 5.5V, V

SD

: 2V to 5V, I = 16µA,

OUT

IN

Q

DC/DC Converters

I

<1µA, ThinSOT, DFN Packages

LTC3532

500mA (I ), 2MHz, Synchronous Buck-Boost

95% Efficiency, V : 2.4V to 5.5V, V

SD

: 2.4V to 5.25V, I = 35µA,

OUT

IN

Q

DC/DC Converter

I

<1µA, MS10, DFN Packages

LTC3542

500mA (I ), 2.25MHz, Synchronous Step-Down

95% Efficiency, V : 2.5V to 5.5V, V

SD

= 0.6V, I = 26µA,

OUT

IN

Q

DC/DC Converter

I

<1µA, 2mm × 2mm DFN Package

LTC3544/LTC3544B

LTC3547/LTC3547B

Quad 300mA + 2 x 200mA + 100mA 2.25MHz,

Synchronous Step-Down DC/DC Converters

95% Efficiency, V : 2.5V to 5.5V, V

SD

= 0.8V, I = 70µA,

Q

IN

I

<1µA, 3mm × 3mm QFN Package

Dual 300mA 2.25MHz, Synchronous Step-Down

DC/DC Converters

96% Efficiency, V : 2.5V to 5.5V, V

SD

= 0.6V, I = 40µA,

IN

Q

I

<1µA, 2mm × 3mm DFN Package

LTC3548/LTC3548-1/

LTC3548-2

Dual 400mA and 800mA (I ), 2.25MHz,

95% Efficiency, V : 2.5V to 5.5V, V

SD

= 0.6V, I = 40µA,

OUT

IN

Q

Synchronous Step-Down DC/DC Converters

I

<1µA, MS10E, DFN Packages

LTC3560

800mA (I ), 2.25MHz, Synchronous Step-Down

95% Efficiency, V : 2.5V to 5.5V, V

SD

= 0.6V, I = 16µA,

OUT

IN

Q

DC/DC Converter

I

<1µA, ThinSOT Package

LTC3561

1.25A (I ), 4MHz, Synchronous Step-Down

95% Efficiency, V : 2.5V to 5.5V, V

= 0.8V, I = 240µA,

OUT

IN

Q

DC/DC Converter

I

<1µA, DFN Package

SD

3406ab2fa

LT 0915 REV A • PRINTED IN USA

LinearTechnology Corporation

1630 McCarthy Blvd., Milpitas, CA 95035-7417

18

For more information www.linear.com/LTC3406AB-2

(408)432-1900 FAX: (408) 434-0507 www.linear.com/LTC3406AB-2

●

 LINEAR TECHNOLOGY CORPORATION 2007


型号：	LTC3406ABES5-2#TRPBF
厂家：	Linear
描述：	LTC3406AB-2 - 2.25MHz, 600mA Synchronous Step-Down Regulator in ThinSOT; Package: SOT; Pins: 5; Temperature Range: -40°C to 85°C 开关光电二极管
文件：	总18页 (文件大小：345K)
中文：	中文翻译
下载：	下载PDF数据表文档文件

LTC3406ABES5-2#TRPBF [Linear]

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