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LTC3406AB中文资料

3406abfa

TYPICAL APPLICATION

FEATURES

APPLICATIONS

DESCRIPTION

Synchronous Step-Down

Regulator in ThinSOT

The LTC ?3406AB is a high ef? ciency monolithic synchro-nous buck regulator using a constant frequency, current mode architecture. Supply current with no load is 200μA, dropping to <1μA in shutdown. The 2.5V to 5.5V input voltage range makes the LTC3406AB ideally suited for single Li-Ion battery-powered applications. 100% duty cycle provides low dropout operation, extending battery run time in portable systems. PWM pulse skipping mode operation provides very low output ripple voltage for noise sensitive applications. Refer to LTC3406A for applications that require Burst Mode ? operation.

Switching frequency is internally set at 1.5MHz, allowing the use of small surface mount inductors and capacitors. The internal synchronous switch increases ef? ciency and eliminates the need for an external Schottky diode. Low output voltages are easily supported with the 0.6V feedback reference voltage. The LTC3406AB is available in a low pro? le (1mm) ThinSOT package.

Ef? ciency vs Load Current

■

High Ef? ciency: Up to 96%■ 600mA Output Current

■ 2.5V to 5.5V Input Voltage Range

■ 1.5MHz Constant Frequency Operation ■ No Schottky Diode Required

■ Low Dropout Operation: 100% Duty Cycle ■ Low Quiescent Current: 200μA ■ ±2% 0.6V Reference

■ Shutdown Mode Draws <1μA Supply Current ■ Internal Soft-Start Limits Inrush Current

■ Current Mode Operation for Excellent Line and Load Transient Response ■

Overtemperature Protected ■ Low Pro? le (1mm) ThinSOT TM Package

■

Cellular Telephones

■ Satellite and GPS Receivers ■ Wireless and DSL Modems ■ Digital Still Cameras ■ Media Players

■

Portable Instruments

All other trademarks are the property of their respective owners.Protected by U.S. Patents including 5481178, 6580258.

V OUT

OUTPUT CURRENT (mA)

0.1

E F F I C I E N C Y (%)

1000

100

9080706050403020103406B TA14

100

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PIN CONFIGURATION

ABSOLUTE MAXIMUM RATINGS

Input Supply Voltage ....................................–0.3V to 6V RUN, V FB Voltages .......................................–0.3V to V IN SW Voltage (DC) ...........................–0.3V to (V IN + 0.3V)P-Channel Switch Source Current (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 Junction Temperature (Notes 3, 6) .......................125°C Storage Temperature Range ...................–65°C to 150°C Lead Temperature (Soldering, 10 sec) ..................300°C

(Note 1)

RUN 1GND 2SW 3

5 V FB

4 V IN TOP VIEW

S5 PACKAGE

5-LEAD PLASTIC TSOT-23

T JMAX = 125°C, θJA = 250°C/W, θJC = 90°C/W

ORDER INFORMATION

ELECTRICAL CHARACTERISTICS SYMBOL PARAMETER CONDITIONS

MIN

TYP MAX UNITS I VFB Feedback Current ●

±30nA V FB Regulated Feedback Voltage (Note 4)

●0.58800.60.6120V ΔV FB Reference Voltage Line Regulation V IN = 2.5V to 5.5V (Note 4)●

0.040.4%/V I PK Peak Inductor Current V IN = 3V, V FB = 0.5V Duty Cycle < 35%

0.75

1 1.25

A V LOADREG Output Voltage Load Regulation 0.5

V IN Input Voltage Range ●

2.5

5.5V I S

Input DC Bias Current

Active Mode Shutdown (Note 5)V FB = 0.63V

V RUN = 0V, V IN = 5.5V 2000.1

3001μA μA f OSC Oscillator Frequency V FB = 0.6V ● 1.2

1.5 1.8MHz R PFET R DS(ON) of P-Channel FET I SW = 100mA 0.230.35ΩR NFET R DS(ON) of N-Channel FET I SW = –100mA

0.210.35ΩI LSW SW Leakage V RUN = 0V, V SW = 0V or 5V, V IN = 5V ±0.01±1μA t SOFTSTART

Soft-Start Time

V FB from 10% to 90% Full-scale

0.6

0.9

1.2

The ● denotes the speci? cations which apply over the full operating

temperature range, otherwise speci? cations are at T A = 25°C. V IN = 3.6V unless otherwise speci? ed.

LEAD FREE FINISH TAPE AND REEL PART MARKING PACKAGE DESCRIPTION TEMPERATURE RANGE LTC3406ABES5#PBF

LTC3406ABES5#TRPBF

LTCXZ

5-Lead Plastic TSOT-23

–40°C to 85°C

Consult LTC Marketing for parts speci? ed with wider operating temperature ranges.Consult LTC Marketing for information on non-standard lead based ? nish parts.

For more information on lead free part marking, go to: https://www.wendangku.net/doc/ca1663723.html,/leadfree/ For more information on tape and reel speci? cations, go to: https://www.wendangku.net/doc/ca1663723.html,/tapeandreel/

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INPUT VOLTAGE (V)

E F F I C I E N C Y (%)

3406B G01

5100908070

6050403020100

ELECTRICAL CHARACTERISTICS 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 2: The LTC3406ABE is guaranteed to meet performance speci? cations from 0°C to 85°C. Speci? cations over the –40°C to 85°C operating temperature range are assured by design, characterization and correlation with statistical process controls.

Note 3: T J is calculated from the ambient temperature T A and power dissipation P D according to the following formula: LTC3406AB: T J = T A + (P D )(250°C/W)

The ● denotes the speci? cations which apply over the full operating

temperature range, otherwise speci? cations are at T A = 25°C. V IN = 3.6V unless otherwise speci?

ed.SYMBOL PARAMETER CONDITIONS

MIN TYP MAX UNITS

V RUN RUN Threshold ●0.3

1 1.5V I RUN

RUN Leakage Current

●

±0.01

±1

μA

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

V FB to the output of the error ampli?

er.Note 5: Dynamic supply current is higher due to the gate charge being delivered at the switching frequency.

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 speci? ed maximum operating junction temperature may impair device reliability.

Note7: Limited by long term current density considerations.

Ef? ciency vs Input Voltage

Ef? ciency vs Load Current

Reference Voltage vs Temperature

TYPICAL PERFORMANCE CHARACTERISTICS

(From Front Page Figure Except for the Resistive Divider Resistor Values)

OUTPUT CURRENT (mA)

0.1

E F F I C I E N C Y (%)

1000

10090807060504030201003406B G02

1100

OUTPUT CURRENT (mA)

0.1

E F F I C I E N C Y (%)

1000

10090807060504030201003406B G03

100TEMPERATURE (°C)

–50R E F E R E N C E V O L T A G E (V )

0.6050.6100.61525753406AB G21

0.6000.595–25

50100125

0.590

0.585

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OUTPUT CURRENT (mA)

1.780

O U T P U T V O L T A G E (V )

1.7881.7961.804200

400

3406B G24

1.8121.8201.7841.7921.8001.8081.816600

Oscillator Frequency vs Temperature

Oscillator Frequency vs Supply Voltage

Output vs Load Current

R DS(ON) vs Input Voltage

Dynamic Supply Current

Dynamic Supply Current vs Temperature

Switch Leakage vs Temperature

Switch Leakage vs Input Voltage

TYPICAL PERFORMANCE CHARACTERISTICS

(From Front Page Figure Except for the Resistive Divider Resistor Values)

TEMPERATURE (°C)

–501.30

O S C I L L A T O R F R E Q U E N C Y (M H z )1.351.401.451.601.5005075

3406B G22

1.55–25

25100

125

INPUT VOLTAGE (V)

2.0

O S C I L L A T O R F R E Q U E N C Y (M H z )

1.601.55

1.501.451.401.351.301.25

1.20

3.0

4.0

5.0

2.5

3.5

4.5

5.5

6.0

3406B G07

INPUT VOLTAGE (V)

R D S (0N ) (Ω)0.30

0.350.40353406B G250.250.201

0.15

0.10

TEMPERATURE (°C)

–50R D S (O N ) (Ω)

0.3525

3406B G260.200.10–25

500.05

0.400.300.250.1575100

125

INPUT VOLTAGE (V)

D Y N A M I C S U P P L Y C U R R E

N T (μA )501001502003

3406B G27

250300

2.5

3.5

4.5

5.5TEMPERATURE (°C)

–50D Y N A M I C S U P P L Y C U R

R E N T (μA )

20025030025753406B G2*******–25

50100125

500

TEMPERATURE (°C)

–508010014025753406B G29

6040–25

50100

125

120S W I T C H L E A K A G E (n A )

INPUT VOLTAGE (V)

S W I T C H L E A K A G E (p A )

2004006001

343406B G30

58001000

100

3005007009006

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PIN FUNCTIONS

RUN (P in 1): Run Control Input. F orcing 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 ? oating.GND (Pin 2): Ground Pin.

SW (Pin 3): Switch Node Connection to Inductor. This pin connects to the drains of the internal main and synchronous power MOSFET switches.

V IN (Pin 4): Main Supply Pin. Must be closely decoupled to GND, Pin 2, with a 2.2μF or greater ceramic capacitor.V FB (Pin 5): Feedback Pin. Receives the feedback voltage from an external resistive divider across the output.

TYPICAL PERFORMANCE CHARACTERISTICS

(From Front Page Figure Except for the Resistive Divider Resistor Values)

Start-Up from Shutdown

Load Step

Load Step Discontinuous Operation

RUN 2V/DIV V OUT 1V/DIV I LOAD 500mA/DIV

400μs/DIV V IN = 3.6V V OUT = 1.8V

I LOAD

= 600mA (3Ω RES)

3406B G31

V OUT 200mV/DIV

I L

500mA/DIV

I LOAD 500mA/DIV

20μs/DIV V IN = 3.6V V OUT = 1.8V

I LOAD = 0mA TO 600mA

3406B G32

V OUT 200mV/DIV

I L

500mA/DIV

I LOAD 500mA/DIV

20μs/DIV

IN = 3.6V V OUT = 1.8V

I LOAD = 50mA TO 600mA

3406B G33

V OUT 200mV/DIV

I L

500mA/DIV I LOAD 500mA/DIV

20μs/DIV V IN = 3.6V V OUT = 1.8V

I LOAD = 100mA TO 600mA

3406B G34

V OUT 200mV/DIV

I L

500mA/DIV

I LOAD 500mA/DIV

μs/DIV V

IN = 3.6V V OUT = 1.8V

I LOAD = 200mA TO 600mA

3406B G35

V OUT 20mV/DIV AC COUPLED

SW (2V/DIV)

I L

200mA/DIV

500ns/DIV

V IN = 3.6V V OUT = 1.8V I LOAD = 25mA

3406B G36

FUNCTIONAL DIAGRAM

+–

–

OPERATION(Refer to Functional Diagram)

Main Control Loop

The LTC3406AB uses a constant frequency, current mode step-down architecture. Both the main (P-channel MOSF ET) and synchronous (N-channel MOSF ET) switches are internal. During normal operation, the internal top power MOSFET is turned on each cycle when the oscillator sets the RS latch, and turned off when the current comparator, I COMP, resets the RS latch. The peak inductor current at which I COMP resets the RS latch, is controlled by the output of error ampli? er EA. When the load current increases, it causes a slight decrease in the feedback voltage, FB, relative to the 0.6V reference, which in turn, causes the EA ampli? er’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 by the current reversal comparator I RCMP, or the beginning of the next clock cycle.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.

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 RCMP, and the switch voltage will ring. This is discontinuous mode operation, and is normal behavior for the switching regulator. At very light loads, the LTC3406AB will automatically skip pulses in pulse skipping mode operation to maintain output regulation. Refer to the LTC3406A data sheet if Burst Mode operation is preferred.

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Dropout Operation

As the input supply voltage decreases to a value approach-ing the output voltage, the duty cycle increases toward the maximum on-time. Further reduction of the supply voltage forces the main switch to remain on for more than one cycle until it reaches 100% duty cycle. The output voltage will then be determined by the input voltage minus the voltage drop across the P-channel MOSFET and the inductor.

An important detail to remember is that at low input supply voltages, the R DS(ON) of the P-channel switch increases (see Typical Performance Characteristics). Therefore, the user should calculate the power dissipation when the LTC3406AB is used at 100% duty cycle with low input voltage (See Thermal Considerations in the Applications Information section).Slope Compensation and Inductor Peak Current Slope compensation provides stability in constant fre-quency architectures by preventing subharmonic oscilla-tions 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 uses a patented scheme that counteracts this compensating ramp, which allows the maximum inductor peak current to remain unaffected throughout all duty cycles.

OPERATION(Refer to Functional Diagram)

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The basic LTC3406AB application circuit is shown on the front page. External component selection is driven by the load requirement and begins with the selection of L fol-lowed by C IN and C OUT .Inductor Selection

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 currents. Higher V IN or V OUT also increases the ripple cur-rent as shown in equation 1. A reasonable starting point for setting ripple current is ΔI L = 240mA (40% of 600mA).

Δ=()()?

??????I f L V V V L OUT OUT IN 1

1 (1)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 ef? ciency, choose a low DC-resistance inductor.Inductor Core Selection

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 size requirements and any radiated ? eld/EMI require-ments than on what the LTC3406AB requires to operate.Table 1 shows some typical surface mount inductors that work well in LTC3406AB applications.

APPLICATIONS INFORMATION

C IN and C OUT Selection

In continuous mode, the source current of the top MOSFET is a square wave of duty cycle V OUT /V IN . To prevent large voltage transients, a low ESR input capacitor sized for the maximum RMS current must be used. The maximum RMS capacitor current is given by:

C I V V V IN OMAX

OUT IN OUT required I RMS ??()????

1/22

V IN

This formula has a maximum at V IN = 2V OUT , where I RMS = I OUT /2. This simple worst-case condition is commonly used for design because even signi? cant de-viations do not offer much relief. Note that the capacitor manufacturer’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 OUT is driven by the required effective series resistance (ESR).

Table 1. Representative Surface Mount Inductors

PART NUMBER VALUE (μH)DCR (Ω MAX)MAX DC CURRENT (A)

SIZE

W × L × H (mm 3)Sumida CDRH3D16

1.5

2.2

3.3

4.70.0430.0750.1100.162 1.551.201.100.90 3.8 × 3.8 × 1.8

Sumida CMD4D06 2.23.34.70.1160.1740.2160.9500.7700.750 3.5 × 4.3 × 0.8

Panasonic ELT5KT 3.34.70.170.20 1.000.95 4.5 × 5.4 × 1.2Murata LQH32CN

1.02.24.7

0.0600.0970.150

1.000.790.65

2.5 ×

3.2 × 2.0

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Typically, once the ESR requirement for C OUT has been met, the RMS current rating generally far exceeds the I RIPPLE(P-P) requirement. The output ripple ΔV OUT is determined by:

Δ?Δ+

????

?V I ESR fC OUT L OUT 1

8where f = operating frequency, C OUT = output capacitance

and ΔI L = ripple current in the inductor. For a ?

xed output voltage, the output ripple is highest at maximum input voltage since ΔI L increases with input voltage.

Aluminum electrolytic and dry tantalum capacitors are both

available in surface mount con? gurations. 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 speci? c https://www.wendangku.net/doc/ca1663723.html,ing Ceramic Input and Output Capacitors

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’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.

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

ringing can couple to the output and be mistaken as loop instability. At worst, a sudden inrush of current through the long wires can potentially cause a voltage spike at V IN , large enough to damage the part.

When choosing the input and output ceramic capacitors, choose the X5R or X7R dielectric formulations. These dielectrics have the best temperature and voltage charac-teristics of all the ceramics for a given value and size.Output Voltage Programming

In the adjustable version, the output voltage is set by a resistive divider according to the following formula: V V R R OUT =+????

06121. (2)

The external resistive divider is connected to the output, allowing remote voltage sensing as shown in Figure 1.

APPLICATIONS INFORMATION

0.6V ≤ V OUT ≤ 5.5V

Figure 1. Setting the LTC3406AB Output Voltage

Ef? ciency Considerations

The ef? ciency of a switching regulator is equal to the output power divided by the input power times 100%. It is often useful to analyze individual losses to determine what is limiting the ef? ciency and which change would produce the most improvement. Ef? ciency can be expressed as: Ef? ciency = 100% – (L1 + L2 + L3 + ...)

where L1, L2, etc. are the individual losses as a percent-age of input power.

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Although all dissipative elements in the circuit produce losses, two main sources usually account for most of the losses in LTC3406AB circuits: V IN quiescent current and I 2R losses. The V IN quiescent current loss dominates the ef? ciency loss at very low load currents whereas the

I 2R loss dominates the ef?

ciency loss at medium to high load currents. In a typical ef? ciency plot, the ef? ciency curve at very low load currents can be misleading since the actual power lost is of no consequence as illustrated in Figure 2.

2. I 2R losses are calculated from the resistances of the internal switches, R SW , and external inductor R L . In continuous mode, the average output current ? owing 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 DS(ON) and the duty cycle (DC) as follows: R SW = (R DS(ON)TOP )(DC) + (R DS(ON)BOT )(1 – DC) The R DS(ON) for both the top and bottom MOSF ETs can be obtained from the Typical Performance Characteristics curves. Thus, to obtain I 2R losses, simply add R SW to R L and multiply the result by the square of the average output current.

Other losses including C IN and C OUT ESR dissipative losses and inductor core losses generally account for less than 2% total additional loss.Thermal Considerations

In most applications the LTC3406AB does not dissipate much heat due to its high ef? ciency. But, in applications where the LTC3406AB 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 maximum junction temperature of the part. If the junction temperature reaches approximately 150°C, both power switches will be turned off and the SW node will become high impedance.

To avoid the LTC3406AB from exceeding the maximum junction temperature, the user will need to do some thermal 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: T R = (P D )(θJA )

where P D is the power dissipated by the regulator and θJA is the thermal resistance from the junction of the die to the ambient temperature.

APPLICATIONS INFORMATION

Figure 2. Power Lost vs Load Current

1. The V IN quiescent current is due to two components: 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 charge, dQ, moves from V IN to ground. The resulting dQ/dt is the current out of V IN that is typically larger than the DC bias current. In continuous mode, I GATECHG = f(Q T + Q B ) where Q T and Q B are the gate charges of the internal top and bottom switches. Both the DC bias and gate charge losses are proportional to V IN and thus their effects will be more pronounced at higher supply voltages.

OUTPUT CURRENT (mA)

0.01

0.001

P O W E R L O S S (W )

0.10.1

10.0100.01000.0

3406B F08

0.0001

1.0

The junction temperature, T J, is given by:

T J = T A + T R

where T A is the ambient temperature.

As an example, consider the LTC3406AB 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 DS(ON) of the P-channel switch at 70°C is approximately 0.27Ω. There-fore, power dissipated by the part is:

P D = I LOAD2 ? R DS(ON) = 97.2mW

For the SOT-23 package, the θJA is 250°C/W. Thus, the junction temperature of the regulator is:

T J = 70°C + (0.0972)(250) = 94.3°C

which is below the maximum junction temperature of 125°C.

Note that at higher supply voltages, the junction temperature is lower due to reduced switch resistance (R DS(ON)). Checking Transient Response

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 a load step occurs, V OUT immediately shifts by an amount equal to (ΔI LOAD ? ESR), where ESR is the effective series resistance of C OUT. ΔI LOAD also begins to charge or dis-charge C OUT, which generates a feedback error signal. The regulator loop then acts to return V OUT to its steady-state value. During this recovery time V OUT can be monitored for overshoot or ringing that would indicate a stability problem. For a detailed explanation of switching control loop theory, see Application Note 76. 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-lel with C OUT, causing a rapid drop in V OUT. No regulator 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 (25 ? C LOAD). Thus, a 10μF capacitor charging to 3.3V would require a 250μs rise time, limiting the charging current to about 130mA.

PC Board Layout Checklist

When laying out the printed circuit board, the following checklist should be used to ensure proper operation of the LTC3406AB. These items are also illustrated graphically in Figures 3 and 4. Check the following in your layout:

1. The power traces, consisting of the GND trace, the SW trace, the V OUT trace and the V IN trace should be kept short, direct and wide.

2. Does the V FB pin connect directly to the feedback resistors? The resistive divider R1/R2 must be connected between the (+) plate of C OUT and ground.

3. Does C IN connect to V IN as closely aspossible? This capacitor provides the AC current to the internal power MOS

ETs.

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

5. Keep the (–) plates of C IN and C OUT and the IC ground, as close as possible.

APPLICATIONS INFORMATION

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Design Example

As a design example, assume the LTC3406AB is used in a single lithium-ion battery-powered cellular phone application. The V IN 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. Ef? ciency at both low and high load currents is important. Output voltage is 2.5V. With this information we can calculate L using Equation (1),

L f I V V V L OUT OUT IN =()Δ()???

????

1 (3)

Substituting V OUT = 2.5V, V IN = 4.2V, ΔI L = 240mA and

f = 1.5MHz in Equation (3) gives:

L V MHz mA V V H =?????

?=μ251524012542281..()...A 2.2μH inductor works well for this application. For best

ef? ciency choose a 720mA or greater inductor with less than 0.2Ω series resistance.

C IN will require an RMS current rating of at least 0.3A ? I LOAD(MAX)/2 at temperature and C OUT will require an ESR of less than 0.25Ω. In most cases, a ceramic capacitor will satisfy this requirement.

Figure 3. LTC3406AB Layout Diagram

Figure 4. LTC3406AB Suggested Layout

APPLICATIONS INFORMATION

BOLD LINES INDICATE HIGH CURRENT PATHS

3406AB F06a

OUT

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APPLICATIONS INFORMATION

For the feedback resistors, choose R1 = 316k. R2 can then be calculated from Equation (2) to be: R V R k

OUT 206111000=?????

?=. (4)

F igure 5 shows the complete circuit along with its ef-? ciency curve.

Figure 5

OUTPUT CURRENT (mA)

0.1

E F F I C I E N C Y (%)

1000

10090

807060504030201003406B G03

1100

V OUT 200mV/DIV

I L

500mA/DIV I LOAD 500mA/DIV

20μs/DIV V IN = 3.6V V OUT = 2.5V

I LOAD = 200mA TO 450mA

3406B F10

Load Step

OUT V OUT 100mV/DIV

I L

500mA/DIV

I LOAD 500mA/DIV

20μs/DIV V IN = 3.6V V OUT = 2.5V

I LOAD = 300mA TO 600mA

3406B F16

Load Step

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TYPICAL APPLICATIONS

Single Li-Ion 1.2V/600mA Regulator for High Ef? ciency and Small Footprint

OUTPUT CURRENT (mA)

0.1

E F F I C I E N C Y (%)

1000

100

9080706050403020100

3406B G02

1100

Ef? ciency vs Load Current

V OUT 200mV/DIV

I L

500mA/DIV I LOAD 500mA/DIV

20μs/DIV V IN = 3.6V V OUT = 1.2V

I LOAD = 200mA TO 500mA

3406B F12

Load Step

OUT V OUT 100mV/DIV

I L

500mA/DIV

I LOAD 500mA/DIV

20μs/DIV V IN = 3.6V V OUT = 1.2V

I LOAD = 300mA TO 600mA

3406B F14

Load Step

3406abfa

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.

PACKAGE DESCRIPTION

S5 Package

5-Lead Plastic SOT-23

(Reference LTC DWG # 05-08-1633 Rev B)

(NOTE 3)

S5 TSOT-23 0302 REV B

NOTE:

1. DIMENSIONS ARE IN MILLIMETERS

2. DRAWING NOT TO SCALE

3. DIMENSIONS ARE INCLUSIVE OF PLATING

4. DIMENSIONS ARE EXCLUSIVE OF MOLD FLASH AND METAL BURR

5. MOLD FLASH SHALL NOT EXCEED 0.254mm

6. JEDEC PACKAGE REFERENCE IS MO-193

0.620.95RECOMMENDED SOLDER PAD LAYOUT

PER IPC CALCULATOR

3406abfa

Linear Technology Corporation

1630 McCarthy Blvd., Milpitas, CA 95035-7417

(408) 432-1900 ● FAX: (408) 434-0507 ● https://www.wendangku.net/doc/ca1663723.html,

? LINEAR TECHNOLOGY CORPORA TION 2007

LT 0907 REV A ? PRINTED IN USA

RELATED PARTS

PART NUMBER DESCRIPTION

COMMENTS

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LTC3530

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LTC3532500mA (I OUT ), 2MHz, Synchronous Buck-Boost DC/DC Converter

95% Ef? ciency, V IN : 2.4V to 5.5V, V OUT(MIN) = 2.4V to 5.25V, I Q = 35μA,I SD <1μA, MS10, DFN Packages

LTC3542

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95% Ef? ciency, V IN : 2.5V to 5.5V, V OUT(MIN) = 0.6V, I Q = 26μA,I SD <1μA, 2mm × 2mm DFN Package

LTC3544/LTC3544B Quad 300mA + 2 x 200mA + 100mA 2.25MHz,Synchronous Step-Down DC/DC Converters 95% Ef? ciency, V IN : 2.5V to 5.5V, V OUT(MIN) = 0.8V, I Q = 70μA,I SD <1μA, 3mm × 3mm QFN Package

LTC3547/LTC3547B

Dual 300mA 2.25MHz, Synchronous Step-Down DC/DC Converters

96% Ef? ciency, V IN : 2.5V to 5.5V, V OUT(MIN) = 0.6V, I Q = 40μA,I SD <1μA, 2mm × 3mm DFN Package

LTC3548/LTC3548-1/LTC3548-2Dual 400mA and 800mA (I OUT ), 2.25MHz,

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LTC3561

1.25A (I OUT ), 4MHz, Synchronous Step-Down DC/DC Converter

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