LTC3406AES5#TRMPBF [Linear]
LTC3406A - 1.5MHz, 600mA Synchronous Step-Down Regulator in ThinSOT; Package: SOT; Pins: 5; Temperature Range: -40°C to 85°C;
| 型号： | LTC3406AES5#TRMPBF |
| 厂家： | 
Linear |
| 描述： | LTC3406A - 1.5MHz, 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16页 (文件大小：296K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
LTC3406A
1.5MHz, 600mA
Synchronous Step-Down
Regulator in ThinSOT
DESCRIPTION
The LTC®3406A is a high efficiency monolithic synchro-
nous buck regulator using a constant frequency, current
modearchitecture.Supplycurrentduringoperationisonly
20μA, dropping to ≤1μA in shutdown. The 2.5V to 5.5V
input voltage range makes the LTC3406A ideally suited
forsingleLi-Ionbattery-poweredapplications. 100%duty
cycle provides low dropout operation, extending battery
runtime portable systems. Automatic Burst Mode opera-
tion increases efficiency at light loads, further extending
battery runtime.
FEATURES
■
High Efficiency: Up to 96%
■
Very Low Quiescent Current: Only 20µA
Low Output Ripple Voltage During Burst Mode®
■
Operation
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
■
2% 0.6V Reference
■
Shutdown Mode Draw ≤1µA Supply Current
Switching frequency is internally set at 1.5MHz, 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 output voltages are easily supported with the 0.6V
feedback reference voltage. The LTC3406A is available in
a low profile (1mm) ThinSOT package.
■
Internal Soft-Start Limits Inrush Current
■
Current Mode Operation for Excellent Line and
Load Transient Response
■
Overtemperature Protected
Low Profile (1mm) ThinSOTTM Package
■
APPLICATIONS
, LT, LTC and LTM are registered trademarks 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.
■
Cellular Telephones
■
Wireless and DSL Modems
■
Digital Still Cameras
■
Media Players
■
Portable Instruments
■
Point of Load Regulation
TYPICAL APPLICATION
Efficiency vs Load Current
100
90
80
70
60
50
40
30
20
2.2μH
V
OUT
V
IN
1.8V
V
SW
LTC3406A
IN
22pF
600mA
4.7μF
CER
10μF
CER
RUN
GND
V
FB
619k
309k
3406A TA01
V
V
V
= 2.7V
= 3.6V
= 4.2V
IN
IN
IN
10
V
OUT
= 1.8V
1
0
0.1
10
100
1000
OUTPUT CURRENT (mA)
3406A TA01b
3406afa
1
LTC3406A
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 (DC)
S5 PACKAGE
5-LEAD PLASTIC TSOT-23
(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)
T
= 125°C, θ = 250°C/W, θ = 90°C/W
JA JC
JMAX
LTC3406AE ..............................................–40°C to 85°C
LTC3406AI .............................................–40°C to 125°C
Junction Temperature (Notes 3, 6)........................ 125°C
Storage Temperature Range...................–65°C to 150°C
Lead Temperature (Soldering, 10 sec) .................. 300°C
ORDER INFORMATION
LEAD FREE FINISH
LTC3406AES5#PBF
LTC3406AIS5#PBF
TAPE AND REEL
PART MARKING*
LTCWJ
PACKAGE DESCRIPTION
5-Lead Plastic TSOT-23
5-Lead Plastic TSOT-23
TEMPERATURE RANGE
–40°C to 85°C
LTC3406AES5#TRPBF
LTC3406AIS5#TRPBF
LTCWJ
–40°C to 125°C
Consult LTC Marketing for parts specified with wider operating temperature ranges. *Temperature grades are identified by a label on the shipping container.
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/
ELECTRICAL CHARACTERISTICS The ● denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VIN = 3.6V unless otherwise specified.
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
●
I
Feedback Current
30
nA
VFB
●
●
V
Regulated Feedback Voltage
(Note 4) LTC3406AE
(Note 4) LTC3406AI
0.5880
0.585
0.6
0.6
0.6120
0.615
V
V
FB
●
●
∆V
Reference Voltage Line Regulation
Peak Inductor Current
V
V
= 2.5V to 5.5V (Note 4) LTC3406AE
= 2.5V to 5.5V (Note 4) LTC3406AI
0.04
0.04
0.4
0.6
%/V
%/V
FB
IN
IN
I
V
IN
= 3V, V = 0.5V
0.75
2.5
1
1.25
A
PK
FB
Duty Cycle < 35%
V
V
Output Voltage Load Regulation
Input Voltage Range
0.5
%
V
LOADREG
IN
●
●
5.5
I
Input DC Bias Current
Active Mode
Sleep Mode
Shutdown
(Note 5)
S
V
V
V
= 0V
= 0.63V
200
16
0.1
300
30
1
μA
μA
μA
FB
FB
RUN
= 0V, V = 5.5V
IN
f
Oscillator Frequency
V
FB
= 0.6V
1.2
1.5
1.8
MHz
Ω
OSC
R
R
of P-Channel FET
I
SW
= 100mA
0.23
0.35
PFET
DS(ON)
3406afa
2
LTC3406A
ELECTRICAL CHARACTERISTICS
The ● denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VIN = 3.6V unless otherwise specified.
SYMBOL PARAMETER CONDITIONS
of N-Channel FET = –100mA
MIN
TYP
0.21
0.01
0.9
MAX
0.35
1
UNITS
Ω
R
NFET
R
I
SW
DS(ON)
I
t
SW Leakage
V
V
= 0V, V = 0V or 5V, V = 5V
μA
LSW
RUN
SW
IN
Soft-Start Time
RUN Threshold
RUN Leakage Current
from 10% to 90% Full-Scale
FB
0.6
0.3
1.2
1.5
1
ms
V
SOFT-START
●
●
V
1
RUN
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 LTC3406A is tested in a proprietary test mode that connects
to the output of the error amplifier.
Note 5: Dynamic supply current is higher due to the gate charge being
V
FB
delivered at the switching frequency.
Note 2: The LTC3406AE 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. The LTC3406AI is guaranteed to meet the
specified performance over the full –40°C to 125°C operating temperature
range.
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 7: Limited by long term current density considerations.
Note 3: T is calculated from the ambient temperature T and power
J
A
dissipation P according to the following formula:
D
LTC3406A: T = T + (P )(250°C/W)
J
A
D
TYPICAL PERFORMANCE CHARACTERISTICS
(From Front Page Figure Except for the Resistive Divider Resistor Values)
Efficiency vs Input Voltage
Efficiency vs Load Current
Efficiency vs Load Current
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
I
= 10mA
= 100mA
= 600mA
V
IN
V
IN
V
IN
= 2.7V
= 3.6V
= 4.2V
V
= 2.7V
= 3.6V
= 4.2V
L
IN
IN
IN
I
V
V
L
I
V
OUT
= 1.8V
3
V
OUT
= 1.2V
1
V
OUT
= 2.5V
1
L
2
4
5
6
0.1
10
100
1000
0.1
10
100
1000
OUTPUT CURRENT (mA)
OUTPUT CURRENT (mA)
INPUT VOLTAGE (V)
3406A G02
3406A G03
3406A G01
3406afa
3
LTC3406A
TYPICAL PERFORMANCE CHARACTERISTICS
(From Front Page Figure Except for the Resistive Divider Resistor Values)
Reference Voltage vs
Temperature
Efficiency vs Input Voltage
Output vs Load Current
100
90
80
70
60
50
40
30
20
10
0
1.820
1.816
0.615
0.610
0.605
0.600
V
= 1.8V
V
V
V
= 2.7V
= 3.6V
= 4.2V
OUT
V
IN
= 3.6V
IN
IN
IN
1.812
1.808
1.804
1.800
1.796
0.595
0.590
0.585
1.792
1.788
1.784
1.780
I
I
I
= 10mA
= 100mA
= 600mA
L
L
L
V
OUT
= 2.5V
3
2
4
5
6
0
400
200
OUTPUT CURRENT (mA)
600
50
TEMPERATURE (°C)
100 125
–50 –25
0
25
75
INPUT VOLTAGE (V)
3406A G05
3406A G04
3406A G06
Oscillator Frequency vs
Temperature
Oscillator Frequency vs
Input Voltage
Burst Mode
1.60
1.55
1.50
1.45
1.60
1.55
1.50
1.45
1.40
1.35
1.30
1.25
1.20
V
= 3.6V
IN
SW
2V/DIV
V
OUT
20mV/DIV
AC COUPLED
I
L
1.40
1.35
1.30
200mA/DIV
3406A G09
V
V
I
= 3.6V
4μs/DIV
IN
OUT
= 1.8V
= 10mA
LOAD
50
TEMPERATURE (°C)
100 125
4.0 4.5
–50 –25
0
25
75
2.0 2.5 3.0 3.5
5.0 5.5 6.0
Burst Mode OPERATION
INPUT VOLTAGE (V)
3406A G07
3406A G08
RDS(ON) vs Input Voltage
RDS(ON) vs Temperature
Dynamic Supply Current
0.40
0.35
0.30
0.25
0.40
10
9
8
7
6
5
4
3
2
1
0
V
LOAD
= 1.2V
= 0A
OUT
I
0.35
0.30
V
IN
= 3.6V
V
IN
= 2.7V
0.25
0.20
0.15
0.10
0.05
MAIN SWITCH
V
IN
= 4.2V
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
2.0
4.0
5.0 5.5
2.5 3.0 3.5
4.5
6.0
INPUT VOLTAGE (V)
TEMPERATURE (°C)
INPUT VOLTAGE (V)
3406A G10
3406A G11
3406A G12
3406afa
4
LTC3406A
TYPICAL PERFORMANCE CHARACTERISTICS
(From Front Page Figure Except for the Resistive Divider Resistor Values)
Dynamic Supply Current vs
Temperature
Switch Leakage vs Temperature
Switch Leakage vs Input Voltage
140
120
1000
900
800
700
600
500
400
300
200
100
0
300
250
200
150
RUN = 0V
V
V
LOAD
= 3.6V
IN
= 1.2V
= 0A
OUT
I
100
80
60
40
20
MAIN SWITCH
MAIN SWITCH
100
50
0
SYNCHRONOUS
SWITCH
SYNCHRONOUS
SWITCH
0
50
TEMPERATURE (°C)
100 125
–50 –25
0
25
75
0
1
3
4
5
6
50
TEMPERATURE (°C)
100 125
2
–50 –25
0
25
75
INPUT VOLTAGE (V)
3406A G14
3406A G15
3406A G13
Start-Up from Shutdown
Load Step
Load Step
V
OUT
200mV/DIV
V
RUN
2V/DIV
OUT
200mV/DIV
V
I
OUT
I
L
L
1V/DIV
500mA/DIV
500mA/DIV
I
I
LOAD
LOAD
I
LOAD
500mA/DIV
500mA/DIV
500mA/DIV
3406A G17
3406A G18
3406A G16
V
V
I
= 3.6V
20μs/DIV
V
V
I
= 3.6V
20μs/DIV
V
V
I
= 3.6V
500μs/DIV
IN
OUT
IN
OUT
IN
OUT
= 1.8V
= 0mA TO 600mA
= 1.8V
= 50mA TO 600mA
= 1.8V
= 600mA (3Ω RES)
LOAD
LOAD
LOAD
Load Step
Load Step
Discontinuous Operation
V
V
SW
2V/DIV
OUT
OUT
200mV/DIV
200mV/DIV
V
OUT
I
I
L
L
20mV/DIV
500mA/DIV
500mA/DIV
AC COUPLED
I
L
I
I
LOAD
LOAD
200mA/DIV
500mA/DIV
500mA/DIV
3406A G20
3406A G19
3406A G21
V
V
I
= 3.6V
20μs/DIV
V
V
I
= 3.6V
20μs/DIV
V
V
I
= 3.6V
500ns/DIV
IN
OUT
IN
OUT
IN
OUT
= 1.8V
= 200mA TO 600mA
= 1.8V
= 100mA TO 600mA
= 1.8V
= 50mA
LOAD
LOAD
LOAD
3406afa
5
LTC3406A
PIN FUNCTIONS
RUN(Pin1):RunControlInput. Forcingthispinabove1.5V
enables the part. Forcing this pin below 0.3V shuts down
thedevice.Inshutdown,allfunctionsaredisableddrawing
<1μA supply current. Do not leave RUN floating.
V (Pin4):MainSupplyPin.Mustbecloselydecoupledto
IN
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.
GND (Pin 2): Ground Pin.
SW (Pin 3): Switch Node Connection to Inductor. This pin
connectstothedrainsoftheinternalmainandsynchronous
power MOSFET switches.
FUNCTIONAL DIAGRAM
SLOPE
COMP
0.65V
OSC
OSC
V
4
IN
FREQ
–
+
SHIFT
V
FB
–
5
SLEEP
+
–
5Ω
0.6V
+
–
+
0.4V
I
COMP
EA
BURST
Q
Q
S
R
SWITCHING
LOGIC
RS LATCH
V
IN
ANTI-
SHOOT-
THRU
AND
BLANKING
CIRCUIT
SW
3
RUN
1
0.6V REF
+
–
SHUTDOWN
I
RCMP
2
GND
3406A BD
3406afa
6
LTC3406A
OPERATION (Refer to Functional Diagram)
Main Control Loop
off, reducing the quiescent current to 20μA. In this sleep
state, the load current is being supplied solely from the
output capacitor. As the output voltage droops, the EA
amplifier’soutputrisesabovethesleepthresholdsignaling
the BURST comparator to trip and turn the top MOSFET
on. This process repeats at a rate that is dependent on
the load demand.
The LTC3406A 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,
I
, resets the RS latch. The peak inductor current at
COMP
COMP
whichI
Dropout Operation
resetstheRSlatch,iscontrolledbytheoutput
Astheinputsupplyvoltagedecreasestoavalueapproach-
ing the output voltage, the duty cycle increases toward the
maximumon-time.Furtherreductionofthesupplyvoltage
forcesthemainswitchtoremainonformorethanonecycle
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.
of error amplifier 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 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
bythecurrentreversalcomparatorI
of the next clock cycle.
, orthebeginning
RCMP
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 LTC3406A is used at 100% duty cycle with low input
voltage (See Thermal Considerations in the Applications
Information section).
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
Burst Mode Operation
Slope compensation provides stability in constant fre-
quency architectures by preventing subharmonic oscilla-
tions at high duty cycles. It is accomplished internally by
addingacompensatingramptotheinductorcurrentsignal
at duty cycles in excess of 40%. Normally, this results in
a reduction of maximum inductor peak current for duty
cycles >40%. However, the LTC3406A uses a patented
scheme that counteracts this compensating ramp, which
allows the maximum inductor peak current to remain
unaffected throughout all duty cycles.
TheLTC3406AiscapableofBurstModeoperationinwhich
the internal power MOSFETs operate intermittently based
on load demand.
In Burst Mode operation, the peak current of the inductor
is set to approximately 100mA regardless of the output
load. Each burst event can last from a few cycles at light
loads to almost continuously cycling with short sleep
intervalsatmoderateloads.Inbetweentheseburstevents,
thepowerMOSFETsandanyunneededcircuitryareturned
3406afa
7
LTC3406A
APPLICATIONS INFORMATION
The basic LTC3406A 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-
Table 1. Representative Surface Mount Inductors
PART
NUMBER
VALUE
(μH)
DCR
MAX DC
SIZE
3
(Ω MAX) CURRENT (A)
W × L × H (mm )
lowed 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
rentasshowninEquation1. Areasonablestartingpointfor
setting ripple current is ∆I = 240mA (40% of 600mA).
L
ꢂ
ꢄ
ꢃ
OUT ꢅ
VIN
ꢆ
V
style inductor to use often depends more on the price vs
sizerequirementsandanyradiatedfield/EMIrequirements
than on what the LTC3406A requires to operate. Table 1
shows some typical surface mount inductors that work
well in LTC3406A applications.
1
ꢀIL =
VOUT 1ꢁ
ꢇ
f L
( )( )
(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 efficiency, choose a low
DC-resistance inductor.
C and C
Selection
IN
OUT
Incontinuousmode,thesourcecurrentofthetopMOSFET
is a square wave of duty cycle V /V . To prevent large
OUT IN
voltage transients, a low ESR input capacitor sized for the
maximumRMScurrentmustbeused.ThemaximumRMS
capacitor current is given by:
The inductor value also has an effect on Burst Mode opera-
tion. The transition to low current operation begins when
the inductor current peaks fall to approximately 100mA.
ꢄ1/2
Lower inductor values (higher ∆I ) will cause this to occur
L
ꢂ
VOUT V ꢁ V
(
)
IN
OUT
ꢃ
ꢅ
CIN required IRMS ꢀIOMAX
at lower load currents, which can cause a dip in efficiency
in the upper range of low current operation. In Burst Mode
operation, lower inductance values will cause the burst
frequency to increase.
VIN
This formula has a maximum at V = 2V , where
IN
OUT
I
= I /2. This simple worst-case condition is
RMS
OUT
commonly used for design because even significant de-
viations do not offer much relief. Note that the capacitor
manufacturer’s ripple current ratings are often based on
2000hoursoflife.Thismakesitadvisabletofurtherderate
the capacitor, or choose a capacitor rated at a higher tem-
perature than required. Always consult the manufacturer
if there is any question.
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
3406afa
8
LTC3406A
APPLICATIONS INFORMATION
induce ringing at the input, V . At best, this ringing can
The selection of C
is driven by the required effective
IN
OUT
couple to the output and be mistaken as loop instability. At
series resistance (ESR).
worst, a sudden inrush of current through the long wires
Typically, once the ESR requirement for C
has been
OUT
can potentially cause a voltage spike at V , large enough
IN
met, the RMS current rating generally far exceeds the
to damage the part.
I
requirement. The output ripple
∆
V
is
RIPPLE(P-P)
determined by:
OUT
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.
ꢂ
ꢅ
ꢇ
1
ꢀVOUT ꢁ ꢀIL ESR+
ꢄ
8fC
ꢃ
OUT ꢆ
where f = operating frequency, C
= output capacitance
OUT
Output Voltage Programming
and
voltage, the output ripple is highest at maximum input
voltage since I increases with input voltage.
∆I = ripple current in the inductor. For a fixed output
L
In the adjustable version, the output voltage is set by a
resistive divider according to the following formula:
∆
L
R2
R1
ꢀ
ꢁ
ꢃ
ꢄ
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.
VOUT = 0.6V 1+
ꢂ
ꢅ
(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
V
FB
LTC3406A
R1
GND
3406A F01
Using Ceramic Input and Output Capacitors
Figure 1. Setting the LTC3406A Output Voltage
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
LTC3406A’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.
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:
Efficiency = 100% – (L1 + L2 + L3 + ...)
However, care must be taken when ceramic capacitors are
usedattheinputandtheoutput.Whenaceramiccapacitor
is used at the input and the power is supplied by a wall
adapter through long wires, a load step at the output can
where L1, L2, etc. are the individual losses as a percent-
age of input power.
3406afa
9
LTC3406A
APPLICATIONS INFORMATION
2
Although all dissipative elements in the circuit produce
losses, two main sources usually account for most of
2. I R losses are calculated from the resistances of the
internal switches, R , and external inductor R . In
SW
L
the losses in LTC3406A circuits: V quiescent current
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
and I R losses. The V quiescent current loss dominates
IN
the efficiency loss at very low load currents whereas the
2
I R 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
DS(ON)TOP
)(1 – DC)
DS(ON)BOT
TheR
forboththetopandbottomMOSFETscanbe
DS(ON)
1
V
IN
= 3.6V
obtained from the Typical Performance Characteristics
2
curves. Thus, to obtain I R losses, simply add R to
SW
0.1
R and multiply the result by the square of the average
L
output current.
0.01
OtherlossesincludingC andC ESRdissipativelosses
IN
OUT
and inductor core losses generally account for less than
0.001
2% total additional loss.
V
V
V
= 1.2V
= 1.8V
= 2.5V
OUT
OUT
OUT
Thermal Considerations
0.0001
0.1
1
10
100
1000
In most applications the LTC3406A does not dissipate
much heat due to its high efficiency. But, in applications
where the LTC3406A 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)
3406A F02
Figure 2. Power Lost 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
ToavoidtheLTC3406Afromexceedingthemaximumjunc-
tion 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:
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
D
JA
their effects will be more pronounced at higher supply
is the thermal resistance from the junction of the die to
voltages.
the ambient temperature.
3406afa
10
LTC3406A
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
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 LTC3406A in dropout at an
input voltage of 2.7V, a load current of 600mA and an
ambient temperature of 70°C. From the typical perfor-
mance 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 0.27Ω. 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
LTC3406A. These items are also illustrated graphically 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
Notethatathighersupplyvoltages,thejunctiontemperature
trace, the V
trace and the V trace should be kept
OUT
IN
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
IN
a load step occurs, V
immediately shifts by an amount
capacitor provides the AC current to the internal power
OUT
equal to (
∆
I
• ESR), where ESR is the effective series
MOSFETs.
LOAD
resistance of C
.
∆
I
also begins to charge or dis-
OUT
LOAD
4. Keep the switching node, SW, away from the sensitive
charge C , which generates a feedback error signal. The
OUT
V
node.
FB
regulator loop then acts to return V
value. During this recovery time V
to its steady-state
can be monitored
OUT
OUT
5. Keep the (–) plates of C and C , and the IC ground,
IN
OUT
as 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.
3406afa
11
LTC3406A
APPLICATIONS INFORMATION
1
2
3
5
4
RUN
V
FB
LTC3406A
GND
R2
R1
–
C
V
OUT
OUT
C
FWD
SW
V
IN
+
L1
C
IN
V
IN
3406A F03
BOLD LINES INDICATE HIGH CURRENT PATHS
Figure 3. LTC3406A Layout Diagram
V
IN
VIA TO V
R1
IN
VIA TO V
OUT
R2
PIN 1
C
FWD
LTC3406A
V
OUT
SW
L1
C
OUT
C
IN
GND
3406A F04
Figure 4. LTC3406A Suggested Layout
Design Example
Substituting V
= 2.5V, V = 4.2V, ∆I = 240mA and
OUT IN L
f = 1.5MHz in Equation (3) gives:
As a design example, assume the LTC3406A 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
1.5MHz(240mA)
2.5V
4.2V
ꢁ
ꢂ
ꢄ
ꢅ
L =
1ꢀ
= 2.81μH
ꢃ
ꢆ
IN
A 2.2μH inductor works well for this application. For best
efficiency choose a 720mA or greater inductor with less
than 0.2Ω 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
ꢂ
ꢄ
ꢃ
OUT ꢅ
VIN
ꢆ
V
1
of less than 0.25Ω. In most cases, a ceramic capacitor
will satisfy this requirement.
L =
VOUT 1ꢁ
ꢇ
f ꢀI
( )
(
)
L
(3)
3406afa
12
LTC3406A
APPLICATIONS INFORMATION
For the feedback resistors, choose R1 = 316k. R2 can
then be calculated from Equation (2) to be:
Figure 5 shows the complete circuit along with its ef-
ficiency curve.
V
0.6
ꢁ
ꢄ
OUT
R2=
ꢀ1 R1=1000k
(4)
ꢃ
ꢆ
ꢂ
ꢅ
2.2μH*
V
OUT
4
1
3
5
V
IN
2.5V
V
SW
LTC3406A
RUN
IN
2.7V TO 4.2V
†
22pF
C
600mA
IN
C
10μF
CER
**
4.7μF
CER
OUT
V
FB
1M
GND
2
316k
3406A F05a
*MURATA LQH32CN2R2M33
**TAIYO YUDEN JMK316BJ106ML
† TAIYO YUDEN LMK212BJ475MG
100
90
80
70
60
50
40
30
20
10
0
V
OUT
100mV/DIV
I
L
500mA/DIV
I
LOAD
500mA/DIV
V
V
V
= 2.7V
= 3.6V
= 4.2V
IN
IN
IN
3406A F05d
V
V
LOAD
= 3.6V
20μs/DIV
IN
= 2.5V
OUT
I
= 300mA TO 600mA
0.1
1
10
100
1000
OUTPUT CURRENT (mA)
3406A F05b
Figure 5.
3406afa
13
LTC3406A
TYPICAL APPLICATIONS
Single Li-Ion 1.2V/600mA Regulator for High Efficiency and Small Footprint
2.2μH*
22pF
V
OUT
4
3
V
IN
1.2V
V
SW
LTC3406A
RUN
IN
†
600mA
**
C
IN
C
10μF
CER
4.7μF
CER
OUT
1
5
V
FB
301k
301k
GND
2
*MURATA LQH32CN2R2M33
**TAIYO YUDEN JMK316BJ106ML
† TAIYO YUDEN JMK212BJ475MG
3406A TA02
Efficiency vs Load Current
Load Step
100
90
80
70
60
50
40
30
20
10
0
V
OUT
100mV/DIV
I
L
500mA/DIV
I
LOAD
500mA/DIV
V
V
V
= 2.7V
= 3.6V
= 4.2V
IN
IN
IN
3406A TA05
V
V
= 3.6V
20μs/DIV
IN
V
= 1.2V
1
= 1.2V
OUT
OUT
I
= 300mA TO 600mA
LOAD
0.1
10
100
1000
OUTPUT CURRENT (mA)
3406A TA03
3406afa
14
LTC3406A
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 REV B
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
3406afa
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.
15
LTC3406A
RELATED PARTS
PART NUMBER
DESCRIPTION
COMMENTS
96% Efficiency, V : 2.5V to 5.5V, V
LTC3406/LTC3406B
600mA (I ), 1.5MHz, Synchronous
= 0.6V, I = 20μA,
Q
OUT
IN
OUT(MIN)
OUT(MIN)
OUT(MIN)
OUT(MIN)
OUT(MIN)
OUT(MIN)
OUT(MIN)
OUT(MIN)
OUT(MIN)
OUT(MIN)
OUT(MIN)
OUT(MIN)
OUT(MIN)
OUT(MIN)
OUT(MIN)
Step-Down 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,
Q
OUT
IN
Synchronous Step-Down DC/DC Converters
I
<1μA, MS10E, DFN Packages
300mA (I ), 2.25MHz, Synchronous
95% Efficiency, V : 2.5V to 5.5V, V
= 0.8V, I = 26μA,
Q
OUT
IN
Step-Down DC/DC Converters
I
SD
<1μA, SC70 Package
1.25A (I ), 4MHz, Synchronous
95% Efficiency, V : 2.5V to 5.5V, V
= 0.8V, I = 60μA,
Q
OUT
IN
Step-Down DC/DC Converter
I
SD
<1μA, MS10, DFN Packages
LTC3412
2.5A (I ), 4MHz, Synchronous
95% Efficiency, V : 2.5V to 5.5V, V
= 0.8V, I = 60μA,
Q
OUT
IN
Step-Down DC/DC Converter
I
SD
<1μA, TSSOP-16E Package
LTC3440
600mA (I ), 2MHz, Synchronous
95% Efficiency, V : 2.5V to 5.5V, V
: 2.5V to 5.5V, I = 25μA,
Q
OUT
IN
Buck-Boost DC/DC Converter
I
SD
<1μA, MS10, DFN Packages
LTC3530
600mA (I ), 2MHz, Synchronous
95% Efficiency, V : 1.8V to 5.5V, V
: 1.8V to 5.25V, I = 40μA,
Q
OUT
IN
Buck-Boost DC/DC Converter
I
SD
<1μA, MS10, DFN Packages
LTC3531/LTC3531-3/
LTC3531-3.3
200mA (I ), 1.5MHz, Synchronous
95% Efficiency, V : 1.8V to 5.5V, V
: 2V to 5V, I = 16μA,
Q
OUT
IN
Buck-Boost DC/DC Converters
I
SD
<1μA, ThinSOT, DFN Packages
LTC3532
500mA (I ), 2MHz, Synchronous
95% Efficiency, V : 2.4V to 5.5V, V
: 2.4V to 5.25V, I = 35μA,
Q
OUT
IN
Buck-Boost DC/DC Converter
I
SD
<1μA, MS10, DFN Packages
LTC3542
500mA (I ), 2.25MHz, Synchronous
95% Efficiency, V : 2.5V to 5.5V, V
= 0.6V, I = 26μA,
Q
OUT
IN
Step-Down DC/DC Converter
I
SD
<1μA, 2mm × 2mm DFN Package
LTC3544/LTC3544B
LTC3547/LTC3547B
Quad 300mA + 2
×
200mA + 100mA, 2.25MHz, 95% Efficiency, V : 2.5V to 5.5V, V
= 0.8V, I = 70μA,
Q
IN
Synchronous Step-Down DC/DC Converters
I
SD
<1μA, 3mm × 3mm QFN Package
Dual 300mA, 2.25MHz, Synchronous
Step-Down DC/DC Converters
96% Efficiency, V : 2.5V to 5.5V, V
= 0.6V, I = 40μA,
Q
IN
I
SD
<1μA, 2mm × 3mm DFN Package
LTC3548/LTC3548-1/
LTC3548-2
Dual 400mA/800mA (I ), 2.25MHz,
95% Efficiency, V : 2.5V to 5.5V, V
= 0.6V, I = 40μA,
Q
OUT
IN
Synchronous Step-Down DC/DC Converters
I
SD
<1μA, MS10E, DFN Packages
LTC3560
800mA (I ), 2.25MHz, Synchronous
95% Efficiency, V : 2.5V to 5.5V, V
= 0.6V, I = 16μA,
Q
OUT
IN
Step-Down DC/DC Converter
I
SD
<1μA, ThinSOT Package
LTC3561
1.25A (I ), 4MHz, Synchronous
95% Efficiency, V : 2.5V to 5.5V, V
= 0.8V, I = 240μA,
Q
OUT
IN
Step-Down DC/DC Converter
I
SD
<1μA, DFN Package
3406afa
LT 1207 REV A • PRINTED IN USA
LinearTechnology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
16
●
●
© LINEAR TECHNOLOGY CORPORATION 2007
(408) 432-1900 FAX: (408) 434-0507 www.linear.com
相关型号：
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LTC3406B-2 - 2.25MHz, 600mA Synchronous Step-Down Regulator in ThinSOT; Package: SOT; Pins: 5; Temperature Range: -40°C to 85°C
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