LTC3406B-1.5 [Linear]
1.5MHz, 600mA Synchronous Step-Down egulator in ThinSOT; 为1.5MHz ， 600mA同步降压型egulator采用ThinSOT
| 型号： | LTC3406B-1.5 |
| 厂家： | 
Linear |
| 描述： | 1.5MHz, 600mA Synchronous Step-Down egulator in ThinSOT |
| 文件： | 总16页 (文件大小：229K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
LTC3406
LTC3406-1.5/LTC3406-1.8
1.5MHz, 600mA
Synchronous Step-Down
Regulator in ThinSOT
U
FEATURES
DESCRIPTIO
The LTC®3406 is a high efficiency monolithic synchro-
nous buck regulator using a constant frequency, current
mode architecture. The device is available in an adjustable
versionandfixedoutputvoltagesof1.5Vand1.8V. Supply
current during operation is only 20µA and drops to ≤1µA
in shutdown. The 2.5V to 5.5V input voltage range makes
the LTC3406 ideally suited for single Li-Ion battery-pow-
ered applications. 100% duty cycle provides low dropout
operation, extending battery life in portable systems.
Automatic Burst Mode® operation increases efficiency at
light loads, further extending battery life.
■
High Efficiency: Up to 96%
■
Very Low Quiescent Current: Only 20µA
During 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
0.6V Reference Allows Low Output Voltages
Shutdown Mode Draws ≤1µA Supply Current
Current Mode Operation for Excellent Line and
Load Transient Response
Switching frequency is internally set at 1.5MHz, allowing
the use of small surface mount inductors and capacitors.
■
■
Overtemperature Protected
Low Profile (1mm) ThinSOTTM Package
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 feed-
back reference voltage. The LTC3406 is available in a low
profile (1mm) ThinSOT package.
U
APPLICATIO S
■
Cellular Telephones
■
Personal Information Appliances
■
Wireless and DSL Modems
, LTC and LT are registered trademarks of Linear Technology Corporation.
Burst Mode is a registered trademark of Linear Technology Corporation.
ThinSOT is a trademark of Linear Technology Corporation.
■
Digital Still Cameras
Protected by U.S. Patents, including 6580258, 5481178.
■
MP3 Players
■
Portable Instruments
U
TYPICAL APPLICATIO
95
V
= 2.7V
IN
90
85
80
75
70
65
60
2.2µH*
V
V
IN
OUT
4
1
3
5
V
= 3.6V
IN
2.7V
1.8V
V
SW
IN
†
C
C
**
TO 5.5V
OUT
600mA
IN
10µF
V
= 4.2V
4.7µF
IN
LTC3406-1.8
CER
CER
3406 F01a
RUN
V
OUT
GND
2
V
= 1.8V
OUT
*MURATA LQH32CN2R2M33
0.1
1
10
100
1000
**TAIYO YUDEN JMK212BJ475MG
†TAIYO YUDEN JMK316BJ106ML
OUTPUT CURRENT (mA)
3406 F01b
Figure 1a. High Efficiency Step-Down Converter
Figure 1b. Efficiency vs Load Current
3406fa
1
LTC3406
LTC3406-1.5/LTC3406-1.8
W W U W
ABSOLUTE AXI U RATI GS (Note 1)
Peak SW Sink and Source Current ........................ 1.3A
Operating Temperature Range (Note 2) .. –40°C to 85°C
Junction Temperature (Note 3)............................ 125°C
Storage Temperature Range ................ –65°C to 150°C
Lead Temperature (Soldering, 10 sec)................. 300°C
Input Supply Voltage .................................. –0.3V to 6V
RUN, VFB Voltages ..................................... –0.3V to VIN
SW Voltage .................................. –0.3V to (VIN + 0.3V)
P-Channel Switch Source Current (DC) ............. 800mA
N-Channel Switch Sink Current (DC) ................. 800mA
U W
U
PACKAGE/ORDER I FOR ATIO
ORDER PART
NUMBER
ORDER PART
NUMBER
TOP VIEW
TOP VIEW
RUN 1
GND 2
SW 3
5 V
4 V
RUN 1
GND 2
SW 3
5 V
4 V
FB
OUT
IN
LTC3406ES5-1.5
LTC3406ES5-1.8
LTC3406ES5
IN
S5 PART MARKING
LTA5
S5 PART MARKING
S5 PACKAGE
S5 PACKAGE
5-LEAD PLASTIC TSOT-23
5-LEAD PLASTIC TSOT-23
TJMAX = 125°C, θJA = 250°C/ W, θJC = 90°C/ W
TJMAX = 125°C, θJA = 250°C/ W, θJC = 90°C/ W
LTD6
LTC4
Consult LTC Marketing for parts specified with wider operating temperature ranges.
ELECTRICAL CHARACTERISTICS
The ● denotes specifications which apply over the full operating temperature range, otherwise specifications are 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
LTC3406 (Note 4) T = 25°C
0.5880
0.5865
0.5850
0.6
0.6
0.6
0.6120
0.6135
0.6150
V
V
V
FB
A
LTC3406 (Note 4) 0°C T ≤ 85°C
A
LTC3406 (Note 4) –40°C ≤ T ≤ 85°C
●
●
A
∆V
Reference Voltage Line Regulation
Regulated Output Voltage
V
= 2.5V to 5.5V (Note 4)
IN
0.04
0.4
%/V
FB
V
LTC3406-1.5, I
LTC3406-1.8, I
= 100mA
= 100mA
●
●
1.455
1.746
1.500
1.800
1.545
1.854
V
V
OUT
OUT
OUT
∆V
Output Voltage Line Regulation
Peak Inductor Current
V
V
= 2.5V to 5.5V
●
0.04
1
0.4
%/V
A
OUT
IN
I
= 3V, V = 0.5V or V = 90%,
OUT
0.75
2.5
1.25
PK
IN
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
(Note 5)
S
V
V
V
= 0.5V or V
= 0.62V or V
= 90%, I = 0A
LOAD
300
20
0.1
400
35
1
µA
µA
µA
FB
OUT
= 103%, I
= 0A
FB
OUT
LOAD
Shutdown
= 0V, V = 4.2V
RUN
IN
f
Oscillator Frequency
V
V
= 0.6V or V = 100%
OUT
●
1.2
1.5
210
1.8
MHz
kHz
OSC
FB
FB
= 0V or V
= 0V
OUT
R
R
R
R
of P-Channel FET
of N-Channel FET
I
I
= 100mA
0.4
0.35
0.5
0.45
±1
Ω
Ω
PFET
NFET
LSW
DS(ON)
SW
SW
= –100mA
= 0V, V = 0V or 5V, V = 5V
DS(ON)
I
SW Leakage
V
±0.01
µA
RUN
SW
IN
3406fa
2
LTC3406
LTC3406-1.5/LTC3406-1.8
ELECTRICAL CHARACTERISTICS
The ● denotes specifications which apply over the full operating temperature range, otherwise specifications are TA = 25°C.
VIN = 3.6V unless otherwise specified.
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
1
MAX
1.5
UNITS
V
V
RUN Threshold
RUN Leakage Current
●
●
0.3
RUN
RUN
I
±0.01
±1
µA
Note 1: Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
Note 3: T is calculated from the ambient temperature T and power
J A
dissipation P according to the following formula:
D
Note 2: The LTC3406E is guaranteed to meet performance specifications
from 0°C to 70°C. Specifications over the –40°C to 85°C operating
temperature range are assured by design, characterization and correlation
with statistical process controls.
LTC3406: T = T + (P )(250°C/W)
J A D
Note 4: The LTC3406 is tested in a proprietary test mode that connects
to the output of the error amplifier.
V
FB
Note 5: Dynamic supply current is higher due to the gate charge being
delivered at the switching frequency.
U W
TYPICAL PERFOR A CE CHARACTERISTICS
(From Figure1a Except for the Resistive Divider Resistor Values)
Efficiency vs Input Voltage
Efficiency vs Output Current
Efficiency vs Output Current
100
95
90
85
80
75
70
65
60
55
50
95
90
85
80
75
70
65
60
95
90
85
80
75
70
65
60
V
OUT
= 1.2V
V
= 1.5V
OUT
I
= 100mA
OUT
I
= 10mA
OUT
V
IN
= 2.7V
V
= 2.7V
IN
I
= 1mA
OUT
V
= 4.2V
IN
V
IN
= 4.2V
I
= 600mA
OUT
V
IN
= 3.6V
V
= 3.6V
IN
I
= 0.1mA
OUT
V
= 1.8V
3
OUT
2
4
INPUT VOLTAGE (V)
5
6
0.1
1
10
100
1000
0.1
1
10
100
1000
OUTPUT CURRENT (mA)
OUTPUT CURRENT (mA)
3406 G02
3406 G03
3406 G01
Reference Voltage vs
Temperature
Oscillator Frequency vs
Temperature
Efficiency vs Output Current
0.614
0.609
0.604
0.599
0.594
0.589
0.584
1.70
1.65
1.60
1.55
1.50
1.45
1.40
1.35
1.30
100
95
90
85
80
75
70
65
60
V
= 2.5V
OUT
V
= 3.6V
IN
V
= 3.6V
IN
V
= 2.7V
IN
V
= 3.6V
IN
V
= 4.2V
IN
50
TEMPERATURE (°C)
100 125
50
TEMPERATURE (°C)
100 125
–50 –25
0
25
75
–50
25
75
–25
0
0.1
1
10
100
1000
OUTPUT CURRENT (mA)
3406 G04
3406 G05
3406 G06
3406fa
3
LTC3406
LTC3406-1.5/LTC3406-1.8
U W
TYPICAL PERFOR A CE CHARACTERISTICS
(From Figure1a Except for the Resistive Divider Resistor Values)
Oscillator Frequency vs
Supply Voltage
R
DS(ON) vs Input Voltage
Output Voltage vs Load Current
1.844
1.834
1.824
1.814
1.804
1.794
1.784
1.774
1.8
1.7
1.6
1.5
1.4
1.3
1.2
0.7
0.6
V
= 3.6V
IN
0.5
0.4
0.3
0.2
0.1
MAIN
SWITCH
SYNCHRONOUS
SWITCH
0
0
100
900
2
3
4
5
6
200 300 400 500 600 700 800
LOAD CURRENT (mA)
5
7
0
1
2
3
4
6
SUPPLY VOLTAGE (V)
INPUT VOLTAGE (V)
3406 G07
3406 G08
3406 G09
RDS(ON) vs Temperature
Supply Current vs Supply Voltage
Supply Current vs Temperature
50
45
40
35
30
25
20
15
10
5
50
45
40
35
30
25
20
15
10
5
0.7
0.6
V
V
LOAD
= 3.6V
V
I
= 1.8V
= 0A
IN
OUT
LOAD
V
IN
= 2.7V
= 1.8V
= 0A
OUT
I
V
IN
= 3.6V
V
IN
= 4.2V
0.5
0.4
0.3
0.2
0.1
MAIN SWITCH
SYNCHRONOUS SWITCH
0
0
0
–50
0
25
50
75 100 125
2
3
4
5
6
–25
50
TEMPERATURE (°C)
100 125
–50 –25
0
25
75
TEMPERATURE (°C)
SUPPLY VOLTAGE (V)
3406 G12
3406 G11
3406 G10
Switch Leakage vs Temperature
Switch Leakage vs Input Voltage
Burst Mode Operation
120
100
80
60
40
20
0
300
250
200
150
RUN = 0V
V
= 5.5V
IN
RUN = 0V
SW
5V/DIV
SYNCHRONOUS
SWITCH
V
OUT
100mV/DIV
AC COUPLED
MAIN
SWITCH
I
L
200mA/DIV
100
50
0
MAIN SWITCH
SYNCHRONOUS SWITCH
3406 G15
V
V
= 3.6V
4µs/DIV
IN
= 1.8V
OUT
I
= 50mA
LOAD
0
2
3
4
5
6
50
TEMPERATURE (°C)
100 125
1
–50 –25
0
25
75
INPUT VOLTAGE (V)
3406 G14
3406 G13
3406fa
4
LTC3406
LTC3406-1.5/LTC3406-1.8
U W
TYPICAL PERFOR A CE CHARACTERISTICS
(From Figure 1a Except for the Resistive Divider Resistor Values)
Start-Up from Shutdown
Load Step
Load Step
V
OUT
100mV/DIV
RUN
V
OUT
AC COUPLED
2V/DIV
100mV/DIV
AC COUPLED
V
OUT
2V/DIV
I
L
I
L
500mA/DIV
500mA/DIV
I
LOAD
500mA/DIV
I
I
LOAD
LOAD
500mA/DIV
500mA/DIV
3406 G18
3406 G17
3406 G16
V
V
I
= 3.6V
20µs/DIV
V
V
I
= 3.6V
20µs/DIV
V
V
I
= 3.6V
40µs/DIV
IN
OUT
IN
OUT
IN
OUT
= 1.8V
= 1.8V
= 0mA TO 600mA
= 1.8V
= 50mA TO 600mA
= 600mA
LOAD
LOAD
LOAD
Load Step
Load Step
V
V
OUT
OUT
100mV/DIV
100mV/DIV
AC COUPLED
AC COUPLED
I
I
L
L
500mA/DIV
500mA/DIV
I
I
LOAD
LOAD
500mA/DIV
500mA/DIV
3406 G19
3406 G20
V
V
I
= 3.6V
20µs/DIV
V
V
I
= 3.6V
20µs/DIV
IN
OUT
IN
OUT
= 1.8V
= 1.8V
= 100mA TO 600mA
= 200mA TO 600mA
LOAD
LOAD
U
U
U
PI FU CTIO S
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.
VIN (Pin 4): Main Supply Pin. Must be closely decoupled
to GND, Pin 2, with a 2.2µF or greater ceramic capacitor.
VFB (Pin 5) (LTC3406): Feedback Pin. Receives the feed-
back voltage from an external resistive divider across the
output.
GND (Pin 2): Ground Pin.
SW (Pin 3): Switch Node Connection to Inductor. This pin
connects to the drains of the internal main and synchro-
nous power MOSFET switches.
VOUT (Pin 5) (LTC3406-1.5/LTC3406-1.8): Output Volt-
age Feedback Pin. An internal resistive divider divides the
output voltage down for comparison to the internal refer-
ence voltage.
3406fa
5
LTC3406
LTC3406-1.5/LTC3406-1.8
U
U
W
FU CTIO AL DIAGRA
SLOPE
COMP
0.65V
OSC
OSC
V
IN
4
FREQ
–
+
SHIFT
V
/V
FB OUT
–
+
5
SLEEP
+
–
5Ω
0.6V
+
–
LTC3406-1.5
R1
R2
0.4V
I
COMP
EA
FB
R1 + R2 = 550k
BURST
LTC3406-1.8
R1 + R2 = 540k
Q
Q
S
R
SWITCHING
LOGIC
AND
RS LATCH
V
ANTI-
SHOOT-
THRU
IN
BLANKING
CIRCUIT
SW
3
RUN
1
0.6V REF
+
–
SHUTDOWN
I
RCMP
2
GND
3406 BD
U
OPERATIO
(Refer to Functional Diagram)
Burst Mode Operation
Main Control Loop
The LTC3406 is capable of Burst Mode operation in which
the internal power MOSFETs operate intermittently based
on load demand.
The LTC3406 uses a constant frequency, current mode
step-down architecture. Both the main (P-channel
MOSFET)andsynchronous(N-channelMOSFET)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 com-
parator, ICOMP, resets the RS latch. The peak inductor
current at which ICOMP resets the RS latch, is controlled by
the output 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 cur-
rent. While the top MOSFET is off, the bottom MOSFET is
turnedonuntileithertheinductorcurrentstartstoreverse,
as indicated by the current reversal comparator IRCMP, or
the beginning of the next clock cycle.
In Burst Mode operation, the peak current of the inductor
is set to approximately 200mA 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
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’s output rises above the sleep threshold signal-
ingtheBURSTcomparatortotripandturnthetopMOSFET
on. This process repeats at a rate that is dependent on the
load demand.
3406fa
6
LTC3406
LTC3406-1.5/LTC3406-1.8
U
OPERATIO
(Refer to Functional Diagram)
Short-Circuit Protection
in the maximum output current as a function of input
voltage for various output voltages.
Whentheoutputisshortedtoground, thefrequencyofthe
oscillator is reduced to about 210kHz, 1/7 the nominal
frequency. This frequency foldback ensures that the in-
ductorcurrenthasmoretimetodecay, therebypreventing
runaway. The oscillator’s frequency will progressively
increase to 1.5MHz when VFB or VOUT rises above 0V.
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 LTC3406 uses a
patent-pending scheme that counteracts this compensat-
ing ramp, which allows the maximum inductor peak
current to remain unaffected throughout all duty cycles.
Dropout Operation
Astheinputsupplyvoltagedecreasestoavalueapproach-
ing the output voltage, the duty cycle increases toward the
maximumon-time.Furtherreductionofthesupplyvoltage
forcesthemainswitchtoremainonformorethanonecycle
untilitreaches100%dutycycle.Theoutputvoltagewillthen
be determined by the input voltage minus the voltage drop
across the P-channel MOSFET and the inductor.
1200
1000
Animportantdetailtorememberisthatatlowinputsupply
voltages, the RDS(ON) of the P-channel switch increases
(see Typical Performance Characteristics). Therefore, the
user should calculate the power dissipation when the
LTC3406isusedat100%dutycyclewithlowinputvoltage
(See Thermal Considerations in the Applications Informa-
tion section).
V
V
= 1.8V
= 1.5V
OUT
OUT
800
600
400
200
0
V
= 2.5V
OUT
Low Supply Operation
2.5
3.5
4.0
4.5
5.0
5.5
3.0
SUPPLY VOLTAGE (V)
The LTC3406 will operate with input supply voltages as
low as 2.5V, but the maximum allowable output current is
reduced at this low voltage. Figure 2 shows the reduction
3406 F02
Figure 2. Maximum Output Current vs Input Voltage
3406fa
7
LTC3406
LTC3406-1.5/LTC3406-1.8
W U U
U
APPLICATIO S I FOR ATIO
The basic LTC3406 application circuit is shown in Figure 1.
Externalcomponentselectionisdrivenbytheloadrequire-
ment and begins with the selection of L followed by CIN and
inductor to use often depends more on the price vs size
requirements and any radiated field/EMI requirements
than on what the LTC3406 requires to operate. Table 1
shows some typical surface mount inductors that work
well in LTC3406 applications.
COUT
.
Inductor Selection
Table 1. Representative Surface Mount Inductors
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 VIN or VOUT also increases the ripple
currentasshowninequation1. Areasonablestartingpoint
for setting ripple current is ∆IL = 240mA (40% of 600mA).
PART
NUMBER
VALUE
(µH)
DCR
MAX DC
SIZE
3
(Ω MAX) CURRENT (A) W × L × H (mm )
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
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
⎛
VOUT
V
IN
⎞
1
∆IL =
VOUT 1−
⎜
⎟
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
(1)
f L
( )( )
⎝
⎠
Murata
LQH32CN
1.0
2.2
4.7
0.060
0.097
0.150
1.00
0.79
0.65
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
inductorshouldbeenoughformostapplications(600mA
+ 120mA). For better efficiency, choose a low DC-resis-
tance inductor.
CIN and COUT Selection
Incontinuousmode,thesourcecurrentofthetopMOSFET
is a square wave of duty cycle VOUT/VIN. 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:
The inductor value also has an effect on Burst Mode
operation. The transition to low current operation begins
when the inductor current peaks fall to approximately
200mA. Lower inductor values (higher ∆IL) will cause this
to occur 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.
1/2
]
V
V − V
OUT
(
)
[
OUT IN
CIN required IRMS ≅ IOMAX
V
IN
This formula has a maximum at VIN = 2VOUT, where
RMS = IOUT/2. This simple worst-case condition is com-
I
Inductor Core Selection
monlyusedfordesignbecauseevensignificantdeviations
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
temperature than required. Always consult the manufac-
turer if there is any question.
Different core materials and shapes will change the size/
current and price/current relationship of an inductor.
Toroid or shielded pot cores in ferrite or permalloy mate-
rials are small and don’t radiate much energy, but gener-
ally cost more than powdered iron core inductors with
similarelectricalcharacteristics. Thechoiceofwhichstyle
3406fa
8
LTC3406
LTC3406-1.5/LTC3406-1.8
W U U
APPLICATIO S I FOR ATIO
U
The selection of COUT is driven by the required effective
induce ringing at the input, VIN. 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 VIN, large enough
to damage the part.
series resistance (ESR).
Typically, once the ESR requirement for COUT has been
met, the RMS current rating generally far exceeds the
I
RIPPLE(P-P) requirement.Theoutputripple∆VOUT isdeter-
mined by:
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.
⎛
1
⎞
∆VOUT ≅ ∆I ESR +
⎜
⎟
L
⎝
8fCOUT
⎠
where f = operating frequency, COUT = output capacitance
and ∆IL = ripple current in the inductor. For a fixed output
voltage, the output ripple is highest at maximum input
voltage since ∆IL increases with input voltage.
Output Voltage Programming (LTC3406 Only)
In the adjustable version, the output voltage is set by a
resistive divider according to the following formula:
R2
R1
⎛
⎝
⎞
⎟
⎠
Aluminum electrolytic and dry tantalum capacitors are
bothavailableinsurfacemountconfigurations.Inthecase
oftantalum,itiscriticalthatthecapacitorsaresurgetested
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+
⎜
(2)
The external resistive divider is connected to the output,
allowing remote voltage sensing as shown in Figure 3.
0.6V ≤ V
≤ 5.5V
OUT
R2
V
FB
LTC3406
R1
GND
3406 F03
Using 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
LTC3406’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.
Figure 3. Setting the LTC3406 Output Voltage
Efficiency Considerations
The efficiency of a switching regulator is equal to the
output power divided by the input power times 100%. It is
oftenusefultoanalyzeindividuallossestodeterminewhat
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
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
Efficiency = 100% – (L1 + L2 + L3 + ...)
whereL1, L2, etc. aretheindividuallossesasapercentage
of input power.
3406fa
9
LTC3406
LTC3406-1.5/LTC3406-1.8
W U U
U
APPLICATIO S I FOR ATIO
Although all dissipative elements in the circuit produce
losses, two main sources usually account for most of the
losses in LTC3406 circuits: VIN quiescent current and I2R
losses. The VIN quiescent current loss dominates the
efficiency loss at very low load currents whereas the I2R
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 4.
2. I2R losses are calculated from the resistances of the
internal switches, RSW, and external inductor RL. In
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 RDS(ON) and the duty cycle
(DC) as follows:
RSW = (RDS(ON)TOP)(DC) + (RDS(ON)BOT)(1 – DC)
The RDS(ON) for both the top and bottom MOSFETs can
beobtainedfromtheTypicalPerformanceCharateristics
curves. Thus, to obtain I2R losses, simply add RSW to
RL and multiply the result by the square of the average
output current.
1
V
V
V
V
= 1.2V
= 1.5V
= 1.8V
= 2.5V
OUT
OUT
OUT
OUT
0.1
0.01
Other losses including CIN and COUT ESR dissipative
losses and inductor core losses generally account for less
than 2% total additional loss.
0.001
0.0001
0.00001
Thermal Considerations
0.1
1
10
100
1000
In most applications the LTC3406 does not dissipate
much heat due to its high efficiency. But, in applications
where the LTC3406 is running at high ambient tempera-
ture with low supply voltage and high duty cycles, such
as in dropout, the heat dissipated may exceed the maxi-
mum 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.
LOAD CURRENT (mA)
3406 F04
Figure 4. Power Lost vs Load Current
1. The VIN quiescent current is due to two components:
the DC bias current as given in the electrical character-
istics 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 VIN to ground. The resulting
dQ/dtisthecurrentoutofVINthatistypicallylargerthan
To avoid the LTC3406 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 tempera-
ture rise is given by:
the DC bias current. In continuous mode, IGATECHG
=
f(QT + QB) where QT and QB are the gate charges of the
internal top and bottom switches. Both the DC bias and
gate charge losses are proportional to VIN and thus
their effects will be more pronounced at higher supply
voltages.
TR = (PD)(θJA)
where PD is the power dissipated by the regulator and θJA
is the thermal resistance from the junction of the die to the
ambient temperature.
3406fa
10
LTC3406
LTC3406-1.5/LTC3406-1.8
W U U
APPLICATIO S I FOR ATIO
U
The junction temperature, TJ, is given by:
A second, more severe transient is caused by switching in
loads with large (>1µF) supply bypass capacitors. The
dischargedbypasscapacitorsareeffectivelyputinparallel
with COUT, causing a rapid drop in VOUT. 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 • CLOAD).
Thus, a 10µF capacitor charging to 3.3V would require a
250µs rise time, limiting the charging current to about
130mA.
TJ = TA + TR
where TA is the ambient temperature.
As an example, consider the LTC3406 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 RDS(ON) of the
P-channel switch at 70°C is approximately 0.52Ω. There-
fore, power dissipated by the part is:
PD = ILOAD2 • RDS(ON) = 187.2mW
PC Board Layout Checklist
For the SOT-23 package, the θJA is 250°C/W. Thus, the
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
LTC3406. These items are also illustrated graphically in
Figures 5 and 6. Check the following in your layout:
TJ = 70°C + (0.1872)(250) = 116.8°C
which is below the maximum junction temperature of
125°C.
1. The power traces, consisting of the GND trace, the SW
trace and the VIN trace should be kept short, direct and
wide.
Note that at higher supply voltages, the junction tempera-
ture is lower due to reduced switch resistance (RDS(ON)).
Checking Transient Response
2. Does the VFB pin connect directly to the feedback
resistors? The resistive divider R1/R2 must be con-
nected between the (+) plate of COUT and ground.
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, VOUT immediately shifts by an amount
equal to (∆ILOAD • ESR), where ESR is the effective series
resistance of COUT. ∆ILOAD also begins to charge or
discharge COUT, which generates a feedback error signal.
The regulator loop then acts to return VOUT to its steady-
state value. During this recovery time VOUT can be moni-
toredforovershootorringingthatwouldindicateastability
problem. For a detailed explanation of switching control
loop theory, see Application Note 76.
3. Does the (+) plate of CIN connect to VIN as closely as
possible? This capacitor provides the AC current to the
internal power MOSFETs.
4. Keep the switching node, SW, away from the sensitive
VFB node.
5. Keepthe(–)platesofCIN andCOUT ascloseaspossible.
3406fa
11
LTC3406
LTC3406-1.5/LTC3406-1.8
W U U
U
APPLICATIO S I FOR ATIO
1
2
3
5
4
RUN
V
FB
1
2
3
LTC3406
GND
R2
R1
RUN
LTC3406-1.8
–
+
5
4
C
V
OUT
OUT
C
FWD
GND
V
OUT
–
+
SW
V
IN
C
V
OUT
OUT
L1
C
IN
SW
V
IN
L1
V
IN
C
IN
V
IN
3406 F05b
3406 F05a
BOLD LINES INDICATE HIGH CURRENT PATHS
BOLD LINES INDICATE HIGH CURRENT PATHS
Figure 5a. LTC3406 Layout Diagram
Figure 5b. LTC3406-1.8 Layout Diagram
VIA TO GND
R1
VIA TO V
OUT
V
IN
V
IN
VIA TO V
VIA TO V
IN
IN
VIA TO V
OUT
R2
PIN 1
PIN 1
C
FWD
LTC3406-1.8
V
OUT
LTC3406
V
OUT
SW
L1
SW
L1
C
OUT
C
IN
C
OUT
C
IN
GND
GND
3406 F06b
3406 F06a
Figure 6a. LTC3406 Suggested Layout
Figure 6b. LTC3406-1.8 Suggested Layout
Design Example
Substituting VOUT = 2.5V, VIN = 4.2V, ∆IL = 240mA and
f = 1.5MHz in equation (3) gives:
As a design example, assume the LTC3406 is used in a
single lithium-ion battery-powered cellular phone
application. The VIN 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
standbymode, requiringonly2mA. Efficiencyatbothlow
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
⎛
⎜
⎝
⎞
⎟
⎠
L =
1−
= 2.81µH
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.
CIN will require an RMS current rating of at least 0.3A ≅
ILOAD(MAX)/2 at temperature and COUT will require an ESR
of less than 0.25Ω. In most cases, a ceramic capacitor will
satisfy this requirement.
1
⎛
VOUT
V
IN
⎞
L =
VOUT 1−
⎜
⎟
(3)
f ∆I
( )(
⎝
⎠
)
L
3406fa
12
LTC3406
LTC3406-1.5/LTC3406-1.8
W U U
APPLICATIO S I FOR ATIO
U
For the feedback resistors, choose R1 = 316k. R2 can
then be calculated from equation (2) to be:
Figure 7 shows the complete circuit along with its effi-
ciency curve.
V
0.6
⎛
⎜
⎝
⎞
⎠
OUT
100
R2 =
− 1 R1= 1000k
⎟
V
= 2.5V
OUT
95
90
85
80
75
70
65
60
V
= 2.7V
IN
V
= 3.6V
IN
2.2µH*
V
IN
2.7V
TO 4.2V
4
3
5
V
V
= 4.2V
OUT
IN
V
SW
LTC3406
RUN
IN
2.5V
†
22pF
C
IN
C
**
2.2µF
OUT
10µF
CER
CER
1
V
FB
1M
GND
2
316k
3406 F07a
0.1
1
10
100
1000
*MURATA LQH32CN2R2M33
**TAIYO YUDEN JMK316BJ106ML
† TAIYO YUDEN LMK212BJ225MG
OUTPUT CURRENT (mA)
3406 F07b
Figure 7b
Figure 7a
U
TYPICAL APPLICATIO S
Single Li-Ion 1.5V/600mA Regulator for
High Efficiency and Small Footprint
2.2µH*
V
IN
4
3
V
OUT
1.5V
2.7V
V
SW
IN
C
**
TO 4.2V
IN
†
C
LTC3406-1.5
RUN
OUT1
4.7µF
1
10µF
CER
CER
5
V
OUT
GND
3406 TA05
2
*MURATA LQH32CN2R2M33
**TAIYO YUDEN JMK212BJ475MG
†
TAIYO YUDEN JMK316BJ106ML
95
90
85
80
75
70
65
60
V
= 1.5V
= 2.7V
V
OUT
OUT
V
OUT
100mV/DIV
100mV/DIV
AC COUPLED
V
IN
AC COUPLED
V
= 4.2V
IN
I
L
I
L
500mA/DIV
500mA/DIV
V
= 3.6V
IN
I
I
LOAD
LOAD
500mA/DIV
500mA/DIV
3406 TA07
3406 TA08
V
V
I
= 3.6V
20µs/DIV
V
V
I
= 3.6V
20µs/DIV
IN
IN
OUT
= 1.5V
= 1.5V
= 200mA TO 600mA
OUT
= 0A TO 600mA
LOAD
LOAD
0.1
1
10
100
1000
OUTPUT CURRENT (mA)
3406 TA06
3406fa
13
LTC3406
LTC3406-1.5/LTC3406-1.8
U
TYPICAL APPLICATIO S
Single Li-Ion 1.2V/600mA Regulator for High Efficiency and Small Footprint
2.2µH*
V
IN
4
3
V
OUT
1.2V
2.7V
V
SW
LTC3406
RUN
IN
†
22pF
C
TO 4.2V
IN
C
**
2.2µF
CER
OUT
10µF
CER
1
5
V
FB
301k
301k
GND
2
*MURATA LQH32CN2R2M33
**TAIYO YUDEN JMK316BJ106ML
† TAIYO YUDEN LMK212BJ225MG
3406 TA09
95
90
85
80
75
70
65
60
V
= 1.2V
V
OUT
OUT
V
OUT
100mV/DIV
V
= 2.7V
IN
100mV/DIV
AC COUPLED
AC COUPLED
I
L
I
L
V
= 4.2V
IN
500mA/DIV
500mA/DIV
V
= 3.6V
IN
I
I
LOAD
LOAD
500mA/DIV
500mA/DIV
3406 TA11
3406 TA12
V
V
I
= 3.6V
20µs/DIV
V
V
I
= 3.6V
20µs/DIV
IN
OUT
IN
OUT
= 1.2V
= 0mA TO 600mA
= 1.2V
= 200mA TO 600mA
LOAD
LOAD
0.1
1
10
100
1000
OUTPUT CURRENT (mA)
3406 TA10
Tiny 3.3V/600mA Buck Regulator
2.2µH*
V
OUT
3.3V
4
3
V
IN
5V
V
SW
LTC3406
RUN
IN
†
22pF
C
600mA
IN
C
**
4.7µF
CER
OUT
10µF
CER
1
5
V
FB
301k
GND
2
*MURATA LQH32CN2R2M33
**TAIYO YUDEN JMK316BJ106ML
† TAIYO YUDEN JMK212BJ475MG
66.5k
3406 TA13
100
V
V
= 5V
IN
OUT
V
OUT
= 3.3V
95
90
85
80
75
70
65
60
100mV/DIV
AC COUPLED
I
L
500mA/DIV
I
LOAD
500mA/DIV
3406 TA15
V
V
LOAD
= 5V
20µs/DIV
IN
= 3.3V
OUT
I
= 200mA TO 600mA
0.1
1
10
100
1000
OUTPUT CURRENT (mA)
3406 TA14
3406fa
14
LTC3406
LTC3406-1.5/LTC3406-1.8
U
PACKAGE DESCRIPTIO
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
3406fa
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no represen-
tationthattheinterconnectionofitscircuitsasdescribedhereinwillnotinfringeonexistingpatentrights.
15
LTC3406
LTC3406-1.5/LTC3406-1.8
U
TYPICAL APPLICATIO
Single Li-Ion 1.8V/600mA Regulator for Low Output Ripple and Small Footprint
4.7µH*
V
IN
4
1
3
V
OUT
1.8V
2.7V
V
SW
IN
C
**
TO 4.2V
IN
LTC3406-1.8
RUN
+
4.7µF
†
C
OUT1
100µF
CER
5
V
OUT
GND
3406 TA01
2
*MURATA LQH32CN4R7M34
**TAIYO YUDEN CERAMIC JMK212BJ475MG
†
SANYO POSCAP 4TPB100M
95
90
85
80
75
70
65
60
V
V
= 1.8V
OUT
OUT
V
OUT
100mV/DIV
100mV/DIV
AC COUPLED
AC COUPLED
V
= 2.7V
IN
= 3.6V
V
IN
I
L
I
L
500mA/DIV
500mA/DIV
V
IN
= 4.2V
I
LOAD
500mA/DIV
I
LOAD
500mA/DIV
3406 TA04
3406 TA03
V
V
LOAD
= 3.6V
40µs/DIV
IN
V
V
LOAD
= 3.6V
40µs/DIV
IN
= 1.8V
OUT
= 1.8V
OUT
I
= 200mA TO 600mA
I
= 0mA TO 600mA
0.1
1
10
100
1000
OUTPUT CURRENT (mA)
3406 TA02
RELATED PARTS
PART NUMBER
DESCRIPTION
COMMENTS
V : 3V to 18V, Constant Off-Time, I = 10µA, MS8 Package
LTC1474/LTC1475
250mA (I ) Low Quiescent Current Step-Down
OUT
IN
Q
DC/DC Converters
LT1616
1.4MHz, 600mA Step-Down DC/DC Converter
V : 3.6V to 25V, I = 1.9mA, ThinSOT Package
IN Q
LTC1701
LTC1767
LTC1779
LTC1875
LTC1877
LTC1878
LTC1879
LTC3404
1MHz, 500mA (I ) Step-Down DC/DC Converter
V : 2.5V to 5.5V, Constant Off-Time, I = 135µA, ThinSOT Package
IN Q
OUT
1.5A, 1.25MHz Step-Down Switching Regulator
V : 3V to 25V, I = 1mA, MS8/E Packages
IN Q
550kHz, 250mA (I ) Step-Down Switching Regulator
V : 2.5V to 9.8V, I = 135µA, ThinSOT Package
IN Q
OUT
550kHz, 1.2A (I ) Synchronous Step-Down Regulator
V : 2.7V to 6V, I = 15µA, TSSOP-16 Package
IN Q
OUT
550kHz, 600mA (I ) Synchronous Step-Down Regulator
V : 2.65V to 10V, I = 10µA, MS8 Package
IN Q
OUT
550kHz, 600mA (I ) Synchronous Step-Down Regulator
V : 2.65V to 6V, I = 10µA, MS8 Package
IN Q
OUT
550kHz, 1.2A (I ) Synchronous Step-Down Regulator
V : 2.7V to 10V, I = 15µA, TSSOP-16 Package
IN Q
OUT
1.4MHz, 600mA (I ) Synchronous Monolithic
Up to 95% Efficiency, V : 2.65V to 6V, I = 10µA, MS8 Package
IN Q
OUT
Step-Down Regulator
LTC3405/LTC3405A 1.5MHz, 300mA (I ) Synchronous Monolithic
Up to 95% Efficiency, V : 2.5V to 5.5V, I = 20µA,
IN Q
Fixed Output Voltages Available, ThinSOT Package
OUT
LTC3405A-1.5
LTC3405A-1.8
Step-Down Regulators
LTC3406B
LTC3406B-1.5
LTC3406B-1.8
1.5MHz, 600mA (I ) Synchronous Monolithic
Up to 95% Efficiency, with Pulse Skipping Mode
Fixed Output Voltages Available, ThinSOT Package
OUT
Step-Down Regulators
LTC3411
4MHz, 1.25A (I ) Synchronous Monolithic
Up to 95% Efficiency, V : 2.5V to 5.5V, I = 60µA, MS Package
IN Q
OUT
Step-Down Regulator
LTC3412
4MHz, 2.5A (I ) Synchronous Monolithic
Up to 95% Efficiency, V : 2.5V to 5.5V, I = 60µA, TSSOP Package
IN Q
OUT
Step-Down Regulator
3406fa
LT/TP 0604 1K REV A • PRINTED IN USA
LinearTechnology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
16
●
●
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©LINEAR TECHNOLOGY CORPORATION 2002
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Linear
LTC3406BES5-1.5#TRMPBF
LTC3406B - 1.5MHz, 600mA Synchronous Step-Down Regulator in ThinSOT; Package: SOT; Pins: 5; Temperature Range: -40°C to 85°C
Linear
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