OUTPUT CURRENT (mA)
70
EFFICIENCY (%)
80
90
95
0.1 10 100 1000
3406 F01b
60
1
85
75
65
VIN = 2.7V
V
OUT
= 1.8V
VIN = 4.2V
VIN = 3.6V
查询LTC3406-1.5供应商
FEATURES
■
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
■
Overtemperature Protected
■
Low Profile (1mm) ThinSOTTM Package
U
APPLICATIO S
■
Cellular Telephones
■
Personal Information Appliances
■
Wireless and DSL Modems
■
Digital Still Cameras
■
MP3 Players
■
Portable Instruments
LTC34 0 6
LTC34 06 -1.5/LTC 3 4 0 6-1. 8
1.5MHz, 600mA
Synchronous Step-Down
Regulator in ThinSOT
U
DESCRIPTIO
®
The LTC
nous buck regulator using a constant frequency, current
mode architecture. The device is available in an adjustable
version and fixed output voltages of 1.5V and 1.8V. 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-powered applications. 100% duty cycle provides low dropout
operation, extending battery life in portable systems.
Automatic Burst Mode
light loads, further extending battery life.
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 LTC3406 is available in a low
profile (1mm) ThinSOT package.
, 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.
Protected by U.S. Patents, including 6580258, 5481178.
3406 is a high efficiency monolithic synchro-
®
operation increases efficiency at
TYPICAL APPLICATIO
V
IN
2.7V
TO 5.5V
Figure 1a. High Efficiency Step-Down Converter
4
CIN**
4.7µF
CER
1
*
MURATA LQH32CN2R2M33
**
TAIYO YUDEN JMK212BJ475MG
†
TAIYO YUDEN JMK316BJ106ML
V
IN
LTC3406-1.8
V
RUN
GND
2
SW
OUT
3
5
2.2µH*
U
3406 F01a
C
OUT
10µF
CER
†
V
OUT
1.8V
600mA
Figure 1b. Efficiency vs Load Current
3406fa
1
LTC34 0 6
LTC34 06 -1.5/LTC 3 4 06 -1.8
WWWU
ABSOLUTE AXI U RATI GS
(Note 1)
Input Supply Voltage .................................. – 0.3V to 6V
RUN, VFB Voltages ..................................... – 0.3V to V
SW Voltage .................................. – 0.3V to (VIN + 0.3V)
P-Channel Switch Source Current (DC) ............. 800mA
N-Channel Switch Sink Current (DC) ................. 800mA
UU
W
Peak SW Sink and Source Current ........................ 1.3A
Operating Temperature Range (Note 2) .. –40°C to 85°C
IN
Junction Temperature (Note 3)............................ 125°C
Storage Temperature Range ................ –65°C to 150°C
Lead Temperature (Soldering, 10 sec)................. 300°C
PACKAGE/ORDER I FOR ATIO
ORDER PART
TOP VIEW
RUN 1
GND 2
SW 3
S5 PACKAGE
5-LEAD PLASTIC TSOT-23
T
= 125°C, θJA = 250°C/ W, θJC = 90°C/ W
JMAX
Consult LTC Marketing for parts specified with wider operating temperature ranges.
5 V
4 V
FB
IN
NUMBER
LTC3406ES5
S5 PART MARKING
LTA5
TOP VIEW
RUN 1
GND 2
SW 3
S5 PACKAGE
5-LEAD PLASTIC TSOT-23
T
= 125°C, θJA = 250°C/ W, θJC = 90°C/ W
JMAX
5 V
4 V
OUT
IN
ORDER PART
NUMBER
LTC3406ES5-1.5
LTC3406ES5-1.8
S5 PART MARKING
LTD6
LTC4
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
VFB
V
FB
∆V
FB
V
OUT
∆V
OUT
I
PK
V
LOADREG
V
IN
I
S
f
OSC
R
PFET
R
NFET
I
LSW
Feedback Current ● ±30 nA
Regulated Feedback Voltage LTC3406 (Note 4) TA = 25°C 0.5880 0.6 0.6120 V
LTC3406 (Note 4) 0°C T
LTC3406 (Note 4) –40°C ≤ T
Reference Voltage Line Regulation VIN = 2.5V to 5.5V (Note 4) ● 0.04 0.4 %/V
Regulated Output Voltage LTC3406-1.5, I
LTC3406-1.8, I
Output Voltage Line Regulation VIN = 2.5V to 5.5V ● 0.04 0.4 %/V
Peak Inductor Current VIN = 3V, VFB = 0.5V or V
Duty Cycle < 35%
Output Voltage Load Regulation 0.5 %
Input Voltage Range ● 2.5 5.5 V
Input DC Bias Current (Note 5)
Active Mode V
Sleep Mode V
Shutdown V
Oscillator Frequency VFB = 0.6V or V
R
of P-Channel FET ISW = 100mA 0.4 0.5 Ω
DS(ON)
R
of N-Channel FET ISW = –100mA 0.35 0.45 Ω
DS(ON)
SW Leakage V
= 0.5V or V
FB
= 0.62V or V
FB
= 0V, VIN = 4.2V 0.1 1 µA
RUN
= 0V or V
V
FB
= 0V, VSW = 0V or 5V, VIN = 5V ±0.01 ±1 µA
RUN
OUT
OUT
OUT
OUT
OUT
≤ 85°C 0.5865 0.6 0.6135 V
A
≤ 85°C ● 0.5850 0.6 0.6150 V
A
= 100mA ● 1.455 1.500 1.545 V
= 100mA ● 1.746 1.800 1.854 V
= 90%, 0.75 1 1.25 A
OUT
= 90%, I
= 103%, I
OUT
= 100% ● 1.2 1.5 1.8 MHz
= 0V 210 kHz
= 0A 300 400 µA
LOAD
= 0A 20 35 µA
LOAD
3406fa
2
LTC34 0 6
LTC34 06 -1.5/LTC 3 4 0 6-1. 8
ELECTRICAL CHARACTERISTICS
The ● denotes specifications which apply over the full operating temperature range, otherwise specifications are TA = 25°C.
= 3.6V unless otherwise specified.
V
IN
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
V
I
RUN
RUN
RUN Threshold ● 0.3 1 1.5 V
RUN Leakage Current ● ±0.01 ±1 µA
Note 1: Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
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.
Note 3: T
dissipation P
Note 4: The LTC3406 is tested in a proprietary test mode that connects
V
Note 5: Dynamic supply current is higher due to the gate charge being
is calculated from the ambient temperature TA and power
J
LTC3406: T
to the output of the error amplifier.
FB
delivered at the switching frequency.
UW
TYPICAL PERFOR A CE CHARACTERISTICS
(From Figure1a Except for the Resistive Divider Resistor Values)
Efficiency vs Input Voltage
100
I
95
90
85
80
75
70
EFFICIENCY (%)
65
60
55
50
= 100mA
OUT
I
= 1mA
OUT
I
= 600mA
OUT
I
= 0.1mA
OUT
V
= 1.8V
OUT
2
3
4
INPUT VOLTAGE (V)
I
OUT
= 10mA
5
6
3406 G01
Efficiency vs Output Current
95
V
= 1.2V
OUT
90
85
80
75
EFFICIENCY (%)
70
65
60
0.1 10 100 1000
VIN = 2.7V
VIN = 4.2V
VIN = 3.6V
1
OUTPUT CURRENT (mA)
according to the following formula:
D
= TA + (PD)(250°C/W)
J
Efficiency vs Output Current
95
V
= 1.5V
OUT
90
VIN = 2.7V
3406 G02
85
80
75
EFFICIENCY (%)
70
65
60
0.1 10 100 1000
VIN = 4.2V
VIN = 3.6V
1
OUTPUT CURRENT (mA)
3406 G03
Efficiency vs Output Current
100
V
= 2.5V
OUT
95
VIN = 2.7V
90
85
80
75
EFFICIENCY (%)
70
65
60
0.1 10 100 1000
VIN = 3.6V
VIN = 4.2V
1
OUTPUT CURRENT (mA)
3406 G04
Reference Voltage vs
Temperature
0.614
VIN = 3.6V
0.609
0.604
0.599
0.594
REFERENCE VOLTAGE (V)
0.589
0.584
–50
–25 0
TEMPERATURE (°C)
50 100 125
25 75
3406 G05
Oscillator Frequency vs
Temperature
1.70
VIN = 3.6V
1.65
1.60
1.55
1.50
1.45
FREQUENCY (MHz)
1.40
1.35
1.30
–50
–25 0
TEMPERATURE (°C)
50 100 125
25 75
3406 G06
3406fa
3
LTC34 0 6
INPUT VOLTAGE (V)
10
0.4
0.5
0.7
46
3406 G09
0.3
0.2
23
57
0.1
0
0.6
R
DS(ON)
(Ω)
MAIN
SWITCH
SYNCHRONOUS
SWITCH
LTC34 06 -1.5/LTC 3 4 06 -1.8
UW
TYPICAL PERFOR A CE CHARACTERISTICS
(From Figure1a Except for the Resistive Divider Resistor Values)
Oscillator Frequency vs
Supply Voltage
1.8
1.7
1.6
1.5
1.4
OSCILLATOR FREQUENCY (MHz)
1.3
1.2
0.7
0.6
0.5
0.4
(Ω)
0.3
DS(ON)
R
0.2
0.1
0
2
R
–50
34 56
SUPPLY VOLTAGE (V)
vs Temperature Supply Current vs Supply Voltage Supply Current vs Temperature
DS(ON)
VIN = 4.2V
MAIN SWITCH
SYNCHRONOUS SWITCH
–25 0
VIN = 3.6V
25 75
TEMPERATURE (°C)
3406 G07
VIN = 2.7V
50 100 125
3406 G10
Output Voltage vs Load Current
1.844
VIN = 3.6V
1.834
1.824
1.814
1.804
1.794
OUTPUT VOLTAGE (V)
1.784
1.774
100 900
0
200 300 400 500 600 700 800
LOAD CURRENT (mA)
50
V
= 1.8V
OUT
45
40
35
30
25
20
15
SUPPLY CURRENT (µA)
10
= 0A
I
LOAD
5
0
2
3
4
SUPPLY VOLTAGE (V)
R
) vs Input Voltage
DS(ON
3406 G08
50
VIN = 3.6V
45
= 1.8V
V
OUT
= 0A
I
LOAD
40
35
30
25
20
15
SUPPLY CURRENT (µA)
10
5
0
5
6
3406 G11
–50
–25
0
TEMPERATURE (°C)
50
25
75
100
125
3406 G12
300
250
200
150
100
SWITCH LEAKAGE (nA)
4
Switch Leakage vs Temperature
VIN = 5.5V
RUN = 0V
50
SYNCHRONOUS SWITCH
0
–50
–25 0
TEMPERATURE (°C)
MAIN SWITCH
50 100 125
25 75
3406 G13
Switch Leakage vs Input Voltage
120
RUN = 0V
100
80
60
40
SWITCH LEAKAGE (pA)
20
0
0
SYNCHRONOUS
234
1
INPUT VOLTAGE (V)
SWITCH
MAIN
SWITCH
56
3406 G14
SW
5V/DIV
V
OUT
100mV/DIV
AC COUPLED
200mA/DIV
Burst Mode Operation
I
L
V
I
LOAD
OUT
= 1.8V
= 50mA
4µs/DIVVIN = 3.6V
3406 G15
3406fa
UW
TYPICAL PERFOR A CE CHARACTERISTICS
(From Figure 1a Except for the Resistive Divider Resistor Values)
LTC34 0 6
LTC34 06 -1.5/LTC 3 4 0 6-1. 8
RUN
2V/DIV
V
OUT
2V/DIV
I
LOAD
500mA/DIV
Start-Up from Shutdown
IN
V
OUT
I
LOAD
= 3.6V
= 1.8V
= 600mA
40µs/DIVV
Load Step
V
OUT
100mV/DIV
AC COUPLED
I
L
500mA/DIV
I
LOAD
500mA/DIV
3406 G16
V
OUT
100mV/DIV
AC COUPLED
500mA/DIV
I
LOAD
500mA/DIV
Load Step
I
L
= 3.6V
IN
V
OUT
I
LOAD
= 1.8V
= 0mA TO 600mA
20µs/DIVV
V
OUT
100mV/DIV
AC COUPLED
500mA/DIV
I
LOAD
500mA/DIV
3406 G17
Load Step
I
L
V
OUT
100mV/DIV
AC COUPLED
500mA/DIV
I
LOAD
500mA/DIV
Load Step
I
L
= 3.6V
IN
= 1.8V
V
OUT
I
LOAD
20µs/DIVV
= 50mA TO 600mA
3406 G18
3406 G19
U
= 3.6V
IN
V
= 1.8V
OUT
= 100mA TO 600mA
I
LOAD
20µs/DIVV
UU
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.
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.
= 3.6V
IN
= 1.8V
V
OUT
= 200mA TO 600mA
I
LOAD
20µs/DIVV
3406 G20
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 feedback voltage from an external resistive divider across the
output.
V
(Pin 5) (LTC3406-1.5/LTC3406-1.8): Output Volt-
OUT
age Feedback Pin. An internal resistive divider divides the
output voltage down for comparison to the internal reference voltage.
3406fa
5
LTC34 0 6
LTC34 06 -1.5/LTC 3 4 06 -1.8
U
U
W
FU CTIO AL DIAGRA
SLOPE
COMP
+
EA
–
VFB/V
OUT
5
R1 + R2 = 550k
LTC3406-1.8
R1 + R2 = 540k
RUN
1
R1LTC3406-1.5
R2
V
IN
0.6V REF
FB
SHUTDOWN
OSC
FREQ
SHIFT
0.6V
0.65V
OSC
V
4
3406 BD
IN
SW
3
GND
2
–
+
0.4V
–
+
BURST
Q
S
R
Q
RS LATCH
SLEEP
SWITCHING
LOGIC
AND
BLANKING
CIRCUIT
–
I
COMP
ANTI-
SHOOT-
THRU
I
RCMP
+
+
–
5Ω
U
OPERATIO
Main Control Loop
The LTC3406 uses a constant frequency, current mode
step-down architecture. Both the main (P-channel
MOSFET) and synchronous (N-channel MOSFET) 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
current at which I
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 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
the beginning of the next clock cycle.
COMP
(Refer to Functional Diagram)
, resets the RS latch. The peak inductor
resets the RS latch, is controlled by
COMP
, or
RCMP
Burst Mode Operation
The LTC3406 is capable of Burst Mode operation in which
the internal power MOSFETs operate intermittently based
on load demand.
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
intervals at moderate loads. In between these burst events,
the power MOSFETs and any unneeded circuitry are turned
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 signaling the BURST comparator to trip and turn the top MOSFET
on. This process repeats at a rate that is dependent on the
load demand.
6
3406fa
OPERATIO
LTC34 0 6
LTC34 06 -1.5/LTC 3 4 0 6-1. 8
U
(Refer to Functional Diagram)
Short-Circuit Protection
When the output is shorted to ground, the frequency of the
oscillator is reduced to about 210kHz, 1/7 the nominal
frequency. This frequency foldback ensures that the inductor current has more time to decay, thereby preventing
runaway. The oscillator’s frequency will progressively
increase to 1.5MHz when V
FB
or V
rises above 0V.
OUT
Dropout Operation
As the input supply voltage decreases to a value approaching 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
of the P-channel switch increases
DS(ON)
(see Typical Performance Characteristics). Therefore, the
user should calculate the power dissipation when the
LTC3406 is used at 100% duty cycle with low input voltage
(See Thermal Considerations in the Applications Information section).
in the maximum output current as a function of input
voltage for various output voltages.
Slope Compensation and Inductor Peak Current
Slope compensation provides stability in constant frequency architectures by preventing subharmonic oscillations 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 compensating ramp, which allows the maximum inductor peak
current to remain unaffected throughout all duty cycles.
1200
1000
V
= 1.8V
OUT
800
V
= 1.5V
OUT
600
400
200
MAXIMUM OUTPUT CURRENT (mA)
V
= 2.5V
OUT
Low Supply Operation
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
0
2.5
Figure 2. Maximum Output Current vs Input Voltage
3.5 4.0 4.5
3.0
SUPPLY VOLTAGE (V)
5.0 5.5
3406 F02
3406fa
7
LTC34 0 6
CI
VVV
V
IN OMAX
OUT IN OUT
IN
required I
RMS
≅
−
()
[]
12/
LTC34 06 -1.5/LTC 3 4 06 -1.8
WUUU
APPLICATIO S I FOR ATIO
The basic LTC3406 application circuit is shown in Figure 1.
External component selection is driven by the load requirement and begins with the selection of L followed by C
C
.
OUT
IN
and
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 VIN or V
also increases the ripple
OUT
current as shown in equation 1. A reasonable starting point
for setting ripple current is ∆IL = 240mA (40% of 600mA).
∆ =
I
1
L OUT
fL
()( )
⎛
1
V
−
⎜
⎝
V
OUT
V
IN
⎞
⎟
⎠
(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.
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.
Inductor Core Selection
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 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 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.
Table 1. Representative Surface Mount Inductors
PART VALUE DCR MAX DC SIZE
NUMBER (µH) (Ω MAX) CURRENT (A) W × L × H (mm
Sumida 1.5 0.043 1.55 3.8 × 3.8 × 1.8
CDRH3D16 2.2 0.075 1.20
3.3 0.110 1.10
4.7 0.162 0.90
Sumida 2.2 0.116 0.950 3.5 × 4.3 × 0.8
CMD4D06 3.3 0.174 0.770
4.7 0.216 0.750
Panasonic 3.3 0.17 1.00 4.5 × 5.4 × 1.2
ELT5KT 4.7 0.20 0.95
Murata 1.0 0.060 1.00 2.5 × 3.2 × 2.0
LQH32CN 2.2 0.097 0.79
4.7 0.150 0.65
CIN and C
Selection
OUT
3
)
In continuous mode, the source current of the top MOSFET
is a square wave of duty cycle V
OUT/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:
This formula has a maximum at VIN = 2V
I
RMS
= I
/2. This simple worst-case condition is com-
OUT
OUT
, where
monly used for design because even significant deviations
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
temperature than required. Always consult the manufacturer if there is any question.
8
3406fa
WUUU
APPLICATIO S I FOR ATIO
LTC34 0 6
LTC34 06 -1.5/LTC 3 4 0 6-1. 8
The selection of C
is driven by the required effective
OUT
series resistance (ESR).
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 ∆V
is deter-
OUT
mined by:
∆≅∆ +
V I ESR
OUT L
⎛
⎜
⎝
8
where f = operating frequency, C
fC
1
OUT
⎞
⎟
⎠
= output capacitance
OUT
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.
Aluminum electrolytic and dry tantalum capacitors are
both 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.
Using Ceramic Input and Output Capacitors
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.
When choosing the input and output ceramic capacitors,
choose the X5R or X7R dielectric formulations. These
dielectrics have the best temperature and voltage characteristics of all the ceramics for a given value and size.
Output Voltage Programming (LTC3406 Only)
In the adjustable version, the output voltage is set by a
resistive divider according to the following formula:
R
2
VV
=+
OUT
⎛
06 1
.
⎜
⎝
⎞
⎟
⎠
R
1
(2)
The external resistive divider is connected to the output,
allowing remote voltage sensing as shown in Figure 3.
LTC3406
V
GND
0.6V ≤ V
FB
OUT
≤ 5.5V
R2
R1
3406 F03
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.
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
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
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 + ...)
where L1, L2, etc. are the individual losses as a percentage
of input power.
3406fa
9
LTC34 0 6
LTC34 06 -1.5/LTC 3 4 06 -1.8
WUUU
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.
1
0.1
0.01
0.001
POWER LOSS (W)
0.0001
0.00001
V
= 1.2V
OUT
= 1.5V
V
OUT
= 1.8V
V
OUT
= 2.5V
V
OUT
0.1 1
Figure 4. Power Lost vs Load Current
10 100 1000
LOAD CURRENT (mA)
3406 F04
1. The VIN quiescent current is due to two components:
the DC bias current as given in the electrical characteristics 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/dt is the current out of V
the DC bias current. In continuous mode, I
that is typically larger than
IN
GATECHG
=
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.
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 R
and the duty cycle
DS(ON)
(DC) as follows:
R
The R
= (R
SW
DS(ON)
DS(ON)TOP
for both the top and bottom MOSFETs can
)(DC) + (R
DS(ON)BOT
)(1 – DC)
be obtained from the Typical Performance Charateristics
curves. Thus, to obtain I2R losses, simply add RSW to
RL and multiply the result by the square of the average
output current.
Other losses including CIN and C
ESR dissipative
OUT
losses and inductor core losses generally account for less
than 2% total additional loss.
Thermal Considerations
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 temperature 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 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 temperature rise is given by:
TR = (PD)(θJA)
where PD is the power dissipated by the regulator and θ
JA
is the thermal resistance from the junction of the die to the
ambient temperature.
10
3406fa
WUUU
APPLICATIO S I FOR ATIO
LTC34 0 6
LTC34 06 -1.5/LTC 3 4 0 6-1. 8
The junction temperature, TJ, is given by:
= TA + T
T
J
R
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 performance graph of switch resistance, the R
DS(ON)
of the
P-channel switch at 70°C is approximately 0.52Ω. Therefore, power dissipated by the part is:
LOAD
2
• R
DS(ON)
= 187.2mW
PD = I
For the SOT-23 package, the θJA is 250°C/W. Thus, the
junction temperature of the regulator is:
TJ = 70°C + (0.1872)(250) = 116.8°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)
).
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 parallel
with C
, causing a rapid drop in V
OUT
. No regulator can
OUT
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
LTC3406. These items are also illustrated graphically in
Figures 5 and 6. Check the following in your layout:
1. The power traces, consisting of the GND trace, the SW
trace and the VIN trace should be kept short, direct and
wide.
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
equal to (∆I
resistance of C
discharge C
• ESR), where ESR is the effective series
LOAD
OUT
, which generates a feedback error signal.
OUT
The regulator loop then acts to return V
state value. During this recovery time V
immediately shifts by an amount
OUT
. ∆I
also begins to charge or
LOAD
to its steady-
OUT
can be moni-
OUT
tored for overshoot or ringing that would indicate a stability
problem. For a detailed explanation of switching control
loop theory, see Application Note 76.
2. Does the VFB pin connect directly to the feedback
resistors? The resistive divider R1/R2 must be connected between the (+) plate of C
3. Does the (+) plate of C
connect to VIN as closely as
IN
and ground.
OUT
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. Keep the (–) plates of CIN and C
as close as possible.
OUT
3406fa
11
LTC34 0 6
LTC34 06 -1.5/LTC 3 4 06 -1.8
WUUU
APPLICATIO S I FOR ATIO
1
RUN
LTC3406
2
–
V
C
OUT
OUT
+
L1
BOLD LINES INDICATE HIGH CURRENT PATHS
GND
3
SW
Figure 5a. LTC3406 Layout Diagram
VIA TO V
PIN 1
V
OUT
SW
L1
LTC3406
5
V
FB
C
FWD
3406 F05a
R1
–
V
OUT
+
V
IN
BOLD LINES INDICATE HIGH CURRENT PATHS
R2
4
V
IN
C
IN
1
RUN
LTC3406-1.8
2
GND
C
OUT
3
L1
SW
5
V
OUT
4
V
IN
C
IN
V
IN
3406 F05b
Figure 5b. LTC3406-1.8 Layout Diagram
VIA TO GND
R1
IN
R2
C
FWD
V
IN
VIA TO V
OUT
PIN 1
V
OUT
SW
L1
LTC3406-1.8
VIA TO V
VIA TO V
IN
OUT
V
IN
C
OUT
GND
C
IN
3406 F06a
Figure 6a. LTC3406 Suggested Layout
Design Example
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
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),
L
1
=
fI
()∆()
⎛
V
OUT
L
−
1
⎜
⎝
V
OUT
V
IN
⎞
⎟
⎠
(3)
C
OUT
GND
C
IN
3406 F06b
Figure 6b. LTC3406-1.8 Suggested Layout
Substituting V
OUT
= 2.5V, V
= 4.2V, ∆IL = 240mA and
IN
f = 1.5MHz in equation (3) gives:
V
25
L
1 5 240
.
MHz mA
.( )..
⎛
1
⎜
⎝
25
42
V
⎞
=µ
281
⎟
⎠
V
H= −
.
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
LOAD(MAX)
/2 at temperature and C
will require an ESR
OUT
of less than 0.25Ω. In most cases, a ceramic capacitor will
satisfy this requirement.
12
3406fa
WUUU
APPLICATIO S I FOR ATIO
LTC34 0 6
LTC34 06 -1.5/LTC 3 4 0 6-1. 8
For the feedback resistors, choose R1 = 316k. R2 can
then be calculated from equation (2) to be:
R
2
2.7V
TO 4.2V
⎛
OUT
⎜
⎝
06
V
IN
⎞
Rk
1 1 1000= −
=
⎟
⎠
.
2.2µH*
4
V
C
IN
2.2µF
CER
†
IN
LTC3406
1
RUN
GND
*MURATA LQH32CN2R2M33
** TAIYO YUDEN JMK316BJ106ML
†
TAIYO YUDEN LMK212BJ225MG
3
SW
V
FB
2
22pF
5
1M
316k
3406 F07a
C
OUT
10µF
CER
**
V
OUT
2.5V
V
Figure 7a
U
TYPICAL APPLICATIO S
Figure 7 shows the complete circuit along with its efficiency curve.
100
V
= 2.5V
OUT
95
VIN = 2.7V
90
85
80
75
EFFICIENCY (%)
70
65
60
0.1 10 100 1000
VIN = 3.6V
VIN = 4.2V
1
OUTPUT CURRENT (mA)
3406 F07b
Figure 7b
95
V
= 1.5V
OUT
90
VIN = 2.7V
85
80
75
EFFICIENCY (%)
70
65
60
0.1 10 100 1000
VIN = 4.2V
VIN = 3.6V
1
OUTPUT CURRENT (mA)
3406 TA06
Single Li-Ion 1.5V/600mA Regulator for
High Efficiency and Small Footprint
V
IN
2.7V
TO 4.2V
100mV/DIV
AC COUPLED
500mA/DIV
500mA/DIV
V
I
LOAD
OUT
CIN**
4.7µF
CER
I
L
V
I
LOAD
4
V
1
RUN
= 3.6V
IN
= 1.5V
OUT
= 0A TO 600mA
IN
LTC3406-1.5
V
GND
2
20µs/DIVV
SW
OUT
**
2.2µH*
3
†
C
OUT1
10µF
5
3406 TA05
MURATA LQH32CN2R2M33
*
TAIYO YUDEN JMK212BJ475MG
†
TAIYO YUDEN JMK316BJ106ML
CER
100mV/DIV
AC COUPLED
500mA/DIV
500mA/DIV
3406 TA07
V
1.5V
V
I
LOAD
OUT
OUT
I
L
= 3.6V
IN
= 1.5V
V
OUT
I
LOAD
20µs/DIVV
= 200mA TO 600mA
3406 TA08
3406fa
13
LTC34 0 6
LTC34 06 -1.5/LTC 3 4 06 -1.8
U
TYPICAL APPLICATIO S
Single Li-Ion 1.2V/600mA Regulator for High Efficiency and Small Footprint
95
V
= 1.2V
OUT
90
85
80
75
EFFICIENCY (%)
70
65
60
0.1 10 100 1000
VIN = 2.7V
VIN = 4.2V
VIN = 3.6V
1
OUTPUT CURRENT (mA)
3406 TA10
V
IN
2.7V
TO 4.2V
100mV/DIV
AC COUPLED
500mA/DIV
500mA/DIV
V
I
LOAD
OUT
I
C
2.2µF
CER
L
4
†
IN
1
= 3.6V
IN
= 1.2V
V
OUT
= 0mA TO 600mA
I
LOAD
V
IN
LTC3406
RUN
GND
2.2µH*
3
SW
V
FB
2
20µs/DIVV
22pF
5
301k
*MURATA LQH32CN2R2M33
301k
** TAIYO YUDEN JMK316BJ106ML
†
TAIYO YUDEN LMK212BJ225MG
3406 TA09
3406 TA11
V
1.2V
C
**
OUT
10µF
CER
V
OUT
100mV/DIV
AC COUPLED
500mA/DIV
I
LOAD
500mA/DIV
OUT
I
L
= 3.6V
IN
V
OUT
I
LOAD
= 1.2V
20µs/DIVV
= 200mA TO 600mA
3406 TA12
V
IN
5V
100
VIN = 5V
= 3.3V
V
OUT
95
90
85
80
75
EFFICIENCY (%)
70
65
60
0.1 10 100 1000
1
OUTPUT CURRENT (mA)
C
IN
4.7µF
CER
†
Tiny 3.3V/600mA Buck Regulator
2.2µH*
4
1
V
IN
LTC3406
RUN
3406 TA14
GND
3
SW
V
FB
2
22pF
5
301k
*MURATA LQH32CN2R2M33
66.5k
** TAIYO YUDEN JMK316BJ106ML
†
TAIYO YUDEN JMK212BJ475MG
3406 TA13
V
OUT
100mV/DIV
AC COUPLED
I
500mA/DIV
I
LOAD
500mA/DIV
C
**
OUT
10µF
CER
L
= 5V
IN
= 3.3V
V
OUT
= 200mA TO 600mA
I
LOAD
V
OUT
3.3V
600mA
20µs/DIVV
3406 TA15
3406fa
14
PACKAGE DESCRIPTIO
LTC34 0 6
LTC34 06 -1.5/LTC 3 4 0 6-1. 8
U
S5 Package
5-Lead Plastic TSOT-23
(Reference LTC DWG # 05-08-1635)
0.62
MAX
3.85 MAX
0.20 BSC
DATUM ‘A’
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
2.62 REF
RECOMMENDED SOLDER PAD LAYOUT
PER IPC CALCULATOR
0.30 – 0.50 REF
0.95
REF
1.22 REF
1.4 MIN
0.09 – 0.20
(NOTE 3)
2.80 BSC
1.50 – 1.75
(NOTE 4)
0.80 – 0.90
1.00 MAX
PIN ONE
0.95 BSC
2.90 BSC
(NOTE 4)
1.90 BSC
0.30 – 0.45 TYP
5 PLCS (NOTE 3)
0.01 – 0.10
S5 TSOT-23 0302
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 representation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
3406fa
15
LTC34 0 6
LTC34 06 -1.5/LTC 3 4 06 -1.8
U
TYPICAL APPLICATIO
Single Li-Ion 1.8V/600mA Regulator for Low Output Ripple and Small Footprint
95
V
= 1.8V
OUT
90
85
80
75
EFFICIENCY (%)
70
65
60
VIN = 4.2V
0.1 10 100 1000
VIN = 2.7V
VIN = 3.6V
1
OUTPUT CURRENT (mA)
3406 TA02
V
IN
2.7V
TO 4.2V
100mV/DIV
AC COUPLED
500mA/DIV
500mA/DIV
V
I
LOAD
OUT
CIN**
4.7µF
CER
I
L
4
1
= 3.6V
IN
= 1.8V
V
OUT
= 0mA TO 600mA
I
LOAD
V
IN
LTC3406-1.8
RUN
GND
2
40µs/DIVV
4.7µH*
3
SW
+
C
OUT1
5
V
OUT
3406 TA01
MURATA LQH32CN4R7M34
*
TAIYO YUDEN CERAMIC JMK212BJ475MG
**
†
SANYO POSCAP 4TPB100M
100µF
3406 TA03
V
OUT
1.8V
†
V
OUT
100mV/DIV
AC COUPLED
500mA/DIV
I
LOAD
500mA/DIV
I
L
= 3.6V
IN
= 1.8V
V
OUT
I
LOAD
40µs/DIVV
= 200mA TO 600mA
3406 TA04
RELATED PARTS
PART NUMBER DESCRIPTION COMMENTS
LTC1474/LTC1475 250mA (I
DC/DC Converters
LT1616 1.4MHz, 600mA Step-Down DC/DC Converter VIN: 3.6V to 25V, IQ = 1.9mA, ThinSOT Package
LTC1701 1MHz, 500mA (I
LTC1767 1.5A, 1.25MHz Step-Down Switching Regulator VIN: 3V to 25V, IQ = 1mA, MS8/E Packages
LTC1779 550kHz, 250mA (I
LTC1875 550kHz, 1.2A (I
LTC1877 550kHz, 600mA (I
LTC1878 550kHz, 600mA (I
LTC1879 550kHz, 1.2A (I
LTC3404 1.4MHz, 600mA (I
Step-Down Regulator
LTC3405/LTC3405A 1.5MHz, 300mA (I
LTC3405A-1.5 Step-Down Regulators Fixed Output Voltages Available, ThinSOT Package
LTC3405A-1.8
LTC3406B 1.5MHz, 600mA (I
LTC3406B-1.5 Step-Down Regulators Fixed Output Voltages Available, ThinSOT Package
LTC3406B-1.8
LTC3411 4MHz, 1.25A (I
Step-Down Regulator
LTC3412 4MHz, 2.5A (I
Step-Down Regulator
Linear Technology Corporation
16
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 ● FAX: (408) 434-0507
) Low Quiescent Current Step-Down VIN: 3V to 18V, Constant Off-Time, IQ = 10µA, MS8 Package
OUT
) Step-Down DC/DC Converter VIN: 2.5V to 5.5V, Constant Off-Time, IQ = 135µA, ThinSOT Package
OUT
) Step-Down Switching Regulator VIN: 2.5V to 9.8V, IQ = 135µA, ThinSOT Package
OUT
) Synchronous Step-Down Regulator VIN: 2.7V to 6V, IQ = 15µA, TSSOP-16 Package
OUT
) Synchronous Step-Down Regulator VIN: 2.65V to 10V, IQ = 10µA, MS8 Package
OUT
) Synchronous Step-Down Regulator VIN: 2.65V to 6V, IQ = 10µA, MS8 Package
OUT
) Synchronous Step-Down Regulator VIN: 2.7V to 10V, IQ = 15µA, TSSOP-16 Package
OUT
) Synchronous Monolithic Up to 95% Efficiency, VIN: 2.65V to 6V, IQ = 10µA, MS8 Package
OUT
) Synchronous Monolithic Up to 95% Efficiency, VIN: 2.5V to 5.5V, IQ = 20µA,
OUT
) Synchronous Monolithic Up to 95% Efficiency, with Pulse Skipping Mode
OUT
) Synchronous Monolithic Up to 95% Efficiency, VIN: 2.5V to 5.5V, IQ = 60µA, MS Package
OUT
) Synchronous Monolithic Up to 95% Efficiency, VIN: 2.5V to 5.5V, IQ = 60µA, TSSOP Package
OUT
LT/TP 0604 1K REV A • PRINTED IN USA
●
www.linear.com
© LINEAR TECHNOLOGY CORPORATION 2002
3406fa
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