LINER LTC3419EDD-1

LTC3419
Dual Monolithic 600mA
Synchronous Step-Down
Regulator
DESCRIPTION
FEATURES
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High Efficiency Dual Step-Down Outputs: Up to 96%
600mA Current per Channel at VIN = 3V
Only 35μA Quiescent Current During Operation
(Both Channels)
2.25MHz Constant-Frequency Operation
2.5V to 5.5V Input Voltage Range
Low Dropout Operation: 100% Duty Cycle
No Schottky Diodes Required
Internally Compensated for All Ceramic Capacitors
Independent Internal Soft-Start for Each Channel
Available in Fixed Output Versions
Current Mode Operation for Excellent Line and Load
Transient Response
0.6V Reference Allows Low Output Voltages
User-Selectable Burst Mode® Operation
Short-Circuit Protected
Ultralow Shutdown Current: IQ < 1μA
Available in Small MSOP or 3mm × 3mm
DFN-8 Packages
APPLICATIONS
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Cellular Telephones
Digital Still Cameras
Wireless and DSL Modems
Portable Media Players
PDAs/Palmtop PCs
The LTC®3419 is a dual, 2.25MHz, constant-frequency,
synchronous step-down DC/DC converter in a tiny
3mm × 3mm DFN package. 100% duty cycle provides
low dropout operation, extending battery life in portable
systems. Low output voltages are supported with the 0.6V
feedback reference voltage. Each regulator can supply
600mA output current.
The input voltage range is 2.5V to 5.5V, making it ideal
for Li-Ion and USB powered applications. Supply current during operation is only 35μA and drops to <1μA in
shutdown. A user-selectable mode input allows the user
to trade off between high efficiency Burst Mode operation
and pulse-skipping mode.
An internally set 2.25MHz switching frequency allows the
use of tiny surface mount inductors and capacitors. Internal soft-start reduces inrush current during start-up. Both
outputs are internally compensated to work with ceramic
output capacitors. The LTC3419 is available in a low profile
(0.75mm) 3mm × 3mm DFN package. The LTC3419 is also
available in a fixed output voltage configuration selected
via internal resistor dividers (see Table 2).
, LT, LT, LTC and LTM are registered trademarks of Linear Technology Corporation.
Burst Mode 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, 6127815, 6304066, 6498466, 6580258, 6611131.
TYPICAL APPLICATION
Efficiency and Power Loss vs
Output Current
Dual Monolithic Buck Regulator in 8-Lead 3 × 3 DFN
100
80
10μF
SW2
3.3μH
SW1
22pF
22pF
VOUT1
2.5V AT
600mA
EFFICIENCY (%)
LTC3419
3.3μH
1
70
60
0.1
50
40
0.01
30
VFB2
10μF
118k
59k
GND
20
VFB1
59k
187k
10μF
3419 TA01
10
0
0.1
VOUT = 1.2V
VOUT = 1.8V
VOUT = 2.5V
1
10
100
OUTPUT CURRENT (mA)
POWER LOSS (W)
RUN2 VIN RUN1
MODE
VOUT2
1.8V AT
600mA
10
VIN = 3.6V
90
VIN
2.5V TO 5.5V
0.001
0.0001
1000
3419 TA01b
3419f
1
LTC3419
ABSOLUTE MAXIMUM RATINGS
(Note 1)
Input Supply Voltage (VIN) ............................. –0.3 to 6V
VFB1, VFB2 ........................................ –0.3V to VIN + 0.3V
RUN1, RUN2, MODE ........................ –0.3V to VIN + 0.3V
SW1, SW2 ....................................... –0.3V to VIN + 0.3V
P-Channel SW Source Current (DC) (Note 2).......800mA
N-Channel SW Source Current (DC) (Note 2) ......800mA
Peak SW Source and Sink Current (Note 2) .............1.3A
Operating Temperature Range (Note 3) .......–40 to 85°C
Junction Temperature (Note 6) ............................. 125°C
Storage Temperature Range...................–65°C to 125°C
Lead Temperature (Soldering, 10 sec)
MSOP Package ................................................. 300°C
PACKAGE/ORDER INFORMATION
TOP VIEW
VFB1 1
RUN1 2
MODE 3
9
SW1 4
TOP VIEW
8
VFB2
7
RUN2
6
SW2
5
VIN
VFB1
RUN1
MODE
SW1
GND
DD PART MARKING
LTC3419EDD
LTC3419EDD-1
VFB2
RUN2
SW2
VIN
GND
MS PACKAGE
10-LEAD PLASTIC MSOP
TJMAX = 125°C, θJA = 120°C/W
DD PACKAGE
8-LEAD (3mm × 3mm) PLASTIC DFN
TJMAX = 125°C, θJA = 40°C/W
EXPOSED PAD (PIN 9) IS GND, MUST BE SOLDERED TO PCB
ORDER PART NUMBER
10
9
8
7
6
1
2
3
4
5
ORDER PART NUMBER
MS PART MARKING
LTC3419EMS
LTC3419EMS-1
LTCQK
LTCWX
LCQJ
LCWW
Order Options Tape and Reel: Add #TR
Lead Free: Add #PBF Lead Free Tape and Reel: Add #TRPBF
Lead Free Part Marking: http://www.linear.com/leadfree/
Consult LTC Marketing for parts specified with wider operating temperature ranges.
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 noted.
SYMBOL
PARAMETER
CONDITIONS
MIN
●
TYP
2.5
MAX
UNITS
VIN
VIN Operating Voltage
5.5
V
VUV
VIN Undervoltage Lockout
VIN Low to High
●
2.1
2.5
V
IFB
Feedback Pin Input Current
LTC3419
LTC3419-1
●
●
3
±30
5
nA
μA
VFBREG1
Regulated Feedback Voltage (Channel 1) LTC3419, 0°C < TA < 85°C
LTC3419, –40°C < TA < 85°C
LTC3419-1, –40°C < TA < 85°C
●
●
0.590
0.588
1.544
0.600
0.600
1.575
0.610
0.612
1.606
V
V
V
VFBREG2
Regulated Feedback Voltage (Channel 2) LTC3419, 0°C < TA < 85°C
LTC3419, –40°C < TA < 85°C
LTC3419-1, –40°C < TA < 85°C
●
●
0.590
0.588
1.764
0.600
0.600
1.8
0.610
0.612
1.836
V
V
V
ΔVLINE REG
Reference Voltage Line Regulation
0.3
0.5
VIN = 2.5V to 5.5V (Note 7)
%/V
3419f
2
LTC3419
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 noted.
SYMBOL
PARAMETER
CONDITIONS
ΔVLOAD REG
Output Voltage Load Regulation
ILOAD = 0mA to 600mA (Note 7)
0.5
IS
Input DC Supply Current
Active Mode (Note 4)
Sleep Mode
Shutdown
VFB1 = VFB2 = 0.95 × VFBREG
VFB1 = VFB2 = 1.05 × VFBREG , VIN = 5.5V
RUN1 = RUN2 = 0V, VIN = 5.5V
500
35
0.1
700
60
1
μA
μA
μA
fOSC
Oscillator Frequency
VFB = VFBREG
1.8
2.25
2.7
MHz
ILIM
Peak Switch Current Limit
Channel 1 (600mA)
Channel 2 (600mA)
VIN = 3V, VFB < VFBREG , Duty Cycle < 35%
900
900
1200
1200
RDS(ON)
Channel 1 (Note 5)
Top Switch On-Resistance
Bottom Switch On-Resistance
Channel 2 (Note 5)
Top Switch On-Resistance
Bottom Switch On-Resistance
MIN
●
TYP
MAX
UNITS
%
mA
mA
VIN = 3.6V, ISW = 100mA
VIN = 3.6V, ISW = 100mA
0.4
0.4
0.6
0.6
Ω
Ω
VIN = 3.6V, ISW = 100mA
VIN = 3.6V, ISW = 100mA
0.4
0.4
0.6
0.6
Ω
Ω
0.01
1
μA
0.1
0.95
1.3
ms
0.4
1
1.2
V
0.01
1
μA
1
1.2
V
0.01
1
μA
ISW(LKG)
Switch Leakage Current
VIN = 5V, VRUN = 0V
tSOFTSTART
Soft-Start Time
VFB from 10% to 90% Full Scale
VRUN
RUN Threshold High
●
IRUN
RUN Leakage Current
●
VMODE
MODE Threshold High
●
IMODE
MODE Leakage Current
●
VBURST
Output Ripple in Burst Mode Operation
VOUT = 1.5V, COUT = 10μF
Note 1: Stresses beyond those listed under Absolute Maximum Ratings
may cause permanent damage to the device. Exposure to any Absolute
Maximum Rating condition for extended periods may affect device
reliability and lifetime.
Note 2: Guaranteed by long term current density limitations.
Note 3: The LTC3419E and LTC3419E-1 are guaranteed to meet specified
performance from 0°C to 85°C. Specifications over the –40°C and 85°C
operating temperature range are assured by design, characterization and
correlation with statistical process controls.
Note 4: Dynamic supply current is higher due to the internal gate charge
being delivered at the switching frequency.
0.4
20
mVP-P
Note 5: The DFN switch on-resistance is guaranteed by correlation to
wafer level measurements.
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: The converter is tested in a proprietary test mode that connects
the output of the error amplifier to the SW pin, which is connected to an
external servo loop.
3419f
3
LTC3419
TYPICAL PERFORMANCE CHARACTERISTICS
Burst Mode Operation
TA = 25°C, VIN = 3.6V, unless otherwise noted.
Pulse Skip Mode Operation
Efficiency vs Input Voltage
100
SW
2V/DIV
IOUT = 100mA
90
SW
2V/DIV
EFFICIENCY (%)
80
VOUT
50mV/DIV
AC-COUPLED
VOUT
50mV/DIV
AC-COUPLED
IL
100mA/DIV
IL
100mA/DIV
60
IOUT = 0.1mA
3419 G02
5μs/DIV
VIN = 3.6V
VOUT = 1.8V
ILOAD = 25mA
IOUT = 10mA
50
3419 G01
2μs/DIV
70
IOUT = 1mA
IOUT = 600mA
40
VIN = 3.6V
VOUT = 1.8V
ILOAD = 5mA
VOUT = 1.8V
30
3.0
3.5
2.5
4.0
VIN (V)
4.5
5.5
5.0
3419 G03
Reference Voltage
vs Temperature
Oscillator Frequency
vs Temperature
1.5
2.6
60
2.5
1.0
0
–0.5
VIN = 4.2V
2.3
SUPPLY CURRENT (μA)
FREQUENCY (MHz)
0.5
VIN = 3.6V
2.2
VIN = 2.7V
2.1
2.0
40
VIN = 5.5V
30
VIN = 2.7V
20
–1.0
1.9
–1.5
–50
–25
0
50
25
75
TEMPERATURE (°C)
100
1.8
–50
125
–25
25
75
0
50
TEMPERATURE (°C)
3419 G04
2.5
0.45
2.0
0.40
MAIN SWITCH
1.5
0.5
3.5
4.0
VIN (V)
4.5
5.0
5.5
0.5
0.35
3419 G07
0.20
2.5
75
100
0.6
3.0
3.5
4.0 4.5
VIN (V)
MAIN SWITCH
0.4
0.3
SYNCHRONOUS SWITCH
SYNCHRONOUS
SWITCH
0.2
0.25
3.0
25
0
50
TEMPERATURE (°C)
Switch On-Resistance vs
Temperature
MAIN SWITCH
0.30
SYNCHRONOUS
SWITCH
–25
3419 G06
RDS(ON) (Ω)
RDS(ON) (Ω)
0.50
0
2.5
10
–50
125
Switch On-Resistance vs
Input Voltage
3.0
1.0
100
3419 G05
Switch Leakage vs Input Voltage
LEAKAGE CURRENT (nA)
ILOAD = 0A
RUN1 = RUN2 = VIN
50
2.4
VFB (% ERROR)
Supply Current
vs Temperature
5.0
5.5
6.0
3419 G08
0.1
–50
VIN = 2.7V
VIN = 3.6V
VIN = 4.2V
–25
25
75
0
50
TEMPERATURE (°C)
100
125
3419 G09
3419f
4
LTC3419
TYPICAL PERFORMANCE CHARACTERISTICS
Efficiency vs Load Current
Efficiency vs Load Current
100
100
90
90
90
80
80
80
70
70
70
60
50
40
60
50
40
30
30
20
20
VIN = 2.7V
VIN = 3.6V
VIN = 4.2V
10
VOUT = 1.2V
0
0.1
10
100
1
OUTPUT CURRENT (mA)
EFFICIENCY (%)
100
EFFICIENCY (%)
EFFICIENCY (%)
Efficiency vs Load Current
VOUT = 1.8V
0
0.1
10
100
1
OUTPUT CURRENT (mA)
Efficiency vs Load Current
VOUT = 2.5V
0
0.1
10
100
1
OUTPUT CURRENT (mA)
1000
2.5
1000
3419 G12
Load Regulation
2.0
VOUT = 1.2V
VOUT = 1.8V
VOUT = 2.5V
Burst Mode OPERATION
VOUT = 1.8V
1.5
VOUT ERROR (%)
PULSE SKIP MODE
60
50
40
30
VOUT ERROR (%)
2.0
70
EFFICIENCY (%)
VIN = 2.7V
VIN = 3.6V
VIN = 4.2V
10
Load Regulation
3.0
80
1.5
Burst Mode OPERATION
1.0
0.5
1.0
0.5
0
0
20
–0.5
–0.5
10
VOUT = 1.8V
0
0.1
10
100
1
OUTPUT CURRENT (mA)
–1.0
1000
0
100
200
400
300
LOAD CURRENT (mA)
3419 G13
500
600
–1.0
0.4
0.2
0
100
300
200
400
LOAD CURRENT (mA)
500
600
3419 G15
Start-Up from Shutdown
VOUT = 1.8V
ILOAD = 100mA
Burst Mode OPERATION
PULSE SKIP MODE
3419 G14
Line Regulation
0.6
40
3419 G11
100
90
50
20
VIN = 2.7V
VIN = 3.6V
VIN = 4.2V
10
1000
60
30
3419 G10
VOUT ERROR (%)
TA = 25°C, VIN = 3.6V, unless otherwise noted.
Start-Up from Shutdown
RUN
2V/DIV
RUN
2V/DIV
VOUT
1V/DIV
VOUT
1V/DIV
IL
500mA/DIV
ILOAD
500mA/DIV
0
–0.2
–0.4
–0.6
2.5
250μs/DIV
3.0
3.5
4.0
VIN (V)
4.5
5.0
5.5
VIN = 3.6V
VOUT = 1.8V
ILOAD = 0A
3419 G17
250μs/DIV
3419 G18
VIN = 3.6V
VOUT = 1.8V
RLOAD = 3Ω
3419 G16
3419f
5
LTC3419
TYPICAL PERFORMANCE CHARACTERISTICS
Load Step
TA = 25°C, VIN = 3.6V, unless otherwise noted.
Load Step
Load Step
VOUT
100mV/DIV
AC-COUPLED
VOUT
100mV/DIV
AC-COUPLED
VOUT
100mV/DIV
AC-COUPLED
IL
500mA/DIV
IL
500mA/DIV
IL
500mA/DIV
ILOAD
500mA/DIV
ILOAD
500mA/DIV
ILOAD
500mA/DIV
20μs/DIV
3419 G19
VIN = 3.6V
VOUT = 1.8V
ILOAD = 0A TO 600mA
PIN FUNCTIONS
20μs/DIV
VIN = 3.6V
VOUT = 1.8V
ILOAD = 40mA TO 600mA
3419 G20
20μs/DIV
3419 G21
VIN = 3.6V
VOUT = 1.2V
ILOAD = 40mA TO 600mA
(DD/MS)
VFB1 (Pin 1/Pin 1): Regulator 1 Output Feedback. Receives
the feedback voltage from the external resistive divider
across the regulator 1 output. Nominal voltage for this
pin is 0.6V.
RUN1 (Pin 2/Pin 2): Regulator 1 Enable. Forcing this pin
to VIN enables regulator 1, while forcing it to GND causes
regulator 1 to shut down.
MODE (Pin 3/Pin 3): Mode Select Input. To select pulseskipping mode, tie to VIN. Grounding this pin selects Burst
Mode operation. Do not leave this pin floating.
SW1 (Pin 4/Pin 4): Regulator 1 Switch Node Connection
to the Inductor. This pin swings from VIN to GND.
VIN (Pin 5/Pin 7): Main Power Supply. Must be closely
de-coupled to GND.
SW2 (Pin 6/Pin 8): Regulator 2 Switch Node Connection
to the Inductor. This pin swings from VIN to GND.
RUN2 (Pin 7/Pin 9): Regulator 2 Enable. Forcing this pin
to VIN enables regulator 2, while forcing it to GND causes
regulator 2 to shut down.
VFB2 (Pin 8/Pin 10): Regulator 2 Output Feedback. Receives the feedback voltage from the external resistive
divider across the regulator 2 output. Nominal voltage
for this pin is 0.6V.
Exposed Pad (Pin 9/NA): Ground. The Exposed Pad must
be soldered to PCB for optimal thermal performance.
GND (NA/Pins 5, 6): Ground. Connect to the (–) terminal
of COUT, and the (–) terminal of CIN. Pin 5 of the MS package must be soldered to the PC board for optimal thermal
performance.
3419f
6
LTC3419
FUNCTIONAL DIAGRAM
REGULATOR 1
MODE
3
BURST
CLAMP
5 VIN
SLOPE
COMP
VFB1
–
–
1
EA
0.6V
VSLEEP
+
–
SLEEP
ITH
+
ICOMP
+
BURST
S
Q
RS
LATCH
R
Q
SOFT-START
SWITCHING
LOGIC
AND
BLANKING
CIRCUIT
ANTI
SHOOTTHRU
4 SW1
+
IRCMP
–
SHUTDOWN
RUN1
2
SLEEP2
0.6V REF
RUN2
9 GND
SLEEP1
OSC
7
OSC
VFB2
8
REGULATOR 2 (IDENTICAL TO REGULATOR 1)
6 SW2
3419 FD
3419f
7
LTC3419
OPERATION
The LTC3419 uses a constant-frequency, current mode
architecture. The operating frequency is set at 2.25MHz.
Both channels share the same clock and run in-phase.
The output voltage is set by an external resistor divider
returned to the VFB pins. An error amplifier compares the
divided output voltage with a reference voltage of 0.6V and
regulates the peak inductor current accordingly.
Main Control Loop
During normal operation, the top power switch (P-channel
MOSFET) is turned on at the beginning of a clock cycle
when the VFB voltage is below the reference voltage. The
current into the inductor and the load increases until the
peak inductor current (controlled by ITH) is reached. The
RS latch turns off the synchronous switch and energy
stored in the inductor is discharged through the bottom
switch (N-channel MOSFET) into the load until the next
clock cycle begins, or until the inductor current begins to
reverse (sensed by the IRCMP comparator).
MOSFET on. This cycle repeats at a rate that is dependent
on load demand.
For applications where low ripple voltage and constantfrequency operation is a higher priority than light load
efficiency, pulse-skipping mode can be used by connecting the MODE pin to VIN. In this mode, the peak inductor
current is not fixed, which allows the LTC3419 to switch
at a constant-frequency down to very low currents, where
it will begin skipping pulses.
Dropout Operation
When the input supply voltage decreases toward the
output voltage the duty cycle increases to 100%, which
is the dropout condition. In dropout, the PMOS switch is
turned on continuously with the output voltage being equal
to the input voltage minus the voltage drops across the
internal P-channel MOSFET and the inductor.
The peak inductor current is controlled by the internally
compensated ITH voltage, which is the output of the error amplifier. This amplifier regulates the VFB pin to the
internal 0.6V reference by adjusting the peak inductor
current accordingly.
An important design consideration is that the RDS(ON)
of the P-channel switch increases with decreasing input
supply voltage (see Typical Performance Characteristics).
Therefore, the user should calculate the worst-case power
dissipation when the LTC3419 is used at 100% duty cycle
with low input voltage (see Thermal Considerations in the
Applications Information section).
Light Load Operation
Soft-Start
There are two modes to control the LTC3419 at light load
currents: Burst Mode operation and pulse-skipping mode.
Both automatically transition from continuous operation
to the selected mode when the load current is low.
In order to minimize the inrush current on the input bypass
capacitor, the LTC3419 slowly ramps up the output voltage
during start-up. Whenever the RUN1 or RUN2 pin is pulled
high, the corresponding output will ramp from zero to
full-scale over a time period of approximately 750μs. This
prevents the LTC3419 from having to quickly charge the
output capacitor and thus supplying an excessive amount
of instantaneous current.
To optimize efficiency, Burst Mode operation can be selected
by grounding the MODE pin. When the load is relatively
light, the peak inductor current (as set by ITH) remains
fixed at approximately 60mA and the PMOS switch operates
intermittently based on load demand. By running cycles
periodically, the switching losses are minimized.
The duration of each burst event can range from a few
cycles at light load to almost continuous cycling with
short sleep intervals at moderate loads. During the sleep
intervals, the load current is being supplied solely from
the output capacitor. As the output voltage droops, the
error amplifier output rises above the sleep threshold,
signaling the burst comparator to trip and turn the top
Short-Circuit Protection
When either regulator output is shorted to ground, the
corresponding internal N-channel switch is forced on for
a longer time period for each cycle in order to allow the
inductor to discharge, thus preventing inductor current
runaway. This technique has the effect of decreasing
switching frequency. Once the short is removed, normal
operation resumes and the regulator output will return to
its nominal voltage.
3419f
8
LTC3419
APPLICATIONS INFORMATION
A general LTC3419 application circuit is shown in Figure 1.
External component selection is driven by the load requirement, and begins with the selection of the inductor L. Once
the inductor is chosen, CIN and COUT can be selected.
Inductor Selection
Although the inductor does not influence the operating frequency, the inductor value has a direct effect on
ripple current. The inductor ripple current ΔIL decreases
with higher inductance and increases with higher VIN or
VOUT :
V
Δ IL = OUT
fO • L
⎛
⎞
V
• ⎜ 1 − OUT ⎟
VIN ⎠
⎝
(1)
Accepting larger values of ΔIL allows the use of low
inductances, but results in higher output voltage ripple,
greater core losses, and lower output current capability.
A reasonable starting point for setting ripple current is
40% of the maximum output load current. So, for a 600mA
regulator, ΔIL = 240mA (40% of 600mA).
The inductor value will also have an effect on Burst Mode
operation. The transition to low current operation begins
when the peak inductor current falls below a level set by
the internal burst clamp. Lower inductor values result in
higher ripple current which causes the transition to occur
at lower load currents. This causes a dip in efficiency in
the upper range of low current operation. Furthermore,
lower inductance values will cause the bursts to occur
with increased frequency.
Inductor Core Selection
Different core materials and shapes will change the size/current and price/current relationship of an inductor. Toroid
VIN
2.5V TO 5.5V
C1
LTC3419
SW2
CF1
VFB2
R4
R3
GND
MANUFACTURER
Taiyo Yuden
PART NUMBER
CB2016T2R2M
CB2012T2R2M
CB2016T3R3M
MAX DC
VALUE CURRENT
2.2μH
2.2μH
3.3μH
510mA
530mA
410mA
DCR
HEIGHT
0.13Ω 1.6mm
0.33Ω 1.25mm
0.27Ω 1.6mm
Panasonic
ELT5KT4R7M
4.7μH
950mA
0.2Ω
1.2mm
Sumida
CDRH2D18/LD
4.7μH
630mA
0.086Ω
2mm
Murata
LQH32CN4R7M23
4.7μH
450mA
0.2Ω
2mm
Taiyo Yuden
NR30102R2M
NR30104R7M
2.2μH
4.7μH
1100mA
750mA
0.1Ω
0.19Ω
1mm
1mm
FDK
FDKMIPF2520D
FDKMIPF2520D
FDKMIPF2520D
4.7μH
3.3μH
2.2μH
1100mA
1200mA
1300mA
0.11Ω
0.1Ω
0.08Ω
1mm
1mm
1mm
TDK
VLF3010AT4R7MR70
VLF3010AT3R3MR87
VLF3010AT2R2M1R0
4.7μH
700mA
0.28Ω
1mm
3.3μH
870mA
0.17Ω
1mm
2.2μH
1000mA
0.12Ω
1mm
Input Capacitor (CIN) Selection
In continuous mode, the input current of the converter is a
square wave with a duty cycle of approximately VOUT / VIN .
To prevent large voltage transients, a low equivalent series
resistance (ESR) input capacitor sized for the maximum
RMS current must be used. The maximum RMS capacitor
current is given by:
VOUT ( VIN − VOUT )
VIN
L1
SW1
CF2
COUT2
Table 1. Representative Surface Mount Inductors
IRMS ≈ IMAX
RUN2 VIN RUN1
MODE
L2
VOUT2
or shielded pot cores in ferrite or permalloy materials are
small and do not 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 versus size
requirements, and any radiated field/EMI requirements,
than on what the LTC3419 requires to operate. Table 1
shows some typical surface mount inductors that work
well in LTC3419 applications.
VOUT1
VFB1
R1
R2
COUT1
3419 F01
Where the maximum average output current IMAX equals
the peak current minus half the peak-to-peak ripple current, IMAX = ILIM – ΔIL /2. This formula has a maximum at
VIN = 2VOUT, where IRMS = IOUT/2. This simple worst-case
is commonly used to design because even significant
Figure 1. LTC3419 General Schematic
3419f
9
LTC3419
APPLICATIONS INFORMATION
deviations do not offer much relief. Note that capacitor
manufacturer’s ripple current ratings are often based on
only 2000 hours lifetime. This makes it advisable to further
derate the capacitor, or choose a capacitor rated at a higher
temperature than required. Several capacitors may also be
paralleled to meet the size or height requirements of the
design. An additional 0.1μF to 1μF ceramic capacitor is
also recommended on VIN for high frequency decoupling
when not using an all-ceramic capacitor solution.
However, care must be taken when ceramic capacitors are
used at the input. When a ceramic capacitor is used at the
input and the power is supplied by a wall adapter through
long wires, a load step at the output can induce ringing at
the input, 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. For more information, see Application Note 88.
Output Capacitor (COUT) Selection
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.
The selection of COUT is driven by the required effective
series resistance (ESR). Typically, once the ESR requirement for COUT has been met, the RMS current rating
generally far exceeds the IRIPPLE(P-P) requirement. The
output ripple ΔVOUT is determined by:
⎛
1 ⎞
Δ VOUT ≈ Δ IL ⎜ ESR +
8 fOCOUT ⎟⎠
⎝
where fO = operating frequency, COUT = output capacitance
and ΔIL = ripple current in the inductor. For a fixed output
voltage, the output ripple is highest at maximum input
voltage since ΔIL increases with input voltage.
If tantalum capacitors are used, 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
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 LTC3419 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.
Setting the Output Voltage
The LTC3419 regulates the VFB1 and VFB2 pins to 0.6V
during regulation. Thus, the output voltage is set by a
resistive divider according to the following formula:
⎛ R2 ⎞
VOUT = 0 . 6 V ⎜ 1 + ⎟
⎝
R1⎠
(2)
Keeping the current small (< 10μA) in these resistors
maximizes efficiency, but making it too small may allow
stray capacitance to cause noise problems or reduce the
phase margin of the error amp loop.
To improve the frequency response of the main control
loop, a feedback capacitor (CF) may also be used. Great
care should be taken to route the VFB line away from noise
sources, such as the inductor or the SW line.
Fixed output versions of the LTC3419 (e.g. LTC3419-1)
include an internal resistive divider, eliminating the need
for external resistors. The resistor divider is chosen such
that the VFB input current is approximately 3μA. For these
versions the VFB pin should be connected directly to VOUT.
Table 2 lists the fixed output voltages available for the
LTC3419.
Table 2. Fixed Output Voltage Versions
PART NUMBER
LTC3419
LTC3419-1
VOUT1
VOUT2
Adjustable
Adjustable
1.575V
1.8V
3419f
10
LTC3419
APPLICATIONS INFORMATION
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, VOUT immediately shifts by an amount
equal to ΔILOAD • ESR, where ESR is the effective series
resistance of COUT. ΔILOAD also begins to charge or discharge COUT generating a feedback error signal used by the
regulator to return VOUT to its steady-state value. During
this recovery time, VOUT can be monitored for overshoot
or ringing that would indicate a stability problem.
The initial output voltage step may not be within the
bandwidth of the feedback loop, so the standard second
order overshoot/DC ratio cannot be used to determine the
phase margin. In addition, feedback capacitors (CF1 and
CF2) can be added to improve the high frequency response,
as shown in Figure 1. Capacitor CF provides phase lead by
creating a high frequency zero with R2 which improves
the phase margin.
The output voltage settling behavior is related to the stability
of the closed-loop system and will demonstrate the actual
overall supply performance. For a detailed explanation of
optimizing the compensation components, including a review of control loop theory, refer to Application Note 76.
In some applications, a more severe transient can be caused
by switching in loads with large (>1μF) input capacitors.
The discharged input capacitors are effectively put in parallel with COUT , causing a rapid drop in VOUT. No regulator
can deliver enough current to prevent this problem if the
switch connecting the load has low resistance and is driven
quickly. The solution is to limit the turn-on speed of the
load switch driver. A Hot Swap™ controller is designed
specifically for this purpose and usually incorporates current limiting, short-circuit protection, and soft-starting.
Efficiency Considerations
The percent 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. Percent efficiency can
be expressed as:
% Efficiency = 100% – (L1 + L2 + L3 + ...)
where L1, L2, etc., are the individual losses as a percentage of input power.
Although all dissipative elements in the circuit produce
losses, four sources usually account for the losses in
LTC3419 circuits: 1) VIN quiescent current, 2) switching
losses, 3) I2R losses, 4) other system losses.
1. The VIN current is the DC supply current given in the
Electrical Characteristics which excludes MOSFET
driver and control currents. VIN current results in a
small (<0.1%) loss that increases with VIN, even at
no load.
2. The switching current is the sum of the MOSFET driver
and control currents. The MOSFET driver current results from switching the gate capacitance of the power
MOSFETs. Each time a MOSFET gate is switched from
low to high to low again, a packet of charge dQ moves
from VIN to ground. The resulting dQ/dt is a current out
of VIN that is typically much larger than the DC bias current. In continuous mode, IGATECHG = fO(QT + QB), where
QT and QB are the gate charges of the internal top and
bottom MOSFET switches. The gate charge losses are
proportional to VIN and thus their effects will be more
pronounced at higher supply voltages.
3. I2R losses are calculated from the DC resistances
of the internal switches, RSW , and external inductor,
RL. In continuous mode, the average output current
flows through inductor L, but is “chopped” between
the internal top and bottom switches. 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)
Hot Swap is a trademark of Linear Technology Corporation.
3419f
11
LTC3419
APPLICATIONS INFORMATION
The RDS(ON) for both the top and bottom MOSFETs can be
obtained from the Typical Performance Characteristics
curves. Thus, to obtain I2R losses:
I2R losses = IOUT2 • (RSW + RL)
4. Other “hidden” losses, such as copper trace and internal
battery resistances, can account for additional efficiency
degradations in portable systems. It is very important
to include these “system” level losses in the design of a
system. The internal battery and fuse resistance losses
can be minimized by making sure that CIN has adequate
charge storage and very low ESR at the switching frequency. Other losses, including diode conduction losses
during dead-time, and inductor core losses, generally
account for less than 2% total additional loss.
Thermal Considerations
In a majority of applications, the LTC3419 does not dissipate much heat due to its high efficiency. In the unlikely
event that the junction temperature somehow reaches approximately 150°C, both power switches will be turned off
and the SW node will become high impedance. The goal
of the following thermal analysis is to determine whether
the power dissipated causes enough temperature rise to
exceed the maximum junction temperature (125°C) of the
part. The temperature rise is given by:
TRISE = 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. The junction temperature,
TJ, is given by:
TJ = TRISE + TAMBIENT
As a worst-case example, consider the case when the
LTC3419 is in dropout on both channels at an input voltage of 2.7V with a load current of 600mA and an ambient temperature of 70°C. From the Typical Performance
Characteristics graph of Switch Resistance, the RDS(ON)
of the main switch is 0.6Ω. Therefore, power dissipated
by each channel is:
PD = IOUT2 • RDS(ON) = 216mV
Given that the thermal resistance of a properly soldered
DFN package is approximately 40°C/W, the junction
temperature of an LTC3419 device operating in a 70°C
ambient temperature is approximately:
TJ = (2 • 0.216W • 40°C/W) + 70°C = 87.3°C
which is well below the absolute maximum junction temperature of 125°C.
PC Board Layout Considerations
When laying out the printed circuit board, the following
checklist should be used to ensure proper operation of
the LTC3419. These items are also illustrated graphically
in the layout diagrams of Figures 2 and 3. Check the following in your layout:
1. Does the capacitor CIN connect to the power VIN (Pin 5)
and GND (Pin 9) as closely as possible? This capacitor
provides the AC current of the internal power MOSFETs
and their drivers.
2. Are the respective COUT and L closely connected? The
(–) plate of COUT returns current to GND and the (–)
plate of CIN.
3. The resistor divider, R1 and R2, must be connected
between the (+) plate of COUT1 and a ground sense line
terminated near GND (Pin 9). The feedback signals VFB1
and VFB2 should be routed away from noisy components
and traces, such as the SW lines (Pins 4 and 6), and
their trace length should be minimized.
4. Keep sensitive components away from the SW pins, if
possible. The input capacitor CIN and the resistors R1,
R2, R3 and R4 should be routed away from the SW
traces and the inductors.
5. A ground plane is preferred, but if not available, keep
the signal and power grounds segregated with small
signal components returning to the GND pin at a single
point. These ground traces should not share the high
current path of CIN or COUT.
6. Flood all unused areas on all layers with copper.
Flooding with copper will reduce the temperature rise
of power components. These copper areas should be
connected to VIN or GND.
3419f
12
LTC3419
APPLICATIONS INFORMATION
VIN
2.5V TO 5.5V
C1
RUN2 VIN RUN1
MODE
LTC3419
L2
VOUT2
SW2
L1
VOUT1
SW1
CF2
CF1
VFB2
R4
COUT2
R3
GND
VFB1
R2
R1
COUT1
3419 F02
BOLD LINES INDICATE HIGH CURRENT PATHS
Figure 2. LTC3419 Layout Diagram (See Board Layout Checklist)
CF1
CF2
R2
R1
R3
R4
VOUT1
VOUT2
COUT1
COUT2
VIA TO VIN
L1
VFB1
VFB2
RUN1
RUN2
MODE
SW2
SW1
L2
VIN
VIA TO GND
GND
CIN
3419 F03
Figure 3. LTC3419 Suggested Layout
Design Example
As a design example, consider using the LTC3419 in a
portable application with a Li-Ion battery. The battery
provides a VIN ranging from 2.8V to 4.2V. The load on
each channel requires a maximum of 600mA in active
mode and 2mA in standby mode. The output voltages are
VOUT1 = 2.5V and VOUT2 = 1.8V.
Start with channel 1. First, calculate the inductor value
for about 40% ripple current (240mA in this example) at
maximum VIN. Using a derivation of Equation 1:
L1 =
2 . 5V
⎛ 2 . 5V ⎞
• ⎜ 1−
= 1 . 8 7μH
2 . 25MHz • (240mA) ⎝
4 . 2V ⎟⎠
For the inductor, use the closest standard value of
2.2μH.
A 10μF ceramic capacitor should be more than sufficient
for this output capacitor. As for the input capacitor, a
typical value of CIN = 10μF should suffice, as the source
impedance of a Li-Ion battery is very low.
The feedback resistors program the output voltage. To
maintain high efficiency at light loads, the current in these
resistors should be kept small. Choosing 10μA with the
0.6V feedback voltage makes R1~60k. A close standard
1% resistor is 59k. Using Equation 2.
⎛V
⎞
R2 = ⎜ OUT − 1⎟ • R1 = 187k
⎝ 0.6
⎠
An optional 22pF feedback capacitor (CF1) may be used
to improve transient response.
3419f
13
LTC3419
APPLICATIONS INFORMATION
Using the same analysis for channel 2 (VOUT2 = 1.8V),
the results are:
100
90
80
L2 = 1.9μH
EFFICIENCY (%)
70
R3 = 59k
R4 = 118k
60
50
40
30
20
CF2 = 22pF
VIN = 2.7V
VIN = 3.6V
VIN = 4.2V
10
VOUT = 1.8V
0
0.1
1
10
100
OUTPUT CURRENT (mA)
Figure 4 shows the complete schematic for this example,
along with the efficiency curve and transient response.
1000
100
VIN
2.5V TO 5.5V
80
RUN2 VIN RUN1
MODE
L2
2.2μH
SW2
70
L1
2.2μH
LTC3419
VOUT1
2.5V AT
600mA
SW1
CF2, 22pF
EFFICIENCY (%)
VOUT2
1.8V AT
600mA
90
C1
10μF
CF1, 22pF
60
50
40
30
COUT2
10μF
VFB2
R4
118k
R3
59k
VFB1
GND
R1
59k
20
COUT1
10μF
R2
187k
10
VOUT = 2.5V
0
0.1
3419 F04a
C1, C2, C3: TAIYO YUDEN JMK316BJ106ML
L1, L2: TDK VLF3010AT2R2M1RD
1
10
100
OUTPUT CURRENT (mA)
1000
3419 F04b
Figure 4a. Design Example Circuit
Figure 4b. Efficiency vs Output Current
Load Step
Transient Response
VOUT
100mV/DIV
AC-COUPLED
VOUT
100mV/DIV
AC-COUPLED
IL
500mA/DIV
IL
500mA/DIV
ILOAD
500mA/DIV
ILOAD
500mA/DIV
20μs/DIV
VIN = 3.6V
VOUT = 1.8V
ILOAD = 40mA TO 600mA
VIN = 2.7V
VIN = 3.6V
VIN = 4.2V
3419 F04c1
20μs/DIV
VIN = 3.6V
VOUT = 2.5V
ILOAD = 40mA TO 600mA
3419 F04c2
Figure 4c. Transient Response
3419f
14
LTC3419
PACKAGE DESCRIPTION
DD Package
8-Lead Plastic DFN (3mm × 3mm)
(Reference LTC DWG # 05-08-1698)
R = 0.115
TYP
5
0.38 ± 0.10
8
0.675 ±0.05
3.5 ±0.05
1.65 ±0.05
2.15 ±0.05 (2 SIDES)
3.00 ±0.10
(4 SIDES)
PACKAGE
OUTLINE
1.65 ± 0.10
(2 SIDES)
PIN 1
TOP MARK
(NOTE 6)
0.25 ± 0.05
(DD) DFN 1203
4
0.25 ± 0.05
0.75 ±0.05
0.200 REF
0.50
BSC
2.38 ±0.05
(2 SIDES)
1
0.50 BSC
2.38 ±0.10
(2 SIDES)
0.00 – 0.05
BOTTOM VIEW—EXPOSED PAD
RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS
NOTE:
1. DRAWING TO BE MADE A JEDEC PACKAGE OUTLINE M0-229 VARIATION OF (WEED-1)
2. DRAWING NOT TO SCALE
3. ALL DIMENSIONS ARE IN MILLIMETERS
4. DIMENSIONS OF EXPOSED PAD ON BOTTOM OF PACKAGE DO NOT INCLUDE
MOLD FLASH. MOLD FLASH, IF PRESENT, SHALL NOT EXCEED 0.15mm ON ANY SIDE
5. EXPOSED PAD SHALL BE SOLDER PLATED
6. SHADED AREA IS ONLY A REFERENCE FOR PIN 1 LOCATION
ON TOP AND BOTTOM OF PACKAGE
MS Package
10-Lead Plastic MSOP
(Reference LTC DWG # 05-08-1661)
3.00 ± 0.102
(.118 ± .004)
(NOTE 3)
0.889 ± 0.127
(.035 ± .005)
10 9 8 7 6
5.23
(.206)
MIN
3.20 – 3.45
(.126 – .136)
0.254
(.010)
1 2 3 4 5
0° – 6° TYP
0.86
(.034)
REF
1.10
(.043)
MAX
DETAIL “A”
DETAIL “A”
3.00 ± 0.102
(.118 ± .004)
(NOTE 4)
4.90 ± 0.152
(.193 ± .006)
0.50
0.305 ± 0.038
(.0197)
(.0120 ± .0015)
BSC
TYP
RECOMMENDED SOLDER PAD LAYOUT
0.497 ± 0.076
(.0196 ± .003)
REF
0.18
(.007)
SEATING
PLANE
GAUGE PLANE
0.53 ± 0.152
(.021 ± .006)
NOTE:
1. DIMENSIONS IN MILLIMETER/(INCH)
2. DRAWING NOT TO SCALE
3. DIMENSION DOES NOT INCLUDE MOLD FLASH, PROTRUSIONS OR GATE BURRS. MOLD
FLASH, PROTRUSIONS OR GATE BURRS SHALL NOT EXCEED 0.152mm (.006") PER SIDE
0.17 – 0.27
(.007 – .011)
TYP
0.50
(.0197)
BSC
0.127 ± 0.076
(.005 ± .003)
MSOP (MS) 0603
4. DIMENSION DOES NOT INCLUDE INTERLEAD FLASH OR PROTRUSIONS.
INTERLEAD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.152mm (.006") PER SIDE
5. LEAD COPLANARITY (BOTTOM OF LEADS AFTER FORMING) SHALL BE
0.102mm (.004") MAX
3419f
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.
15
LTC3419
TYPICAL APPLICATION
Dual 600mA Buck Converter
VIN
2.5V TO 5.5V
VIN
2.5V TO 5.5V
C1
10μF
L1
3.3μH
LTC3419
SW2
CF1, 22pF
VFB2
R4
118k
VOUT1
2.5V AT
600mA
SW1
CF2, 22pF
COUT2
10μF
C1
10μF
RUN2 VIN RUN1
MODE
L2
3.3μH
VOUT2
1.8V AT
600mA
1.8V/1.575V Dual 600mA Buck Converter
R3
59k
GND
VFB1
R1
59k
COUT1
10μF
R2
187k
L2
3.3μH
VOUT2
1.8V AT
600mA
RUN2 VIN RUN1
MODE
SW2
COUT2
10μF
L1
3.3μH
LTC3419-1
VFB2
SW1
GND
VFB1
COUT1
10μF
3419 TA02
C1, C2, C3: TAIYO YUDEN JMK316BJ106ML
L1, L2: TDK VLF3010AT3R3M1RD
VOUT1
1.575V AT
600mA
3419 TA03
C1, C2, C3: TAIYO YUDEN JMK316BJ106ML
L1, L2: TDK VLF3010AT3R3M1RD
RELATED PARTS
PART NUMBER
DESCRIPTION
COMMENTS
LTC3405/LTC3405A
300mA IOUT, 1.5MHz, Synchronous
Step-Down DC/DC Converters
95% Efficiency, VIN(MIN) = 2.5V, VIN(MAX) = 5.5V, VOUT(MIN) = 0.8V, IQ = 20μA, ISD = <1μA,
ThinSOTTM Package
LTC3406/LTC3406B
600mA IOUT, 1.5MHz, Synchronous
Step-Down DC/DC Converters
96% Efficiency, VIN(MIN) = 2.5V, VIN(MAX) = 5.5V, VOUT(MIN) = 0.6V, IQ = 20μA, ISD = <1μA,
ThinSOT Package
LTC3407/LTC3407-2
Dual 600mA/800mA IOUT, 1.5MHz/
2.25MHz, Synchronous Step-Down
DC/DC Converters
95% Efficiency, VIN(MIN) = 2.5V, VIN(MAX) = 5.5V, VOUT(MIN) = 0.6V, IQ = 40μA, ISD = <1μA,
MS10E and DFN Packages
LTC3409
600mA IOUT, 1.7MHz/2.6MHz,
Synchronous Step-Down DC/DC
Converter
96% Efficiency, VIN(MIN) = 1.6V, VIN(MAX) = 5.5V, VOUT(MIN) = 0.6V, IQ = 65μA, ISD = <1μA,
DFN Package
LTC3410/LTC3410B
300mA IOUT, 2.25MHz, Synchronous
Step-Down DC/DC Converters
95% Efficiency, VIN(MIN) = 2.5V, VIN(MAX) = 5.5V, VOUT(MIN) = 0.8V, IQ = 26μA, ISD = <1μA,
SC70 Package
LTC3411
1.25A IOUT, 4MHz, Synchronous
Step-Down DC/DC Converter
95% Efficiency, VIN(MIN) = 2.5V, VIN(MAX) = 5.5V, VOUT(MIN) = 0.8V, IQ = 60μA, ISD = <1μA,
MS10 and DFN Packages
LTC3412
2.5A IOUT 4MHz, Synchronous
Step-Down DC/DC Converter
95% Efficiency, VIN(MIN) = 2.5V, VIN(MAX) = 5.5V, VOUT(MIN) = 0.8V, IQ = 60μA, ISD = <1μA,
TSSOP-16E Package
LTC3441/LTC3442,
LTC3443
1.2A IOUT 2MHz, Synchronous
Buck-Boost DC/DC Converters
95% Efficiency, VIN(MIN) = 2.4V, VIN(MAX) = 5.5V, VOUT(MIN): 2.4V to 5.25V, IQ = 50μA,
ISD = <1μA, DFN Package
LTC3531/LTC3531-3/ 200mA IOUT, 1.5MHz, Synchronous
Buck-Boost DC/DC Converter
LTC3531-3.3
95% Efficiency, VIN(MIN) = 1.8V, VIN(MAX) = 5.5V, VOUT(MIN): 2V to 5V, IQ = 16μA,
ISD = <1μA, ThinSOT and DFN Packages
LTC3532
500mA IOUT, 2MHz, Synchronous
Buck-Boost DC/DC Converter
95% Efficiency, VIN(MIN) = 2.4V, VIN(MAX) = 5.5V, VOUT(MIN): 2.4V to 5.25V, IQ = 35μA,
ISD = <1μA, MS10 and DFN Packages
LTC3547/LTC3547B
Dual 300mA IOUT, 2.25MHz,
Synchronous Step-Down DC/DC
Converters
95% Efficiency, VIN(MIN) = 2.5V, VIN(MAX) = 5.5V, VOUT(MIN): 0.6V, IQ = 40μA, ISD = <1μA,
DFN-8 Package
LTC3548/LTC3548-1/ Dual 400mA and 800mA IOUT,
LTC3548-2
2.25MHz, Synchronous Step-Down
DC/DC Converters
95% Efficiency, VIN(MIN) = 2.5V, VIN(MAX) = 5.5V, VOUT(MIN): 0.6V, IQ = 40μA, ISD = <1μA,
MS10E and DFN Packages
LTC3561
95% Efficiency, VIN(MIN) = 2.5V, VIN(MAX) = 5.5V, VOUT(MIN): 0.8V, IQ = 240μA, ISD = <1μA,
DFN Package
1.25A IOUT, 4MHz, Synchronous
Step-Down DC/DC Converter
ThinSOT™ is a trademark of Linear Technology Corporation.
3419f
16 Linear Technology Corporation
LT 0407 • PRINTED IN USA
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 ● FAX: (408) 434-0507
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www.linear.com
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