FEATURES
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LTC3407
Dual Synchronous, 600mA,
1.5MHz Step-Down
DC/DC Regulator
DESCRIPTION
The LTC
®
3407 is a dual, constant frequency, synchronous
step down DC/DC converter. Intended for low power ap-
plications, it operates from 2.5V to 5.5V input voltage
range and has a constant 1.5MHz switching frequency,
allowing the use of tiny, low cost capacitors and inductors
2mm or less in height. Each output voltage is adjustable
from 0.6V to 5V. Internal synchronous 0.35Ω, 1A power
switches provide high efficiency without the need for
external Schottky diodes.
A user selectable mode input is provided to allow the user
to trade-off ripple noise for low power efficiency. Burst
Mode
®
operation provides high efficiency at light loads,
while pulse-skipping mode provides low ripple noise at
light loads.
To further maximize battery life, the P-channel MOSFETs
are turned on continuously in dropout (100% duty cycle),
and both channels draw a total quiescent current of only
40μA. In shutdown, the device draws <1μA.
L,
LT, LTC, LTM, Burst Mode, Linear Technology and the Linear logo are registered trademarks
of Linear Technology Corporation. All other trademarks are the property of their respective
owners.
High Efficiency: Up to 96%
Very Low Quiescent Current: Only 40μA
1.5MHz Constant Frequency Operation
High Switch Current: 1A on Each Channel
No Schottky Diodes Required
Low R
DS(ON)
Internal Switches: 0.35Ω
Current Mode Operation for Excellent Line
and Load Transient Response
Short-Circuit Protected
Low Dropout Operation: 100% Duty Cycle
Ultralow Shutdown Current: I
Q
< 1μA
Output Voltages from 5V down to 0.6V
Power-On Reset Output
Externally Synchronizable Oscillator
Small Thermally Enhanced MSOP and 3mm
×
3mm
DFN Packages
APPLICATIONS
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PDAs/Palmtop PCs
Digital Cameras
Cellular Phones
Portable Media Players
PC Cards
Wireless and DSL Modems
TYPICAL APPLICATION
V
IN
= 2.5V
TO 5.5V
C1
10μF
RUN2
V
IN
RUN1
POR
L1
2.2μH
SW1
C4, 22pF
R5
100k
RESET
EFFICIENCY (%)
LTC3407 Efficiency Curve
100
95
90
85
80
75
70
R1
442k
R2
887k
C2
10μF
65
60
1
V
IN
= 3.3V
Burst Mode OPERATION
NO LOAD ON OTHER CHANNEL
10
100
LOAD CURRENT (mA)
1000
3407 TA02
2.5V
1.8V
MODE/SYNC
L2
2.2μH
SW2
C5, 22pF
LTC3407
V
OUT2
= 2.5V
AT 600mA
V
OUT1
= 1.8V
AT 600mA
C3
10μF
R4
887k
V
FB2
R3
280k
GND
V
FB1
C1, C2, C3: TAIYO YUDEN JMK316BJ106ML
L1, L2: MURATA LQH32CN2R2M33
3407 TA01
Figure 1. 2.5V/1.8V at 600mA Step-Down Regulators
3407fa
1
LTC3407
ABSOLUTE MAXIMUM RATINGS
(Note 1)
V
IN
Voltages .................................................– 0.3V to 6V
V
FB1
, V
FB2
Voltages .......................... –0.3V to V
IN
+ 0.3V
RUN1, RUN2 Voltages .................................–0.3V to V
IN
MODE/SYNC Voltage........................ –0.3V to V
IN
+ 0.3V
SW1, SW2 Voltage ........................... –0.3V to V
IN
+ 0.3V
POR
Voltage ................................................. –0.3V to 6V
Ambient Operating Temperature
Range (Note 2) .................................... –40°C to 85°C
Junction Temperature (Note 5) ............................. 125°C
Storage Temperature Range
LTC3407EMSE ...................................– 65°C to 150°C
LTC3407EDD ...................................... –65°C to 125°C
Lead Temperature (Soldering, 10 sec)
LTC3407EMSE only........................................... 300°C
PIN CONFIGURATION
TOP VIEW
V
FB1
RUN1
V
IN
SW1
GND
1
2
3
4
5
11
10 V
FB2
9 RUN2
8
POR
7 SW2
6 MODE/
SYNC
TOP VIEW
V
FB1
RUN1
V
IN
SW1
GND
1
2
3
4
5
10
9
8
7
6
V
FB2
RUN2
POR
SW2
MODE/
SYNC
11
DD PACKAGE
10-LEAD (3mm
×
3mm) PLASTIC DFN
T
JMAX
= 125°C,
θ
JA
= 45°C/W,
θ
JC
= 10°C/W
EXPOSED PAD IS PGND (PIN 11) MUST BE CONNECTED TO GND
MSE PACKAGE
10-LEAD PLASTIC MSOP
T
JMAX
= 125°C,
θ
JA
= 45°C/W,
θ
JC
= 10°C/W
EXPOSED PAD IS PGND (PIN 11) MUST BE CONNECTED TO GND
ORDER INFORMATION
LEAD FREE FINISH
LTC3407EDD#PBF
LTC3407EMSE#PBF
TAPE AND REEL
LTC3407EDD#TRPBF
LTC3407EMSE#TRPBF
PART MARKING
LAGK
LTABA
PACKAGE DESCRIPTION
10-Lead (3mm × 3mm) Plastic DFN
10-Lead (3mm × 3mm) Plastic MSOP
TEMPERATURE RANGE
–40°C to 85°C
–40°C to 85°C
Consult LTC Marketing for parts specified with wider operating temperature ranges.
Consult LTC Marketing for information on non-standard lead based finish parts.
For more information on lead free part marking, go to:
http://www.linear.com/leadfree/
For more information on tape and reel specifications, go to:
http://www.linear.com/tapeandreel/
The
l
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
IN
= 3.6V, unless otherwise specified. (Note 2)
SYMBOL
V
IN
I
FB
V
FB
ΔV
LINE REG
ΔV
LOAD REG
PARAMETER
Operating Voltage Range
Feedback Pin Input Current
Feedback Voltage (Note 3)
Reference Voltage Line Regulation
Output Voltage Load Regulation
0°C ≤ T
A
≤ 85°C
–40°C ≤ T
A
≤ 85°C
V
IN
= 2.5V to 5.5V (Note 3)
(Note 3)
CONDITIONS
●
●
●
ELECTRICAL CHARACTERISTICS
MIN
2.5
0.588
0.585
TYP
MAX
5.5
30
UNITS
V
nA
V
V
%/V
%
3407fa
0.6
0.6
0.3
0.5
0.612
0.612
0.5
2
LTC3407
ELECTRICAL CHARACTERISTICS
SYMBOL
I
S
PARAMETER
Input DC Supply Current
Active Mode
Sleep Mode
Shutdown
Oscillator Frequency
Synchronization Frequency
Peak Switch Current Limit
Top Switch On-Resistance
Bottom Switch On-Resistance
Switch Leakage Current
Power-On Reset Threshold
Power-On Reset On-Resistance
Power-On Reset Delay
V
RUN
I
RUN
V
MODE
RUN Threshold
RUN Leakage Current
Mode Threshold Low
Mode Threshold High
●
●
The
l
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
IN
= 3.6V, unless otherwise specified. (Note 2)
CONDITIONS
V
FB1
= V
FB2
= 0.5V
V
FB1
= V
FB2
= 0.63V, MODE/SYNC = 3.6V
RUN = 0V, V
IN
= 5.5V, MODE/SYNC = 0V
V
FBX
= 0.6V
V
IN
= 3V, V
FB
= 0.5V, Duty Cycle <35%
(Note 6)
(Note 6)
V
IN
= 5V, V
RUN
= 0V, V
FBX
= 0V
V
FBX
Ramping Up, MODE/SYNC = 0V
V
FBX
Ramping Down, MODE/SYNC = 0V
●
MIN
TYP
600
40
0.1
MAX
800
60
1
1.8
1.25
0.45
0.45
1
UNITS
μA
μA
μA
MHz
MHz
A
Ω
Ω
μA
%
%
f
OSC
f
SYNC
I
LIM
R
DS(ON)
I
SW(LKG)
POR
1.2
0.75
1.5
1.5
1
0.35
0.30
0.01
8.5
–8.5
100
262,144
200
1.5
1
0.5
V
IN
Ω
Cycles
V
μA
V
V
0.3
0
V
IN
– 0.5
1
0.01
Note 1:
Stresses beyond those listed under Absolute Maximum Ratings
may cause permanent damage to the device. Exposure to any Absolute
Maximum Rating condition for extended periods may affect device
reliability and lifetime.
Note 2:
The LTC3407E is guaranteed to meet specified performance
from 0°C to 70°C. Specifications over the – 40°C and 85°C operating
temperature range are assured by design, characterization and correlation
with statistical process controls.
Note 3:
The LTC3407 is tested in a proprietary test mode that connects V
FB
to the output of the error amplifier.
Note 4:
Dynamic supply current is higher due to the internal gate charge
being delivered at the switching frequency.
Note 5:
T
J
is calculated from the ambient T
A
and power dissipation P
D
according to the following formula: T
J
= T
A
+ (P
D
•
θ
JA
).
Note 6:
The DFN switch on-resistance is guaranteed by correlation to
wafer level measurements.
TYPICAL PERFORMANCE CHARACTERISTICS
Burst Mode Operation
SW
5V/DIV
SW
5V/DIV
Pulse-Skipping Mode
V
OUT
200mV/DIV
Load Step
V
OUT
100mV/DIV
I
L
200mA/DIV
V
OUT
10mV/DIV
I
L
200mA/DIV
3407 G01
I
L
500mA/DIV
I
LOAD
500mA/DIV
V
IN
= 3.6V
4μs/DIV
V
OUT
= 1.8V
I
LOAD
= 50mA
CIRCUIT OF FIGURE 1
V
IN
= 3.6V
1μs/DIV
V
OUT
= 1.8V
I
LOAD
= 50mA
CIRCUIT OF FIGURE 1
3407 G02
V
IN
= 3.6V
20μs/DIV
V
OUT
= 1.8V
I
LOAD
= 50mA TO 600mA
CIRCUIT OF FIGURE 1
3407 G03
3407fa
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LTC3407
TYPICAL PERFORMANCE CHARACTERISTICS
Efficiency vs Input Voltage
100
T
A
= 25°C
100mA
FREQUENCY (MHz)
1mA
85
80
75
70
65 V
OUT
= 1.8V
CIRCUIT OF FIGURE 1
60
4
5
2
3
INPUT VOLTAGE (V)
600mA
10mA
OSCILLATOR FREQUENCY (MHz)
95
90
EFFICIENCY (%)
1.65
1.60
1.55
1.50
1.45
1.40
1.35
6
3407 G04
Oscillator Frequency vs
Temperature
1.70
1.8
1.7
1.6
1.5
1.4
1.3
1.2
Oscillator Frequency vs Supply
Voltage
T
A
= 25°C
1.30
–50 –25
50
25
75
0
TEMPERATURE (°C)
100
125
2
3
4
SUPPLY VOLTAGE (V)
5
6
3407 G06
3407 G05
Reference Voltage vs
Temperature
0.615
0.610
REFERENCE VOLTAGE (V)
0.605
0.600
0.595
0.590
0.585
–50 –25
V
IN
= 3.6V
500
R
DS(ON)
vs Input Voltage
550
T
A
= 25°C
450
450
R
DS(ON)
(mΩ)
R
DS(ON)
(mΩ)
400
350
300
250
200
SYNCHRONOUS
SWITCH
MAIN
SWITCH
400
350
300
250
200
150
1
2
3
4
V
IN
(V)
5
6
7
3407 G08
R
DS(ON)
vs Temperature
V
IN
= 2.7V
V
IN
= 4.2V
V
IN
= 3.6V
500
50
25
75
0
TEMPERATURE (°C)
100
125
100
–50 –25
MAIN SWITCH
SYNCHRONOUS SWITCH
0
25 50 75 100 125 150
TEMPERATURE (°C)
3407 G09
3407 G07
Efficiency vs Load Current
100
2.7V
95
90
EFFICIENCY (%)
85
80
75
70
65
60
1
V
OUT
= 2.5V Burst Mode OPERATION
CIRCUIT OF FIGURE 1
10
100
LOAD CURRENT (mA)
1000
3407 G10
Efficiency vs Load Current
100
4
Burst Mode OPERATION
V
OUT
ERROR (%)
3
2
1
0
–1
–2
V
IN
= 3.6V, V
OUT
= 1.8V
NO LOAD ON OTHER CHANNEL
1
10
100
LOAD CURRENT (mA)
1000
3407 G11
Load Regulation
Burst Mode OPERATION
3.3V
4.2V
EFFICIENCY (%)
95
90
85
80
75
70
65
60
PULSE-SKIPPING
MODE
PULSE-SKIPPING
MODE
–3
–4
1
V
IN
= 3.6V, V
OUT
= 1.8V
NO LOAD ON OTHER CHANNEL
10
100
LOAD CURRENT (mA)
1000
3407 G12
3407fa
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LTC3407
TYPICAL PERFORMANCE CHARACTERISTICS
Efficiency vs Load Current
100
95
90
EFFICIENCY (%)
85
80
75
70
65
60
1
V
OUT
= 1.2V Burst Mode OPERATION
CIRCUIT OF FIGURE 1
10
100
LOAD CURRENT (mA)
1000
3407 G13
Efficiency vs Load Current
100
0.5
0.4
3.3V
90
EFFICIENCY (%)
4.2V
2.7V
V
OUT
ERROR (%)
0.3
0.2
0.1
0
–0.1
–0.2
–0.3
65
60
1
V
OUT
= 1.5V Burst Mode OPERATION
CIRCUIT OF FIGURE 1
10
100
LOAD CURRENT (mA)
1000
3407 G14
Line Regulation
V
OUT
= 1.8V
I
OUT
= 200mA
T
A
= 25°C
3.3V
4.2V
2.7V
95
85
80
75
70
–0.4
–0.5
2
3
4
V
IN
(V)
5
6
3407 G15
PIN FUNCTIONS
V
FB1
(Pin 1):
Output Feedback. Receives the feedback volt-
age from the external resistive divider across the output.
Nominal voltage for this pin is 0.6V.
RUN1 (Pin 2):
Regulator 1 Enable. Forcing this pin to V
IN
enables regulator 1, while forcing it to GND causes regulator
1 to shut down. This pin must be driven; do not float.
V
IN
(Pin 3):
Main Power Supply. Must be closely decoupled
to GND.
SW1 (Pin 4):
Regulator 1 Switch Node Connection to the
Inductor. This pin swings from V
IN
to GND.
GND (Pin 5):
Ground. This pin is not connected internally.
Connect to PCB ground for shielding.
MODE/SYNC (Pin 6):
Combination Mode Selection and
Oscillator Synchronization. This pin controls the opera-
tion of the device. When tied to V
IN
or GND, Burst Mode
operation or pulse-skipping mode is selected, respectively.
Do not float this pin. The oscillation frequency can be
synchronized to an external oscillator applied to this pin
and pulse-skipping mode is automatically selected.
SW2 (Pin 7):
Regulator 2 Switch Node Connection to the
Inductor. This pin swings from V
IN
to GND.
POR
(Pin 8):
Power-On Reset . This common-drain logic
output is pulled to GND when the output voltage is not
within ±8.5% of regulation and goes high after 175ms
when both channels are within regulation.
RUN2 (Pin 9):
Regulator 2 Enable. Forcing this pin to V
IN
enables regulator 2, while forcing it to GND causes regulator
2 to shut down. This pin must be driven; do not float.
V
FB2
(Pin 10):
Output Feedback. Receives the feedback
voltage from the external resistive divider across the output.
Nominal voltage for this pin is 0.6V.
Exposed Pad (GND) (Pin 11):
Power Ground. Connect to
the (–) terminal of C
OUT
, and (–) terminal of C
IN
. Must be
soldered to electrical ground on PCB.
3407fa
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