FEATURES
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LTC3407-3
Dual Synchronous,
1.8V/0.8A and 3.3V/0.8A
2.25MHz Step-Down DC/DC Regulator
DESCRIPTION
The LTC
®
3407-3 is a dual, constant frequency, synchro-
nous step down DC/DC converter. Intended for low power
applications, it operates from 3.3V to 5.5V input voltage
range and has a constant 2.25MHz switching frequency,
allowing the use of tiny, low cost capacitors and inductors
with a profile ≤1.0mm. Internal synchronous 0.35Ω, 1.2A
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 noise ripple for low power efficiency. Burst
Mode
®
operation provides high efficiency at light loads,
while pulse-skipping mode provides low noise ripple 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. Protected by U.S. Patents, including 5481178, 6580258, 6304066, 6127815, 6498466,
6611131.
Very Low Quiescent Current: Only 40μA
1.8V at 800mA/3.3V at 800mA
High Efficiency: Up to 95%
2.25MHz Constant Frequency Operation
High Switch Current: 1.2A on Each Channel
No Schottky Diodes Required
Low R
DS(ON)
Internal Switches: 0.35Ω
V
IN
: 3.3V to 5.5V
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
Power-On Reset Output
Externally Synchronizable Oscillator
Small Thermally Enhanced 3mm
×
3mm DFN Package
APPLICATIONS
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PDAs/Palmtop PCs
Digital Cameras
Cellular Phones
Portable Media Players
PC Cards
Wireless and DSL Modems
TYPICAL APPLICATION
LTC3407-3 Efficiency/Power Loss
100
V
IN
3.3V TO 5.5V
10μF
RUN2
V
IN
RUN1
POR
SW1
V
OUT1
GND
MODE/SYNC
V
OUT2
3.3V
2.2μH
SW2
10μF
V
OUT2
LTC3407-3
100k
EFFICIENCY (%)
RESET
2.2μH
V
OUT1
1.8V
10μF
34073 TA01
1
V
OUT
= 3.3V
V
OUT
= 1.8V
90
80
70
60
50
40
30
20
10
1
0.1
POWER LOSS (W)
V
OUT
= 3.3V
V
OUT
= 1.8V
0.01
0.001
V
IN
= 5V
Burst Mode OPERATION
NO LOAD ON OTHER CHANNEL
10
100
LOAD CURRENT (mA)
NOTE: IN DROPOUT, THE OUTPUT TRACKS THE INPUT VOLTAGE
Figure 1. 1.8V/3.3V at 800mA Step-Down Regulators
0.000
1000
34073 TA01b
34073fb
1
LTC3407-3
ABSOLUTE MAXIMUM RATINGS
(Note 1)
PIN CONFIGURATION
TOP VIEW
V
OUT1
RUN1
V
IN
SW1
GND
1
2
3
4
5
11
10 V
OUT2
9 RUN2
8
POR
7 SW2
6 MODE/
SYNC
V
IN
Voltages .................................................– 0.3V to 6V
V
OUT1
, V
OUT2
Voltages ..................... –0.3V to V
IN
+ 0.3V
RUN1, RUN2 Voltages .................................–0.3V to V
IN
MODE/SYNC Voltage....................................–0.3V to V
IN
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...................– 65°C to 125°C
DD PACKAGE
10-LEAD (3mm
×
3mm) PLASTIC DFN
T
JMAX
= 125°C,
θ
JA
= 40°C/W,
θ
JC
= 10°C/W
EXPOSED PAD (PIN 11) IS PGND, MUST BE SOLDERED TO PCB GND
ORDERING INFORMATION
LEAD FREE FINISH
LTC3407EDD-3#PBF
TAPE AND REEL
LTC3407EDD-3#TRPBF
PART MARKING
LCJB
PACKAGE DESCRIPTION
10-Lead (3mm × 3mm) Plastic DFN
TEMPERATURE RANGE
–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
V
OUT1
V
OUT2
ΔV
LINE REG
PARAMETER
Operating Voltage Range
Output Voltage (Note 3)
Output Voltage (Note 3)
0°C ≤ T
A
≤ 85°C
–40°C ≤ T
A
≤ 85°C
0°C ≤ T
A
≤ 85°C
–40°C ≤ T
A
≤ 85°C
CONDITIONS
●
●
●
ELECTRICAL CHARACTERISTICS
MIN
3.3
1.764
1.755
3.234
3.218
TYP
1.8
1.8
3.3
3.3
0.3
0.5
MAX
5.5
1.836
1.836
3.366
3.366
0.5
UNITS
V
V
V
V
V
%/V
%
Reference Voltage Line Regulation (Note 3) V
IN
= 3.3V to 5.5V (Channel 1)
V
IN
= 3.6V to 5.5V (Channel 2)
Input DC Supply Current (Note 4)
Active Mode
Sleep Mode
Shutdown
Oscillator Frequency
Synchronization Frequency
ΔV
LOAD REG
Output Voltage Load Regulation (Note 3)
I
S
V
OUT1
= 1.5V, V
OUT2
= 2.8V
V
OUT1
= 1.9V, V
OUT2
= 3.5V, MODE/SYNC = 3.6V
RUN = 0V, V
IN
= 5.5V, MODE/SYNC = 0V
V
OUT1
= 1.8V, V
OUT2
= 3.3V
●
700
40
0.1
1.8
2.25
2.25
950
60
1
2.7
μA
μA
μA
MHz
MHz
f
OSC
f
SYNC
34073fb
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LTC3407-3
ELECTRICAL CHARACTERISTICS
SYMBOL
I
LIM
R
DS(ON)
I
SW(LKG)
POR
PARAMETER
Peak Switch Current Limit, Channel 1 +
Channel 2
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
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. No pin shall exceed 6V.
Note 2:
The LTC3407E-3 is guaranteed to meet specified performance
from 0°C to 85°C. Specifications over the –40°C to 85°C operating
temperature range are assured by design, characterization and correlation
with statistical process controls.
●
●
The
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
IN
= 3V, V
OUT1
= 1.5V, V
OUT2
= 2.8V,
Duty Cycle <35%
(Note 6)
(Note 6)
V
IN
= 5V, V
RUN
= 0V, V
OUT1
= V
OUT2
= 0V
V
OUT
Ramping Down, MODE/SYNC = 0V
MIN
0.95
TYP
1.2
0.35
0.30
0.01
–8.5
100
262,144
0.3
0
V
IN
– 0.5
1
0.01
1.5
1
0.5
V
IN
200
MAX
1.6
0.45
0.45
1
UNITS
A
Ω
Ω
μA
%
Ω
Cycles
V
μA
V
V
Note 3:
The LTC3407-3 is tested in a proprietary test mode that connects
the output of the error amplifier to an outside servo loop.
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
T
A
= 25°C unless otherwise specified.
Load Step
Pulse-Skipping Mode
V
OUT
200mV/DIV
I
L
500mA/DIV
I
LOAD
500mA/DIV
V
OUT
20mV/DIV
V
OUT
20mV/DIV
I
L
200mA/DIV
V
IN
= 3.6V
V
OUT
= 1.8V
I
LOAD
= 100mA
2μs/DIV
34073 G01
I
L
200mA/DIV
V
IN
= 3.6V
V
OUT
= 1.8V
I
LOAD
= 20mA
1μs/DIV
34073 G02
V
IN
= 3.6V
20μs/DIV
V
OUT
= 1.8V
I
LOAD
= 80mA TO 800mA
CIRCUIT OF FIGURE 1
34073 G03
34073fb
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LTC3407-3
TYPICAL PERFORMANCE CHARACTERISTICS
Load Step
2.5
V
OUT
200mV/DIV
2.4
I
L
500mA/DIV
I
LOAD
500mA/DIV
FREQUENCY (MHz)
T
A
= 25°C unless otherwise specified.
Oscillator Frequency Deviation
vs Supply Voltage
10
8
FREQUENCY DEVIATION (%)
6
4
2
0
–2
–4
–6
–8
Oscillator Frequency vs
Temperature
V
IN
= 3.6V
2.3
2.2
V
IN
= 5V
20μs/DIV
V
OUT
= 3.3V
I
LOAD
= 80mA TO 800mA
CIRCUIT OF FIGURE 1
34073 G04
2.1
2.0
–50 –25
–10
50
25
75
0
TEMPERATURE (°C)
100
125
2
3
4
SUPPLY VOLTAGE (V)
5
6
34073 G06
34073 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
450
400
R
DS(ON)
vs Input Voltage
550
500
450
R
DS(ON)
(mΩ)
MAIN
SWITCH
350
300
250
200
SYNCHRONOUS
SWITCH
R
DS(ON)
(mΩ)
400
350
300
250
200
150
R
DS(ON)
vs Temperature
V
IN
= 3.6V
V
IN
= 4.2V
50
25
75
0
TEMPERATURE (°C)
100
125
1
2
3
4
V
IN
(V)
5
6
7
34073 G08
100
–50 –25
MAIN SWITCH
SYNCHRONOUS SWITCH
0
25 50 75 100 125 150
TEMPERATURE (°C)
34073 G09
34073 G07
Efficiency vs V
IN
100
95
90
EFFICIENCY (%)
85
80
75
70
65
60
55
50
2
V
OUT
= 1.8V
Burst Mode OPERATION
CH2 OFF
3
4
INPUT VOLTAGE (V)
34073 G10
Efficiency vs Load Current
100
95
100
Efficiency vs Load Current
10mA
100mA
EFFICIENCY (%)
800mA
1mA
Burst Mode OPERATION
90
85
80
75
70
65
60
5
6
1
PULSE-SKIPPING
MODE
V
IN
= 5V,
V
OUT
= 3.3V
NO LOAD ON
OTHER CHANNEL
10
100
LOAD CURRENT (mA)
1000
34073 G14
90
EFFICIENCY (%)
Burst Mode OPERATION
80
PULSE-SKIPPING
MODE
70
V
IN
= 3.6V, V
OUT
= 1.8V
NO LOAD ON OTHER CHANNEL
1
10
100
LOAD CURRENT (mA)
1000
34073 G11
60
34073fb
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LTC3407-3
TYPICAL PERFORMANCE CHARACTERISTICS
Load Regulation
4
3
2
V
OUT
ERROR (%)
V
OUT
ERROR (%)
Burst Mode OPERATION
1
0
PULSE-SKIPPING
–1 MODE
–2
–3
–4
1
V
IN
= 3.6V, V
OUT
= 1.8V
NO LOAD ON OTHER CHANNEL
10
100
LOAD CURRENT (mA)
1000
34073 G12
T
A
= 25°C unless otherwise specified.
Load Regulation
4
3
2
V
OUT
ERROR (%)
1
0
PULSE-SKIPPING
–1 MODE
–2
–3
–4
1
V
IN
= 5V, V
OUT
= 3.3V
NO LOAD ON OTHER CHANNEL
10
100
LOAD CURRENT (mA)
1000
34073 G13
Line Regulation
V
OUT
= 1.8V
0.60 I
OUT
= 200mA
0.40
0.20
0
–0.20
–0.40
–0.60
–0.80
–1.00
2
3
4
V
IN
(V)
34073 G15
0.80
Burst Mode OPERATION
5
6
PIN FUNCTIONS
V
OUT1
(Pin 1):
Output Voltage Feedback Pin for Channel
1. An internal resistive divider divides the output voltage
down for comparison to the internal reference voltage.
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. Do not float this pin.
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 operation
of the device. When tied to V
IN
or GND, Burst Mode opera-
tion or pulse-skipping mode is selected, respectively. The
oscillation frequency can be synchronized to an external
oscillator applied to this pin and pulse-skipping mode is
automatically selected. Do not float this pin.
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 falls below
–8.5% of regulation and goes high after 117ms 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. Do not float this pin.
V
OUT2
(Pin 10):
Output Voltage Feedback Pin for Channel 2.
An internal resistive divider divides the output voltage down
for comparison to the internal reference voltage.
Exposed Pad (GND) (Pin 11):
Power Ground. Connect to
the (–) terminal of C
OUT
, and (–) terminal of C
IN
. Must be
connected to electrical ground on PCB.
34073fb
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