LTC3407-2
Dual Synchronous, 800mA,
2.25MHz Step-Down
DC/DC Regulator
FEATURES
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DESCRIPTIO
High Efficiency: Up to 95%
Very Low Quiescent Current: Only 40µA
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
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
The LTC
®
3407-2 is a dual, constant frequency, synchro-
nous step down DC/DC converter. Intended for low power
applications, it operates from 2.5V 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
≤1.2mm.
Each output voltage is adjustable
from 0.6V to 5V. 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 Skip 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.
, LTC and LT are registered trademarks of Linear Technology Corporation.
Burst Mode is a registered trademark of Linear Technology Corporation.
APPLICATIO S
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PDAs/Palmtop PCs
Digital Cameras
Cellular Phones
Portable Media Players
PC Cards
Wireless and DSL Modems
TYPICAL APPLICATIO
V
IN
= 2.5V*
TO 5.5V
C1
10µF
RUN2
V
IN
RUN1
POR
R5
100k
RESET
EFFICIENCY (%)
MODE/SYNC
L2
2.2µH
SW2
C5, 22pF
LTC3407-2
V
OUT2
= 2.5V
AT 800mA
L1
2.2µH
SW1
C4, 22pF
V
OUT1
= 1.8V
AT 800mA
C3
10µF
R4
887k
V
FB2
R3
280k
GND
V
FB1
R2
R1 604k
301k
C2
10µF
C1, C2, C3: TAIYO YUDEN JMK316BJ106ML
L1, L2: MURATA LQH32CN2R2M33
*V
OUT
CONNECTED TO V
IN
FOR V
IN
≤
2.8V
3407 TA01
Figure 1. 2.5V/1.8V at 800mA Step-Down Regulators
sn34072 34072fs
U
LTC3407-2 Efficiency Curve
100
95
90
85
80
75
70
65
60
1
V
IN
= 3.3V
Burst Mode OPERATION
NO LOAD ON OTHER CHANNEL
10
100
LOAD CURRENT (mA)
1000
3407 TA02
U
U
2.5V
1.8V
1
LTC3407-2
ABSOLUTE
(Note 1)
AXI U RATI GS
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
Lead Temperature (Soldering, 10 sec)
LTC3407-2EMSE only ...................................... 300°C
Reflow Peak Body Temperature ............................ 260°C
V
IN
Voltages.................................................– 0.3V to 6V
V
FB1
, V
FB2
, RUN1, RUN2
Voltages ..................................... – 0.3V to V
IN
+ 0.3V
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
PACKAGE/ORDER I FOR ATIO
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
ORDER PART
NUMBER
LTC3407EDD-2
DD PACKAGE
10-LEAD (3mm
×
3mm) PLASTIC DFN
DD PIN 11, EXPOSED PAD: PGND
MUST BE CONNECTED TO GND
DD PART MARKING
LBFB
T
JMAX
= 125°C,
θ
JA
= 45°C/W,
θ
JC
= 10°C/W
Consult LTC Marketing for parts specified with wider operating temperature ranges.
The
●
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
∆V
LINE REG
∆V
LOAD REG
I
S
PARAMETER
Operating Voltage Range
Feedback Pin Input Current
Feedback Voltage (Note 3)
Reference Voltage Line Regulation
Output Voltage Load Regulation
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
V
IN
= 3V, V
FBX
= 0.5V, Duty Cycle <35%
(Note 6)
(Note 6)
V
IN
= 5V, V
RUN
= 0V, V
FBX
= 0V
0.95
0°C
≤
T
A
≤
85°C
–40°C
≤
T
A
≤
85°C
V
IN
= 2.5V to 5.5V (Note 3)
(Note 3)
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
●
ELECTRICAL CHARACTERISTICS
CONDITIONS
●
●
●
f
OSC
f
SYNC
I
LIM
R
DS(ON)
I
SW(LKG)
2
U
U
W
W W
U
W
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
ORDER PART
NUMBER
LTC3407EMSE-2
11
MSE PACKAGE
10-LEAD PLASTIC MSOP
MSE PIN 11, EXPOSED PAD: PGND
MUST BE CONNECTED TO GND
T
JMAX
= 125°C,
θ
JA
= 45°C/W,
θ
JC
= 10°C/W
MSE PART MARKING
LTBDZ
MIN
2.5
0.588
0.585
TYP
MAX
5.5
30
UNITS
V
nA
V
V
%/V
%
0.6
0.6
0.3
0.5
700
40
0.1
0.612
0.612
0.5
950
60
1
2.7
1.6
0.45
0.45
1
µA
µA
µA
MHz
MHz
A
Ω
Ω
µA
1.8
2.25
2.25
1.2
0.35
0.30
0.01
sn34072 34072fs
LTC3407-2
The
●
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
POR
PARAMETER
Power-On Reset Threshold
Power-On Reset On-Resistance
Power-On Reset Delay
V
RUN
I
RUN
RUN Threshold
RUN Leakage Current
●
●
ELECTRICAL CHARACTERISTICS
CONDITIONS
V
FBX
Ramping Up, MODE/SYNC = 0V
V
FBX
Ramping Down, MODE/SYNC = 0V
MIN
TYP
8.5
–8.5
100
262,144
MAX
UNITS
%
%
200
1.5
1
Ω
Cycles
V
µA
0.3
1
0.01
Note 1:
Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
Note 2:
The LTC3407-2E 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 LTC3407-2 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 PERFOR A CE CHARACTERISTICS
Burst Mode Operation
SW
5V/DIV
SW
5V/DIV
V
OUT
100mV/DIV
I
L
200mA/DIV
V
IN
= 3.6V
2µs/DIV
V
OUT
= 1.8V
I
LOAD
= 100mA
CIRCUIT OF FIGURE 1
Efficiency vs Input Voltage
100
95
90
1mA
85
800mA
80
75
70
65
60
2
V
OUT
= 1.8V
Burst Mode OPERATION
CIRCUIT OF FIGURE 1
3
4
INPUT VOLTAGE (V)
3407 G04
FREQUENCY (MHz)
10mA
FREQUENCY DEVIATION (%)
100mA
EFFICIENCY (%)
5
U W
6
T
A
= 25°C unless other wise specified.
Load Step
V
OUT
200mV/DIV
Pulse Skipping Mode
V
OUT
10mV/DIV
I
L
200mA/DIV
I
L
500mA/DIV
I
LOAD
500mA/DIV
3407 G01
V
IN
= 3.6V
1µs/DIV
V
OUT
= 1.8V
I
LOAD
= 20mA
CIRCUIT OF FIGURE 1
3407 G02
V
IN
= 3.6V
20µs/DIV
V
OUT
= 1.8V
I
LOAD
= 80mA TO 800mA
CIRCUIT OF FIGURE 1
3407 G03
Oscillator Frequency vs
Temperature
2.5
V
IN
= 3.6V
10
8
6
4
2
0
–2
–4
–6
–8
2.0
–50 –25
–10
50
25
75
0
TEMPERATURE (°C)
100
125
Oscillator Frequency vs Supply
Voltage
2.4
2.3
2.2
2.1
2
3
4
SUPPLY VOLTAGE (V)
5
6
3407 G06
3407 G05
sn34072 34072fs
3
LTC3407-2
TYPICAL PERFOR A CE CHARACTERISTICS
Reference Voltage vs
Temperature
0.615
V
IN
= 3.6V
0.610
REFERENCE VOLTAGE (V)
R
DS(ON)
(mΩ)
R
DS(ON)
(mΩ)
0.605
0.600
0.595
0.590
0.585
–50 –25
50
25
75
0
TEMPERATURE (°C)
Efficiency vs Load Current
100
2.7V
95
90
EFFICIENCY (%)
3.6V
4.2V
EFFICIENCY (%)
V
OUT
ERROR (%)
85
80
75
70 V
OUT
= 2.5V
Burst Mode OPERATION
65 NO LOAD ON OTHER CHANNEL
CIRCUIT OF FIGURE 1
60
1
10
100
LOAD CURRENT (mA)
Efficiency vs Load Current
100
95
90
EFFICIENCY (%)
3.6V
EFFICIENCY (%)
85
80
75
70
2.7V
85
80
75
70
4.2V
V
OUT
ERROR (%)
4.2V
V
OUT
= 1.2V
Burst Mode OPERATION
65
NO LOAD ON OTHER CHANNEL
CIRCUIT OF FIGURE 1
60
1
10
100
LOAD CURRENT (mA)
4
U W
100
3407 G07
3407 G10
3407 G13
R
DS(ON)
vs Input Voltage
500
T
A
= 25°C
450
450
400
350
300
250
200
125
1
2
SYNCHRONOUS
SWITCH
MAIN
SWITCH
400
350
300
250
200
150
3
4
V
IN
(V)
5
6
7
3407 G08
R
DS(ON)
vs Temperature
550
500
V
IN
= 4.2V
V
IN
= 2.7V
V
IN
= 3.6V
100
–50 –25
MAIN SWITCH
SYNCHRONOUS SWITCH
0
25 50 75 100 125 150
TEMPERATURE (°C)
3407 G09
Efficiency vs Load Current
100
95
90
85
80
75
PULSE SKIP MODE
70
65
60
1000
1
V
IN
= 3.6V, V
OUT
= 1.8V
NO LOAD ON OTHER CHANNEL
10
100
LOAD CURRENT (mA)
1000
3407 G11
Load Regulation
4
3
Burst Mode OPERATION
2
1
0
PULSE SKIP MODE
–1
–2
–3
–4
1
V
IN
= 3.6V, V
OUT
= 1.8V
NO LOAD ON OTHER CHANNEL
10
100
LOAD CURRENT (mA)
1000
3407 G12
Burst Mode OPERATION
Efficiency vs Load Current
100
95
90
2.7V
3.6V
0.5
0.4
0.3
0.2
0.1
0
–0.1
–0.2
–0.3
–0.4
–0.5
1000
3407 G14
Line Regulation
V
OUT
= 1.8V
I
OUT
= 200mA
T
A
= 25°C
1000
V
OUT
= 1.5V
Burst Mode OPERATION
65
NO LOAD ON OTHER CHANNEL
CIRCUIT OF FIGURE 1
60
1
10
100
LOAD CURRENT (mA)
2
3
4
V
IN
(V)
5
6
3407 G15
sn34072 34072fs
LTC3407-2
PI FU CTIO S
V
FB1
(Pin 1):
Output Feedback. Receives the feedback
voltage 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 regu-
lator 1 to shut down.
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):
Main Ground. Connect to the (–) terminal of
C
OUT
, and (–) terminal of C
IN
.
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
operation or pulse skipping mode is selected, respec-
tively. Do not float this pin. The oscillation frequency can
be syncronized 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 117ms
when both channels are within regulation.
RUN2 (Pin 9):
Output Feedback. Forcing this pin to V
IN
enables regulator 2, while forcing it to GND causes regu-
lator 2 to shut down.
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
connected to electrical ground on PCB.
U
U
U
sn34072 34072fs
5
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