LTC3411
1.25A, 4MHz, Synchronous
Step-Down DC/DC Converter
FEATURES
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DESCRIPTIO
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Small 10-Lead MSOP or DFN Package
Uses Tiny Capacitors and Inductor
High Frequency Operation: Up to 4MHz
High Switch Current: 1.6A
Low R
DS(ON)
Internal Switches: 0.110Ω
High Efficiency: Up to 95%
Stable with Ceramic Capacitors
Current Mode Operation for Excellent Line
and Load Transient Response
Short-Circuit Protected
Low Dropout Operation: 100% Duty Cycle
Low Shutdown Current: I
Q
≤
1µA
Low Quiescent Current: 60µA
Output Voltages from 0.8V to 5V
Selectable Burst Mode
®
Operation
Sychronizable to External Clock
The LTC
®
3411 is a constant frequency, synchronous,
step- down DC/DC converter. Intended for medium power
applications, it operates from a 2.63V to 5.5V input voltage
range and has a user configurable operating frequency up
to 4MHz, allowing the use of tiny, low cost capacitors and
inductors 2mm or less in height. The output voltage is
adjustable from 0.8V to 5V. Internal sychronous 0.11Ω
power switches with 1.6A peak current ratings provide
high efficiency. The LTC3411’s current mode architecture
and external compensation allow the transient response
to be optimized over a wide range of loads and output
capacitors.
The LTC3411 can be configured for automatic power
saving Burst Mode operation to reduce gate charge losses
when the load current drops below the level required for
continuous operation. For reduced noise and RF interfer-
ence, the SYNC/MODE pin can be configured to skip
pulses or provide forced continuous operation.
To further maximize battery life, the P-channel MOSFET is
turned on continuously in dropout (100% duty cycle) with
a low quiescent current of 60µA. 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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Notebook Computers
Digital Cameras
Cellular Phones
Handheld Instruments
Board Mounted Power Supplies
TYPICAL APPLICATIO
V
IN
2.63V TO 5.5V
C1
22µF
V
IN
SYNC/MODE
PGOOD
LTC3411
I
TH
13k
1000pF
324k
SHDN/R
T
SGND
PGND
412k
V
FB
PV
IN
SV
IN
SW
887k
L1
2.2µH
Efficiency vs Load Current
100
95
EFFICIENCY (%)
V
OUT
2.5V/1.25A
C2
22µF
90
85
80
75
V
IN
= 3.3V
V
OUT
= 2.5V
f
O
= 1MHz
Burst Mode OPERATION
1
100
10
LOAD CURRENT (mA)
1000
3411 TA01
NOTE: IN DROPOUT, THE OUTPUT TRACKS
THE INPUT VOLTAGE
C1, C2: TAIYO YUDEN JMK325BJ226MM
L1: TOKO A914BYW-2R2M (D52LC SERIES)
3411 F01
70
Figure 1. Step-Down 2.5V/1.25A Regulator
U
sn3411 3411fs
U
U
1
LTC3411
ABSOLUTE
AXI U RATI GS
PV
IN
, SV
IN
Voltages .....................................– 0.3V to 6V
V
FB
, I
TH
, SHDN/R
T
Voltages .......... – 0.3V to (V
IN
+ 0.3V)
SYNC/MODE Voltage .................... – 0.3V to (V
IN
+ 0.3V)
SW Voltage ................................... – 0.3V to (V
IN
+ 0.3V)
PGOOD Voltage ...........................................– 0.3V to 6V
Operating Ambient Temperature Range
(Note 2) .................................................. – 40°C to 85°C
PACKAGE/ORDER I FOR ATIO
TOP VIEW
SHDN/R
T
SYNC/MODE
SGND
SW
PGND
1
2
3
4
5
10 I
TH
9 V
FB
8 PGOOD
7 SV
IN
6 PV
IN
ORDER PART
NUMBER
LTC3411EDD
DD PART MARKING
LADT
SHDN/R
T
SYNC/MODE
SGND
SW
PGND
1
2
3
4
5
DD PACKAGE
10-LEAD (3mm
×
3mm) PLASTIC DFN
T
JMAX
= 125°C,
θ
JA
= 43°C/W,
θ
JC
= 3°C/W
(EXPOSED PAD MUST BE SOLDERED TO PCB)
Consult LTC Marketing for parts specified with wider operating temperature ranges.
The
q
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
IN
= 3.3V, R
T
= 324k unless otherwise specified. (Note 2)
SYMBOL
V
IN
I
FB
V
FB
∆V
LINEREG
∆V
LOADREG
g
m(EA)
I
S
PARAMETER
Operating Voltage Range
Feedback Pin Input Current
Feedback Voltage
Reference Voltage Line Regulation
Output Voltage Load Regulation
Error Amplifier Transconductance
Input DC Supply Current (Note 4)
Active Mode
Sleep Mode
Shutdown
Shutdown Threshold High
Active Oscillator Resistor
Oscillator Frequency
Synchronization Frequency
Peak Switch Current Limit
Top Switch On-Resistance (Note 6)
Bottom Switch On-Resistance (Note 6)
Switch Leakage Current
Undervoltage Lockout Threshold
CONDITIONS
(Note 3)
(Note 3)
V
IN
= 2.7V to 5V
I
TH
= 0.36, (Note 3)
I
TH
= 0.84, (Note 3)
I
TH
Pin Load =
±5µA
(Note 3)
V
FB
= 0.75V, SYNC/MODE = 3.3V
V
SYNC/MODE
= 3.3V, V
FB
= 1V
V
SHDN/RT
= 3.3V
MIN
2.625
q
q
q
ELECTRICAL CHARACTERISTICS
V
SHDN/RT
f
OSC
f
SYNC
I
LIM
R
DS(ON)
I
SW(LKG)
V
UVLO
R
T
= 324k
(Note 7)
(Note 7)
I
TH
= 1.3
V
IN
= 3.3V
V
IN
= 3.3V
V
IN
= 6V, V
ITH/RUN
= 0V, V
FB
= 0V
V
IN
Ramping Down
2
U
U
W
W W
U
W
(Note 1)
Junction Temperature (Notes 5, 8) ....................... 125°C
Storage Temperature Range
DD Package ...................................... – 65°C to 125°C
MS Package .................................... – 65°C to 150°C
Lead Temperature (Soldering, 10 sec).................. 300°C
TOP VIEW
10
9
8
7
6
I
TH
V
FB
PGOOD
SV
IN
PV
IN
ORDER PART
NUMBER
LTC3411EMS
MS PART MARKING
LTQT
MS PACKAGE
10-LEAD PLASTIC MSOP
T
JMAX
= 125°C,
θ
JA
= 120°C/W,
θ
JC
= 10°C/W
TYP
0.784
0.8
0.04
0.02
– 0.02
800
MAX
5.5
±0.1
0.816
0.2
0.2
– 0.2
UNITS
V
µA
V
%/V
%
%
µS
µA
µA
µA
V
Ω
MHz
MHz
MHz
A
Ω
Ω
µA
V
0.85
0.4
1.6
2.375
240
350
62
100
0.1
1
V
IN
– 0.6 V
IN
– 0.4
324k
1M
1
1.15
4
4
2
0.11
0.15
0.11
0.15
0.01
1
2.5
2.625
sn3411 3411fs
LTC3411
The
q
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
IN
= 3.3V, R
T
= 324k unless otherwise specified. (Note 2)
SYMBOL
PGOOD
R
PGOOD
PARAMETER
Power Good Threshold
Power Good Pull-Down On-Resistance
CONDITIONS
V
FB
Ramping Up, SHDN/R
T
= 1V
V
FB
Ramping Down, SHDN/R
T
= 1V
MIN
TYP
6.8
– 7.6
118
MAX
UNITS
%
%
Ω
ELECTRICAL CHARACTERISTICS
200
Note 1:
Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
Note 2:
The LTC3411E is guaranteed to meet specified performance from
0°C to 70°C. Specifications over the – 40°C to 85°C operating ambient
termperature range are assured by design, characterization and correlation
with statistical process controls.
Note 3:
The LTC3411 is tested in a feedback loop which servos V
FB
to the
midpoint for the error amplifier (V
ITH
= 0.6V).
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:
LTC3411EDD: T
J
= T
A
+ (P
D
• 43°C/W)
LTC3411EMS: T
J
= T
A
+ (P
D
• 120°C/W)
Note 6:
Switch on-resistance is guaranteed by correlation to wafer level
measurements.
Note 7:
4MHz operation is guaranteed by design but not production tested
and is subject to duty cycle limitations (see Applications Information).
Note 8:
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.
PI FU CTIO S
SHDN/R
T
(Pin 1):
Combination Shutdown and Timing
Resistor Pin. The oscillator frequency is programmed by
connecting a resistor from this pin to ground. Forcing this
pin to SV
IN
causes the device to be shut down. In shut-
down all functions are disabled.
SYNC/MODE (Pin 2):
Combination Mode Selection and
Oscillator Synchronization Pin. This pin controls the op-
eration of the device. When tied to SV
IN
or SGND, Burst
Mode operation or pulse skipping mode is selected, re-
spectively. If this pin is held at half of SV
IN
, the forced
continuous mode is selected. The oscillation frequency
can be syncronized to an external oscillator applied to this
pin. When synchronized to an external clock pulse skip
mode is selected.
SGND (Pin 3):
The Signal Ground Pin. All small signal
components and compensation components should be
connected to this ground (see Board Layout Consider-
ations).
SW (Pin 4):
The Switch Node Connection to the Inductor.
This pin swings from PV
IN
to PGND.
PGND (Pin 5):
Main Power Ground Pin. Connect to the
(–) terminal of C
OUT
, and (–) terminal of C
IN
.
PV
IN
(Pin 6):
Main Supply Pin. Must be closely decoupled
to PGND.
SV
IN
(Pin 7):
The Signal Power Pin. All active circuitry is
powered from this pin. Must be closely decoupled to
SGND. SV
IN
must be greater than or equal to PV
IN
.
PGOOD (Pin 8):
The Power Good Pin. This common drain
logic output is pulled to SGND when the output voltage is
not within
±7.5%
of regulation.
V
FB
(Pin 9):
Receives the feedback voltage from the
external resistive divider across the output. Nominal volt-
age for this pin is 0.8V.
I
TH
(Pin 10):
Error Amplifier Compensation Point. The
current comparator threshold increases with this control
voltage. Nominal voltage range for this pin is 0V to 1.5V.
U
U
U
sn3411 3411fs
3
LTC3411
PI FU CTIO S
PIN
1
2
3
4
5
6
7
8
9
10
NAME
SHDN/R
T
SYNC/MODE
SGND
SW
PGND
PV
IN
SV
IN
PGOOD
V
FB
I
TH
DESCRIPTION
Shutdown/Timing Resistor
Mode Select/Sychronization Pin
Signal Ground
Switch Node
Main Power Ground
Main Power Supply
Signal Power Supply
Power Good Pin
Output Feedback Pin
Error Amplifier Compensation and Run Pin
NOMINAL (V)
MIN
TYP
MAX
– 0.3
0.8
SV
IN
0
SV
IN
0
0
PV
IN
0
– 0.3
5.5
2.5
5.5
0
SV
IN
0
0.8
1.0
0
1.5
ABSOLUTE MAX (V)
MIN
MAX
– 0.3
SV
IN
+ 0.3
– 0.3
SV
IN
+ 0.3
– 0.3
– 0.3
– 0.3
– 0.3
– 0.3
– 0.3
PV
IN
+ 0.3
SV
IN
+ 0.3
6
6
SV
IN
+ 0.3
SV
IN
+ 0.3
TYPICAL PERFOR A CE CHARACTERISTICS
Burst Mode Operation
V
OUT
10mV/
DIV
V
OUT
10mV/
DIV
I
L1
100mA/
DIV
V
IN
= 3.3V
2µs/DIV
V
OUT
= 2.5V
I
LOAD
= 50mA
CIRCUIT OF FIGURE 7
3411 G01.eps
Efficiency vs Load Current
100
95
90
Burst Mode
OPERATION
100
95
90
EFFICIENCY (%)
EFFICIENCY (%)
85
80
75
70
65
60
1
PULSE SKIP
FORCED CONTINUOUS
V
IN
= 3.3V
V
OUT
= 2.5V
CIRCUIT OF FIGURE 7
100
1000
10
LOAD CURRENT (mA)
10000
3411 G04
4
U W
U
U
U
Pulse Skipping Mode
V
OUT
10mV/
DIV
Forced Continuous Mode
I
L1
100mA/
DIV
2µs/DIV
V
IN
= 3.3V
V
OUT
= 2.5V
I
LOAD
= 50mA
CIRCUIT OF FIGURE 7
3411 G02.eps
I
L1
100mA/
DIV
V
IN
= 3.3V
2µs/DIV
V
OUT
= 2.5V
I
LOAD
= 50mA
CIRCUIT OF FIGURE 7
3411 G03.eps
Efficiency vs V
IN
I
OUT
= 400mA
Load Step
V
OUT
100mV/
DIV
I
OUT
= 1.25A
85
80
75
70
65
V
OUT
= 2.5V
CIRCUIT OF FIGURE 7
3.5
4.5
V
IN
(V)
5.5
3411 G05
I
L1
0.5A/
DIV
V
IN
= 3.3V
40µs/DIV
V
OUT
= 2.5V
I
LOAD
= 0.25mA TO 1.25A
CIRCUIT OF FIGURE 7
3411 G06.eps
60
2.5
sn3411 3411fs
LTC3411
TYPICAL PERFOR A CE CHARACTERISTICS
Load Regulation
0.4
0.3
0.2
Burst Mode
OPERATION
PULSE SKIP
FORCED
CONTINUOUS
V
IN
= 3.3V
V
OUT
= 2.5V
0.50
0.45
0.40
V
OUT
ERROR (%)
V
OUT
ERROR (%)
0.1
0
–0.1
–0.2
–0.3
–0.4
–0.5
1
0.35
0.30
0.25
0.20
0.15
0.10
0.05
0
I
OUT
= 400mA
I
OUT
= 1.25A
FREQUENCY VARIATION (%)
10
100
1000
LOAD CURRENT (mA)
Frequency Variation
vs Temperature
10
8
REFERENCE VARIATION (%)
6
4
EFFICIENCY (%)
R
DS(ON)
(mΩ)
2
0
–2
–4
–6
–8
–10
–50
–25
0
25
50
75
TEMPERATURE (°C)
U W
100
Line Regulation
10
V
OUT
= 1.8V
T
A
= 25°C
8
6
4
2
0
–2
–4
–6
–8
–10
2
3
4
V
IN
(V)
5
6
3411 G08
Frequency vs V
IN
V
OUT
= 1.8V
I
OUT
= 1.25A
T
A
= 25°C
10000
3411 G07
2
3
4
V
IN
(V)
5
6
3411 G09
Efficiency vs Frequency
100
V
IN
= 3.3V
V
OUT
= 2.5V
I
OUT
= 500mA
T
A
= 25°C
120
R
DS(ON)
vs V
IN
T
A
= 25°C
115
110
SYNCHRONOUS SWITCH
105
MAIN SWITCH
100
95
95
90
85
125
0
1
2
3
FREQUENCY (MHz)
4
3411 G11
90
2.5
3
3.5
4
4.5
V
IN
(V)
5
5.5
6
3411 G10
3411 G12
sn3411 3411fs
5
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