LTC3406B-2
2.25MHz, 600mA
Synchronous Step-Down
Regulator in ThinSOT
TM
FEATURES
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DESCRIPTIO
High Efficiency: Up to 96%
600mA Output Current at V
IN
= 3V
2.5V to 5.5V Input Voltage Range
2.25MHz Constant Frequency Operation
No Schottky Diode Required
Low Dropout Operation: 100% Duty Cycle
Low Quiescent Current: 350µA
0.6V Reference Allows Low Output Voltages
Shutdown Mode Draws < 1µA Supply Current
Current Mode Operation for Excellent Line and
Load Transient Response
Overtemperature Protected
Low Profile (1mm) SOT-23 Package
The LTC
®
3406B-2 is a high efficiency monolithic synchro-
nous buck regulator using a constant frequency, current
mode architecture. Supply current with no load is 350µA,
dropping to <1µA in shutdown. The 2.5V to 5.5V input
voltage range makes the LTC3406B-2 ideally suited for
single Li-Ion battery-powered applications. 100% duty
cycle capability provides low dropout operation, extend-
ing battery life in portable systems. PWM pulse skipping
mode operation provides very low output ripple voltage for
noise sensitive applications.
The switching frequency is internally set at 2.25MHz, allow-
ing the use of tiny surface mount inductors and capacitors.
The internal synchronous switch increases efficiency and
eliminates the need for an external Schottky diode. Low
output voltages are easily supported with the 0.6V feedback
reference voltage. The LTC3406B-2 is available in a low pro-
file (1mm) SOT-23 package. Refer to LTC3406 for appli-
cations that require Burst Mode
®
operation.
, LTC and LT are registered trademarks of Linear Technology Corporation.
Burst Mode is a registered trademark of Linear Technology Corporation.
ThinSOT is a trademark of Linear Technology Corporation.
Protected by U.S. Patents, including 6580258, 5481178.
APPLICATIO S
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Cellular Telephones
Personal Information Appliances
Wireless and DSL Modems
Digital Still Cameras
MP3 Players
Portable Instruments
TYPICAL APPLICATIO
High Efficiency Step-Down Converter
100
V
IN
2.7V
TO 5.5V
2.2µH*
V
IN
4.7µF
CER
SW
22pF
1M
10µF
CER
V
OUT
1.8V
600mA
90
80
V
OUT
= 1.8V
T
A
= 25°C
LTC3406B-2
RUN
GND
V
FB
EFFICIENCY (%)
70
60
50
40
30
20
10
0.1
V
IN
= 4.2V
1
100
10
OUTPUT CURRENT (mA)
1000
3406B TA01b
499k
3406B TA01a
U
Efficiency vs Load Current
V
IN
= 3.6V
V
IN
= 2.7V
sn3406b2 3406b2fs
U
U
1
LTC3406B-2
ABSOLUTE
(Note 1)
AXI U
RATI GS
PACKAGE/ORDER I FOR ATIO
TOP VIEW
RUN 1
GND 2
SW 3
4 V
IN
5 V
FB
Input Supply Voltage .................................. – 0.3V to 6V
RUN, V
FB
Voltages ..................................... – 0.3V to V
IN
SW Voltage (DC) ......................... – 0.3V to (V
IN
+ 0.3V)
P-Channel Switch Source Current (DC) ............. 800mA
N-Channel Switch Sink Current (DC) ................. 800mA
Peak SW Sink and Source Current ........................ 1.3A
Operating Temperature Range (Note 2) .. – 40°C to 85°C
Maximum Junction Temperature (Notes 3, 6) ..... 125°C
Storage Temperature Range ................ – 65°C to 150°C
Lead Temperature (Soldering, 10 sec)................. 300°C
ORDER PART
NUMBER
LTC3406B-2ES5
S5 PART MARKING
LTAGH
S5 PACKAGE
5-LEAD PLASTIC TSOT-23
T
JMAX
= 125°C,
θ
JA
= 250°C/ W,
θ
JC
= 90°C/ W
Consult LTC Marketing for parts specified with wider operating temperature ranges.
The
●
denotes specifications which apply over the full operating
temperature range, otherwise specifications are T
A
= 25°C. V
IN
= 3.6V unless otherwise specified.
SYMBOL
I
VFB
V
FB
PARAMETER
Feedback Current
Regulated Feedback Voltage
(Note 4) T
A
= 25°C
(Note 4) 0°C
≤
T
A
≤
85°C
(Note 4) –40°C
≤
T
A
≤
85°C
V
IN
= 2.5V to 5.5V (Note 4)
∆V
OVL
= V
OVL
– V
FB
, LTC3406B
V
IN
= 3V, V
FB
= 0.5V or V
OUT
= 90%,
Duty Cycle < 35%
●
ELECTRICAL CHARACTERISTICS
CONDITIONS
MIN
0.5880
0.5865
0.5850
20
0.75
TYP
0.6
0.6
0.6
0.04
50
1
0.5
MAX
±30
0.6120
0.6135
0.6150
0.4
80
1.25
UNITS
nA
V
V
V
%/V
mV
A
%
●
●
●
∆V
FB
∆V
OVL
I
PK
V
LOADREG
V
IN
I
S
Reference Voltage Line Regulation
∆Output
Overvoltage Lockout
Peak Inductor Current
Output Voltage Load Regulation
Input Voltage Range
Input DC Bias Current
Shutdown
2.5
350
0.1
5.5
500
1
2.7
0.5
0.45
±1
1.5
±1
(Note 5)
V
FB
= 0.5V or V
OUT
= 90%
V
RUN
= 0V, V
IN
= 4.2V
V
FB
= 0.6V or V
OUT
= 100%
V
FB
= 0V or V
OUT
= 0V
I
SW
= 100mA
I
SW
= –100mA
V
RUN
= 0V, V
SW
= 0V or 5V, V
IN
= 5V
●
●
●
f
OSC
R
PFET
R
NFET
I
LSW
V
RUN
I
RUN
Oscillator Frequency
R
DS(ON)
of P-Channel FET
R
DS(ON)
of N-Channel FET
SW Leakage
RUN Threshold
RUN Leakage Current
1.8
2.25
310
0.4
0.35
±0.01
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 LTC3406B-2ES5 is guaranteed to meet performance
specifications from 0°C to 70°C. Specifications over the –40°C to 85°C
operating temperature range are assured by design, characterization and
correlation with statistical process controls.
Note 3:
T
J
is calculated from the ambient temperature T
A
and power
dissipation P
D
according to the following formula:
LTC3406B-2ES5: T
J
= T
A
+ (P
D
)(250°C/W)
Note 4:
The LTC3406B-2ES5 is tested in a proprietary test mode that
connects V
FB
to the output of the error amplifier.
Note 5:
Dynamic supply current is higher due to the gate charge being
delivered at the switching frequency.
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.
sn3406b2 3406b2fs
2
U
V
µA
µA
MHz
kHz
Ω
Ω
µA
V
µA
W
U
U
W W
W
LTC3406B-2
TYPICAL PERFOR A CE CHARACTERISTICS
(From Figure 1a Except for the Resistive Divider Resistor Values)
Efficiency vs Input Voltage
100
95
90
EFFICIENCY (%)
T
A
= 25°C
I
OUT
= 100mA
EFFICIENCY (%)
85
80
I
OUT
= 600mA
V
IN
= 3.6V
V
IN
= 2.7V
V
IN
= 4.2V
EFFICIENCY (%)
I
OUT
= 10mA
75
70
65
2
3
5
4
INPUT VOLTAGE (V)
6
3406B G01
Efficiency vs Output Current
100
90
80
V
OUT
= 2.5V
T
A
= 25°C
0.614
REFERENCE VOLTAGE (V)
EFFICIENCY (%)
70
60
50
40
30
20
10
0.1
1
100
10
OUTPUT CURRENT (mA)
1000
3406B G04
0.604
0.599
0.594
0.589
0.584
–50 –25
FREQUENCY (MHz)
V
IN
= 2.7V
V
IN
= 4.2V
V
IN
= 3.6V
Oscillator Frequency vs
Supply Voltage
2.70
OSCILLATOR FREQUENCY (MHz)
T
A
= 25°C
2.55
OUTPUT VOLTAGE (V)
2.40
2.25
2.10
1.95
1.80
1.814
1.804
1.794
1.784
1.774
0
100 200 300 400 500 600 700 800 900
LOAD CURRENT (mA)
3406B G08
R
DS(ON)
(Ω)
2
3
4
5
SUPPLY VOLTAGE (V)
U W
6
3406B G07
Efficiency vs Output Current
100
90
80
70
60
50
40
30
20
10
0.1
1
100
10
OUTPUT CURRENT (mA)
1000
3406B G02
Efficiency vs Output Current
100
V
OUT
= 1.5V
90 T
A
= 25°C
80
70
60
50
40
30
20
10
0.1
1
100
10
OUTPUT CURRENT (mA)
1000
3406B G03
V
OUT
= 1.2V
T
A
= 25°C
V
IN
= 3.6V
V
IN
= 2.7V
V
IN
= 4.2V
Reference Voltage vs
Temperature
2.55
V
IN
= 3.6V
0.609
Oscillator Frequency vs
Temperature
V
IN
= 3.6V
2.40
2.25
2.10
50
25
75
0
TEMPERATURE (°C)
100
125
1.95
–50 –25
50
25
75
0
TEMPERATURE (°C)
100
125
3406B G05
3406B G06
Output Voltage vs Load Current
1.844
1.834
1.824
V
IN
= 3.6V
T
A
= 25°C
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
R
DS(ON
) vs Input Voltage
T
A
= 25°C
MAIN
SWITCH
SYNCHRONOUS
SWITCH
0
1
5
4
2
3
INPUT VOLTAGE (V)
6
7
3406B G09
sn3406b2 3406b2fs
3
LTC3406B-2
TYPICAL PERFOR A CE CHARACTERISTICS
(From Figure 1a Except for the Resistive Divider Resistor Values)
Dynamic Supply Current vs
Supply Voltage
450
R
DS(ON)
vs Temperature
0.7
V
IN
= 2.7V
V
IN
= 4.2V
0.5
R
DS(ON)
(Ω)
V
IN
= 3.6V
DYNAMIC SUPPLY CURRENT (µA)
DYNAMIC SUPPLY CURRENT (µA)
0.6
0.4
0.3
0.2
0.1
0
–50 –25
MAIN SWITCH
SYNCHRONOUS SWITCH
50
25
75
0
TEMPERATURE (°C)
100
125
Switch Leakage vs Temperature
300
V
IN
= 5.5V
RUN = 0V
250
SWITCH LEAKAGE (nA)
SWITCH LEAKAGE (pA)
200
150
100
50
0
–50 –25
MAIN SWITCH
SYNCHRONOUS SWITCH
50
25
75
0
TEMPERATURE (°C)
100
125
Start-Up from Shutdown
RUN
5V/DIV
V
OUT
1V/DIV
AC COUPLED
I
L
500mA/DIV
V
OUT
100mV/DIV
AC COUPLED
I
L
500mA/DIV
I
LOAD
500mA/DIV
V
IN
= 3.6V
40µs/DIV
V
OUT
= 1.8V
I
LOAD
= 600mA (LOAD: 3Ω RESISTOR)
4
U W
3406B G10
3406B G13
Dynamic Supply Current vs
Temperature
390
V
IN
= 3.6V
V
OUT
= 1.8V
370 I
LOAD
= 0A
350
330
310
290
270
250
–50
V
OUT
= 1.8V
430 I
LOAD
= 0A
T
A
= 25°C
410
390
370
350
330
310
290
270
250
2
2.5
3
3.5 4 4.5
5
SUPPLY VOLTAGE (V)
5.5
6
50
0
TEMPERATURE (°C)
100
125
3406B G11
3406B
G12
Switch Leakage vs Input Voltage
120
100
80
60
40
20
0
RUN = 0V
T
A
= 25°C
SYNCHRONOUS
SWITCH
Discontinuous Operation
SW
2V/DIV
V
OUT
10mV/DIV
AC COUPLED
I
L
100mA/DIV
MAIN
SWITCH
V
IN
= 3.6V
V
OUT
= 1.8V
I
LOAD
= 50mA
1µs/DIV
3406B G15
0
1
2
3
4
INPUT VOLTAGE (V)
5
6
3406B G14
Load Step
V
OUT
100mV/DIV
AC COUPLED
I
L
500mA/DIV
I
LOAD
500mA/DIV
Load Step
3406B G16
V
IN
= 3.6V
20µs/DIV
V
OUT
= 1.8V
I
LOAD
= 0mA TO 600mA
3406B G17
V
IN
= 3.6V
20µs/DIV
V
OUT
= 1.8V
I
LOAD
= 50mA TO 600mA
3406B G18
sn3406b2 3406b2fs
LTC3406B-2
TYPICAL PERFOR A CE CHARACTERISTICS
(From Figure 1a Except for the Resistive Divider Resistor Values)
Load Step
V
OUT
100mV/DIV
AC COUPLED
I
L
500mA/DIV
I
LOAD
500mA/DIV
V
OUT
100mV/DIV
AC COUPLED
I
L
500mA/DIV
I
LOAD
500mA/DIV
V
IN
= 3.6V
20µs/DIV
V
OUT
= 1.8V
I
LOAD
= 100mA TO 600mA
PI FU CTIO S
RUN (Pin 1):
Run Control Input. Forcing this pin above
1.5V enables the part. Forcing this pin below 0.3V shuts
down the device. In shutdown, all functions are disabled
drawing <1µA supply current. Do not leave RUN floating.
GND (Pin 2):
Ground Pin.
SW (Pin 3):
Switch Node Connection to Inductor. This pin
connects to the drains of the internal main and synchro-
nous power MOSFET switches.
V
IN
(Pin 4):
Main Supply Pin. Must be closely decoupled
to GND, Pin 2, with a 2.2µF or greater ceramic capacitor.
V
FB
(Pin 5):
Feedback Pin. Receives the feedback voltage
from an external resistive divider across the output.
U W
Load Step
3406B G19
V
IN
= 3.6V
20µs/DIV
V
OUT
= 1.8V
I
LOAD
= 200mA TO 600mA
3406B G20
U
U
U
sn3406b2 3406b2fs
5
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