LTC3406B
1.5MHz, 600mA
Synchronous Step-Down
Regulator in ThinSOT
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
1.5MHz Constant Frequency Operation
No Schottky Diode Required
Low Dropout Operation: 100% Duty Cycle
Low Quiescent Current: 300µA
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) ThinSOT
TM
Package
The LTC
®
3406B is a high efficiency monolithic synchro-
nous buck regulator using a constant frequency, current
mode architecture. The device is available in an adjustable
version and fixed output voltages of 1.5V and 1.8V. Supply
current with no load is 300µA and drops to <1µA in
shutdown. The 2.5V to 5.5V input voltage range makes the
LTC3406B ideally suited for single Li-Ion battery-powered
applications. 100% duty cycle provides low dropout op-
eration, extending battery life in portable systems. PWM
pulse skipping mode operation provides very low output
ripple voltage for noise sensitive applications.
Switching frequency is internally set at 1.5MHz, allowing
the use of small 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 feed-
back reference voltage. The LTC3406B is available in a low
profile (1mm) ThinSOT package. Refer to LTC3406 for
applications 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
100
90
80
4
C
IN
**
4.7µF
CER
1
V
IN
SW
3
VOUT = 1.8V
EFFICIENCY (%)
V
IN
2.7V
TO 5.5V
2.2µH*
C
OUT
†
10µF
CER
V
OUT
1.8V
600mA
70
60
50
40
30
20
10
0.1
VIN = 3.6V
VIN = 2.7V
LTC3406B-1.8
RUN
2
V
OUT
GND
5
3406B F01a
VIN = 4.2V
*MURATA LQH32CN2R2M33
**TAIYO YUDEN JMK212BJ475MG
†
TAIYO YUDEN JMK316BJ106ML
Figure 1a. High Efficiency Step-Down Converter
Figure 1b. Efficiency vs Load Current
3406bfa
U
1
100
10
OUTPUT CURRENT (mA)
1000
3406B F01b
U
U
1
LTC3406B
ABSOLUTE
AXI U
RATI GS
Input Supply Voltage .................................. – 0.3V to 6V
RUN, V
FB
Voltages ..................................... – 0.3V to V
IN
SW Voltage .................................. – 0.3V to (V
IN
+ 0.3V)
P-Channel Switch Source Current (DC) ............. 800mA
N-Channel Switch Sink Current (DC) ................. 800mA
PACKAGE/ORDER I FOR ATIO
TOP VIEW
RUN 1
GND 2
SW 3
4 V
IN
5 V
FB
ORDER PART
NUMBER
LTC3406BES5
S5 PART MARKING
LTE2
RUN 1
GND 2
SW 3
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
LTC3406B (Note 4) T
A
= 25°C
LTC3406B (Note 4) 0°C
≤
T
A
≤
85°C
LTC3406B (Note 4) –40°C
≤
T
A
≤
85°C
V
IN
= 2.5V to 5.5V (Note 4)
LTC3406B-1.5
LTC3406B-1.8
∆V
OVL
= V
OVL
– V
FB
, LTC3406B
∆V
OVL
= V
OVL
– V
OUT
, LTC3406B-1.5/LTC3406B-1.8
V
IN
= 2.5V to 5.5V
V
IN
= 3V, V
FB
= 0.5V or V
OUT
= 90%,
Duty Cycle < 35%
●
●
ELECTRICAL CHARACTERISTICS
CONDITIONS
●
∆V
FB
V
OUT
∆V
OVL
∆V
OUT
I
PK
V
LOADREG
V
IN
I
S
Reference Voltage Line Regulation
Regulated Output Voltage
Output Overvoltage Lockout
Output Voltage Line Regulation
Peak Inductor Current
Output Voltage Load Regulation
Input Voltage Range
Input DC Bias Current
Shutdown
(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
Oscillator Frequency
R
DS(ON)
of P-Channel FET
R
DS(ON)
of N-Channel FET
SW Leakage
2
U
U
W
W W
U
W
(Note 1)
Peak SW Sink and Source Current ........................ 1.3A
Operating Temperature Range (Note 2) .. – 40°C to 85°C
Junction Temperature (Notes 3, 6) ...................... 125°C
Storage Temperature Range ................ – 65°C to 150°C
Lead Temperature (Soldering, 10 sec)................. 300°C
TOP VIEW
5 V
OUT
4 V
IN
ORDER PART
NUMBER
LTC3406BES5-1.5
LTC3406BES5-1.8
S5 PART MARKING
LTE3
LTE4
S5 PACKAGE
5-LEAD PLASTIC TSOT-23
T
JMAX
= 125°C,
θ
JA
= 250°C/ W,
θ
JC
= 90°C/ W
MIN
0.5880
0.5865
0.5850
1.455
1.746
20
2.5
0.75
TYP
0.6
0.6
0.6
0.04
1.500
1.800
50
7.8
0.04
1
0.5
MAX
±30
0.6120
0.6135
0.6150
0.4
1.545
1.854
80
13
0.4
1.25
UNITS
nA
V
V
V
%/V
V
V
mV
%
%
A
%/V
●
●
●
●
2.5
300
0.1
1.2
1.5
210
0.4
0.35
±0.01
5.5
400
1
1.8
0.5
0.45
±1
V
µA
µA
MHz
kHz
Ω
Ω
µA
3406bfa
LTC3406B
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
V
RUN
I
RUN
PARAMETER
RUN Threshold
RUN Leakage Current
CONDITIONS
●
●
ELECTRICAL CHARACTERISTICS
MIN
0.3
TYP
1
±0.01
MAX
1.5
±1
UNITS
V
µA
Note 1:
Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
Note 2:
The LTC3406BE 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: T
J
= T
A
+ (P
D
)(250°C/W)
Note 4:
The LTC3406B 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.
TYPICAL PERFOR A CE CHARACTERISTICS
(From Figure1a Except for the Resistive Divider Resistor Values)
Efficiency vs Input Voltage
100
95
90
T
A
= 25°C
I
OUT
= 100mA
I
OUT
= 600mA
EFFICIENCY (%)
EFFICIENCY (%)
85
80
75
70
65
60
55
50
2
EFFICIENCY (%)
I
OUT
= 10mA
3
5
4
INPUT VOLTAGE (V)
Efficiency vs Output Current
100
90
80
V
OUT
= 2.5V
T
A
= 25°C
VIN = 2.7V
VIN = 4.2V
REFERENCE VOLTAGE (V)
EFFICIENCY (%)
70
60
50
40
30
20
10
0.1
0.604
0.599
0.594
0.589
0.584
–50 –25
FREQUENCY (MHz)
VIN = 3.6V
1
100
10
OUTPUT CURRENT (mA)
U W
3406B G01
3406B G04
Efficiency vs Output Current
100
90
80
70
60
50
40
30
20
VIN = 4.2V
VIN = 3.6V
V
OUT
= 1.2V
T
A
= 25°C
100
VIN = 2.7V
90
80
70
60
50
40
30
20
1
100
10
OUTPUT CURRENT (mA)
1000
3406B GO2
Efficiency vs Output Current
V
OUT
= 1.5V
T
A
= 25°C
VIN = 2.7V
VIN = 3.6V
VIN = 4.2V
6
10
0.1
10
0.1
1
100
10
OUTPUT CURRENT (mA)
1000
3406B GO3
Reference Voltage vs
Temperature
0.614
V
IN
= 3.6V
0.609
1.65
1.60
1.55
1.50
1.45
1.40
1.35
50
25
75
0
TEMPERATURE (°C)
100
125
1.70
Oscillator Frequency vs
Temperature
V
IN
= 3.6V
1000
1.30
–50 –25
50
25
75
0
TEMPERATURE (°C)
100
125
3406B G05
3406B G06
3406bfa
3
LTC3406B
TYPICAL PERFOR A CE CHARACTERISTICS
(From Figure1a Except for the Resistive Divider Resistor Values)
Oscillator Frequency vs
Supply Voltage
1.8
OSCILLATOR FREQUENCY (MHz)
T
A
= 25°C
1.7
OUTPUT VOLTAGE (V)
1.6
1.5
1.4
1.3
1.2
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)
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)
360
340
320
300
280
260
240
220
200
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
4
U W
6
3406B G07
3406B G10
3406B G13
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
Dynamic Supply Current vs
Supply Voltage
400
380
340
V
OUT
= 1.8V
I
LOAD
= 0A
T
A
= 25°C
320
300
280
260
240
220
Dynamic Supply Current vs
Temperature
V
IN
= 3.6V
V
OUT
= 1.8V
I
LOAD
= 0A
2
3
5
4
SUPPLY VOLTAGE (V)
6
3406B G11
200
–50 –25
50
25
75
0
TEMPERATURE (°C)
100
125
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
MAIN
SWITCH
I
L
200mA/DIV
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
3406bfa
LTC3406B
TYPICAL PERFOR A CE CHARACTERISTICS
(From Figure 1a Except for the Resistive Divider Resistor Values)
Start-Up from Shutdown
RUN
5V/DIV
V
OUT
1V/DIV
I
L
500mA/DIV
V
IN
= 3.6V
40µs/DIV
V
OUT
= 1.8V
I
LOAD
= 600mA (LOAD: 3Ω RESISTOR)
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) (LTC3406B):
Feedback Pin. Receives the
feedback voltage from an external resistive divider across
the output.
V
OUT
(Pin 5) (LTC3406B-1.5/LTC3406B-1.8):
Output Volt-
age Feedback Pin. An internal resistive divider divides the
output voltage down for comparison to the internal refer-
ence voltage.
U W
Load Step
V
OUT
100mV/DIV
AC COUPLED
V
OUT
100mV/DIV
AC COUPLED
I
L
500mA/DIV
I
LOAD
500mA/DIV
Load Step
I
L
500mA/DIV
I
LOAD
500mA/DIV
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
Load Step
3406B G19
V
IN
= 3.6V
20µs/DIV
V
OUT
= 1.8V
I
LOAD
= 200mA TO 600mA
3406B G20
U
U
U
3406bfa
5
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