LTC3406-1.2
1.5MHz, 600mA
Synchronous Step-Down
Regulator in ThinSOT
FEATURES
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DESCRIPTIO
High Efficiency: Up to 90%
Very Low Quiescent Current: Only 20µA
600mA Output Current at V
IN
= 3V
2.5V to 5.5V Input Voltage Range
1.5MHz Constant Frequency Operation
No Schottky Diode Required
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
®
3406-1.2 is a high efficiency monolithic syn-
chronous buck regulator using a constant frequency,
current mode architecture. Supply current during opera-
tion with only 20µA drops <1µA in shutdown. The 2.5V to
5.5V input voltage range makes the LTC3406-1.2 ideally
suited for single Li-Ion battery-powered applications. 100%
duty cycle provides low dropout operation, extending
battery life in portable systems. Automatic Burst Mode
operation further increases efficiency at light loads.
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. The
LTC3406-1.2 is available in a low profile (1mm) ThinSOT
package.
, LTC and LT are registered trademarks of Linear Technology Corporation. All other
trademarks are the property of their respective owners. ThinSOT is a trademark of Linear
Technology Corporation. Protected by U.S. Patents including 5481178, 6580258, 6304066,
6127815, 6498466, 6611131.
APPLICATIO S
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Cellular Telephones
Personal Information Appliances
Wireless and DSL Modems
Digital Still Cameras
MP3 Players
Portable Instruments
TYPICAL APPLICATIO
Efficiency and Power Loss
High Efficiency Step-Down Converter
2.2µH
V
IN
2.7V TO 5.5V
C
IN
4.7µF
CER
V
IN
SW
C
OUT
10µF
CER
340612
TA01a
100
90
EFFICIENCY
LTC3406-1.2
RUN
V
OUT
GND
EFFICIENCY (%)
V
OUT
1.2V
600mA
80
70
60
50
40
30
20
10
0
0.1
V
IN
= 2.7V
V
IN
= 3.6V
V
IN
= 4.2V
1
100
10
LOAD CURRENT (mA)
POWER LOSS
U
1
0.1
U
U
POWER LOSS (W)
0.01
0.001
0.0001
0.00001
1000
340612
TA01b
340612fa
1
LTC3406-1.2
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
OUT
Input Supply Voltage .................................. – 0.3V to 6V
RUN, V
OUT
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 (V
IN
= 3V)........ 1.3A
Operating Temperature Range (Note 2) .. – 40°C to 85°C
Junction Temperature (Notes 3, 5) ...................... 125°C
Storage Temperature Range ................ – 65°C to 150°C
Lead Temperature (Soldering, 10 sec)................. 300°C
S5 PACKAGE
5-LEAD PLASTIC TSOT-23
T
JMAX
= 125°C,
θ
JA
= 250°C/ W,
θ
JC
= 90°C/ W
ORDER PART NUMBER
S5 PART MARKING
LTC3406ES5-1.2
LTBMQ
Order Options
Tape and Reel: Add #TR
Lead Free: Add #PBF Lead Free Tape and Reel: Add #TRPBF
Lead Free Part Marking:
http://www.linear.com/leadfree/
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
V
OUT
∆V
OVL
∆V
OUT
I
PK
V
LOADREG
V
IN
I
S
PARAMETER
Regulated Output Voltage
Output Overvoltage Lockout
Output Voltage Line Regulation
Peak Inductor Current
Output Voltage Load Regulation
Input Voltage Range
Input DC Bias Current
Active Mode
Sleep Mode
Shutdown
Oscillator Frequency
R
DS(ON)
of P-Channel FET
R
DS(ON)
of N-Channel FET
SW Leakage
RUN Threshold
RUN Leakage Current
(Note 4)
V
OUT
= 1.08V, I
LOAD
= 0A
V
OUT
= 1.236V, I
LOAD
= 0A
V
RUN
= 0V, V
IN
= 5.5V
V
OUT
= 1.2V
V
OUT
= 0V
I
SW
= 100mA
I
SW
= –100mA
V
RUN
= 0V, V
SW
= 0V or 5V, V
IN
= 5V
●
●
●
●
ELECTRICAL CHARACTERISTICS
CONDITIONS
I
OUT
= 100mA
∆V
OVL
= V
OVL
– V
OUT
V
IN
= 2.5V to 5.5V
V
IN
= 3V, V
OUT
= 1.08V, Duty Cycle < 35%
●
●
MIN
1.164
2.5
0.75
2.5
TYP
1.2
6.25
0.04
1
0.5
MAX
1.236
10
0.4
1.25
5.5
UNITS
V
%
%/V
A
%
V
µA
µA
µA
MHz
kHz
Ω
Ω
µA
V
µA
300
20
0.1
1.2
1.5
210
0.4
0.35
±0.01
0.3
1
±0.01
400
35
1
1.8
0.5
0.45
±1
1.5
±1
f
OSC
R
PFET
R
NFET
I
LSW
V
RUN
I
RUN
Note 1:
Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
Note 2:
The LTC3406E-1.2 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:
LTC3406-1.2: T
J
= T
A
+ (P
D
)(250°C/W)
Note 4:
Dynamic supply current is higher due to the gate charge being
delivered at the switching frequency.
Note 5:
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.
340612fa
2
U
W
U
U
W W
W
LTC3406-1.2
TYPICAL PERFOR A CE CHARACTERISTICS
(From Figure 1)
Efficiency vs Input Voltage
100
95
EFFICIENCY (%)
100
90
REFERENCE VOLTAGE (V)
I
OUT
= 100mA
85
I
OUT
= 10mA
80
75
70
2
3
5
4
INPUT VOLTAGE (V)
6
340612 G01
EFFICIENCY (%)
90
I
OUT
= 600mA
Oscillator Frequency vs
Temperature
1.70
V
IN
= 3.6V
1.65
1.8
OSCILLATOR FREQUENCY (MHz)
1.55
1.50
1.45
1.40
1.35
1.30
–50 –25
50
25
75
0
TEMPERATURE (°C)
100
125
1.6
1.5
1.4
1.3
1.2
OUTPUT VOLTAGE (V)
1.60
FREQUENCY (MHz)
R
DS(ON)
vs Input Voltage
0.7
0.6
0.5
R
DS(ON)
(Ω)
0.4
0.3
0.2
0.1
0
0
1
5
4
2
3
INPUT VOLTAGE (V)
6
7
T
A
= 25°C
0.7
0.6
R
DS(ON)
(Ω)
MAIN
SWITCH
0.5
0.4
0.3
0.2
0.1
0
–50 –25
MAIN SWITCH
SYNCHRONOUS SWITCH
50
25
75
0
TEMPERATURE (°C)
100
125
SUPPLY CURRENT (µA)
SYNCHRONOUS
SWITCH
U W
340612
G07
T
A
= 25°C unless otherwise specified.
Reference Voltage vs
Temperature
1.228
V
IN
= 3.6V
1.218
1.208
1.198
1.188
1.178
1.168
–50 –25
Efficiency and Power Loss
80
70
60
50
40
0.1
V
IN
= 2.7V
V
IN
= 3.6V
V
IN
= 4.2V
1
10
I
LOAD
(mA)
100
1000
340612
GO2
50
25
75
0
TEMPERATURE (°C)
100
125
340612 G03
Oscillator Frequency vs
Supply Voltage
T
A
= 25°C
1.225
Output Voltage vs Load Current
1.7
1.215
1.205
1.195
1.185
1.175
2
3
4
5
SUPPLY VOLTAGE (V)
6
340612
G05
0 100 200 300 400 500 600 700 800 900 1000
LOAD CURRENT (mA)
340612
G06
340612 G04
R
DS(ON)
vs Temperature
50
Supply Current vs Supply Voltage
45
40
35
30
25
20
15
10
5
0
2
4
3
5
SUPPLY VOLTAGE (V)
6
340612 G09
V
IN
= 2.7V
V
IN
= 4.2V
V
IN
= 3.6V
I
LOAD
= 0A
340612
G08
340612fa
3
LTC3406-1.2
TYPICAL PERFOR A CE CHARACTERISTICS
(From Figure 1)
Supply Current vs Temperature
50
45
40
V
IN
= 3.6V
I
LOAD
= 0A
SWITCH LEAKAGE (nA)
300
V
IN
= 5.5V
RUN = 0V
250
200
150
100
50
0
–50 –25
MAIN SWITCH
SYNCHRONOUS SWITCH
SUPPLY CURRENT (µA)
35
30
25
20
15
10
5
0
–50 –25
50
25
0
75
TEMPERATURE (°C)
100
125
Switch Leakage vs Input Voltage
120
100
SWITCH LEAKAGE (pA)
80
60
40
20
0
RUN = 0V
T
A
= 25°C
SYNCHRONOUS
SWITCH
0
1
(From Figure 1a Except for the Resistive Divider Resistor Values)
Load Step
RUN
2V/DIV
V
OUT
1V/DIV
I
L
500mA/DIV
V
OUT
100mV/DIV
AC COUPLED
I
LOAD
500mA/DIV
I
L
500mA/DIV
V
IN
= 3.6V
I
LOAD
= 100mA TO 600mA
4
U W
Switch Leakage vs Temperature
50
25
75
0
TEMPERATURE (°C)
100
125
340612 G10
340612
G11
Discontinuous Operation
SW
2V/DIV
V
OUT
50mV/DIV
AC COUPLED
I
L
200mA/DIV
4µs/DIV
V
IN
= 3.6V
I
LOAD
= 25mA
3406B12 G13
MAIN
SWITCH
2
3
4
INPUT VOLTAGE (V)
5
6
340612 G12
Load Step
40µs/DIV
340612 G14
20µs/DIV
V
IN
= 3.6V
I
LOAD
= 25mA TO 600mA
340612 G15
340612fa
LTC3406-1.2
TYPICAL PERFOR A CE CHARACTERISTICS
(From Figure 1a Except for the Resistive Divider Resistor Values)
Load Step
V
OUT
100mV/DIV
AC COUPLED
I
LOAD
500mA/DIV
I
L
500mA/DIV
V
OUT
100mV/DIV
AC COUPLED
I
LOAD
500mA/DIV
I
L
500mA/DIV
V
IN
= 3.6V
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
OUT
(Pin 5):
Output Voltage Feedback Pin. An internal
resistive divider divides the output voltage down for com-
parison to the internal reference voltage.
FU CTIO AL DIAGRA
OSC
OSC
FREQ
SHIFT
V
OUT
5
60k
FB
120k
0.8V
V
IN
RUN
1
0.8V REF
0.8V +
∆V
OVL
SHUTDOWN
–
I
RCMP
+
W
–
+
OVDET
–
+
U W
Load Step
20µs/DIV
340612 G16
20µs/DIV
V
IN
= 3.6V
I
LOAD
= 200mA TO 600mA
340612 G17
U
U
U
U
U
SLOPE
COMP
0.65V
4 V
IN
–
+
–
EA
S
R
Q
Q
SWITCHING
LOGIC
AND
BLANKING
CIRCUIT
I
COMP
+
5Ω
RS LATCH
OV
ANTI-
SHOOT-
THRU
3 SW
2 GND
3406B12 BD
340612fa
5
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