LTC3405A-1.375
1.375V, 1.5MHz, 300mA
Synchronous Step-Down
Regulators in ThinSOT
FEATURES
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DESCRIPTIO
High Efficiency: Up to 90%
Very Low Quiescent Current: Only 20
µ
A
During Operation
300mA 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
Stable with Ceramic Capacitors
Shutdown Mode Draws < 1µA Supply Current
±3%
Output Voltage Accuracy
Current Mode Operation for Excellent Line and
Load Transient Response
Overtemperature Protected
Low Profile (1mm) ThinSOT
TM
Package
The LTC
®
3405A-1.375 is a high efficiency monolithic
synchronous buck regulator using a constant frequency,
current mode architecture. Supply current during opera-
tion is only 20µA and drops to <1µA in shutdown. The 2.5V
to 5.5V input voltage range makes the LTC3405A-1.375
ideally suited for single Li-Ion battery-powered applica-
tions. 100% duty cycle provides low dropout operation,
extending battery life in portable systems.
Switching frequency is internally set at 1.5MHz, allowing
the use of small surface mount inductors and capacitors.
The LTC3405A-1.375 is specifically designed to work well
with ceramic output capacitors, achieving very low output
voltage ripple and a small PCB footprint.
The internal synchronous switch increases efficiency and
eliminates the need for an external Schottky diode. The
LTC3405A-1.375 is available in a low profile (1mm)
ThinSOT package.
For other output voltages, refer to the LTC3405A and
LTC3405A-1.5/LTC3405A-1.8 data sheets.
, 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. All other trademarks are the property of their respective
owners. 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
V
IN
2.7V
TO 5.5V
C
IN
4.7µF
CER
V
IN
RUN
MODE
GND
V
OUT
SW
100
90
4.7µH
LTC3405A-1.375
C
OUT
4.7µF
CER
EFFICIENCY (%)
V
OUT
1.375V
300mA
80
70
60
50
40
30
0.1
3405A1375 F01
Figure 1a. High Efficiency Step-Down Converter
Figure 1b. Efficiency vs Load Current
3405a1375f
U
V
IN
= 2.7V
V
IN
= 3.6V
V
IN
= 4.2V
V
IN
= 5.5V
10
100
1
OUTPUT CURRENT (mA)
1000
3405A1375 F01b
U
U
1
LTC3405A-1.375
ABSOLUTE
(Note 1)
AXI U
RATI GS
PACKAGE/ORDER I FOR ATIO
TOP VIEW
RUN 1
GND 2
SW 3
6 MODE
5 V
OUT
4 V
IN
Input Supply Voltage .................................. – 0.3V to 6V
MODE, RUN, V
OUT
Voltages....................... – 0.3V to V
IN
SW Voltage .................................. – 0.3V to (V
IN
+ 0.3V)
P-Channel Switch Source Current (DC) ............. 400mA
N-Channel Switch Sink Current (DC) ................. 400mA
Peak SW Sink and Source Current .................... 630mA
Operating Temperature Range (Note 2) .. – 40°C to 85°C
Junction Temperature (Note 3) ............................ 125°C
Storage Temperature Range ................ – 65°C to 150°C
Lead Temperature (Soldering, 10 sec)................. 300°C
ORDER PART
NUMBER
LTC3405AES6-1.375
S6 PART MARKING
LTBRP
S6 PACKAGE
6-LEAD PLASTIC TSOT-23
T
JMAX
= 125°C,
θ
JA
= 250°C/ W
Consult LTC Marketing for parts specified with wider operating temperature ranges.
ELECTRICAL CHARACTERISTICS
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
PK
V
OUT
∆V
OVL
∆V
OUT
V
LOADREG
V
IN
I
S
PARAMETER
Peak Inductor Current
Regulated Output Voltage
∆Output
Overvoltage Lockout
Output Voltage Line Regulation
Output Voltage Load Regulation
Input Voltage Range
Input DC Bias Current
Pulse Skipping Mode
Burst Mode
®
Operation
Shutdown
Oscillator Frequency
R
DS(ON)
of P-Channel FET
R
DS(ON)
of N-Channel FET
SW Leakage
RUN Threshold
RUN Leakage Current
MODE Threshold
MODE Leakage Current
(Note 4)
V
OUT
= 1.238V, MODE = 3.6V, I
LOAD
= 0A
V
OUT
= 1.42V, MODE = 0V, I
LOAD
= 0A
V
RUN
= 0V, V
IN
= 4.2V
V
OUT
= 1.375V
V
OUT
= 0V
I
SW
= 100mA
I
SW
= –100mA
V
RUN
= 0V, V
SW
= 0V or 5V, V
IN
= 5V
●
●
●
●
●
●
CONDITIONS
V
IN
= 3V, V
OUT
= 1.238V, Duty Cycle < 35%
MODE = 3.6V
∆V
OVL
= V
OVL
– V
OUT
V
IN
= 2.5V to 5.5V
●
●
MIN
375
1.334
2
TYP
500
1.375
5.6
0.04
0.5
MAX
625
1.416
9.3
0.4
5.5
UNITS
mA
V
%
%/V
%
V
µA
µA
µA
MHz
kHz
Ω
Ω
µA
V
µA
V
µA
2.5
300
20
0.1
1.2
1.5
170
0.7
0.6
±0.01
0.3
0.3
1
±0.01
1.5
±0.01
400
35
1
1.8
0.85
0.90
±1
1.5
±1
2
±1
f
OSC
R
PFET
R
NFET
I
LSW
V
RUN
I
RUN
V
MODE
I
MODE
Burst Mode is a registered trademark of Linear Technology Corporation.
Note 1:
Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
Note 2:
The LTC3405A-1.375 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:
LTC3405A-1.375: 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.
3405a1375f
2
U
W
U
U
W W
W
LTC3405A-1.375
TYPICAL PERFOR A CE CHARACTERISTICS
(From Figure1a)
Efficiency vs Input Voltage
90
80
100
90
80
Burst Mode OPERATION
EFFICIENCY (%)
EFFICIENCY (%)
60
50
40
30
PULSE SKIPPING MODE
EFFICIENCY (%)
70
60
50
40
30
2.5
Burst Mode OPERATION
I
OUT
= 0.1mA
I
OUT
= 1mA
I
OUT
= 10mA
I
OUT
= 100mA
I
OUT
= 250mA
3.0
3.5
4.0
4.5
LOAD CURRENT (mA)
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
1.2
1.1
1.0
0.9
0.8
R
DS(0N)
(Ω)
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
0
1
3
2
5
4
INPUT VOLTAGE (V)
6
7
SYNCHRONOUS
SWITCH
R
DS(ON)
(Ω)
U W
5.0
T
A
= 25°C unless otherwise noted.
Efficiency vs Output Current
100
90
80
70
60
50
3.6V
4.2V
3.6V
4.2V
1
100
10
OUTPUT CURRENT (mA)
1000
Efficiency vs Output Current
70
20
10
40
30
0.1
V
IN
= 2.7V
V
IN
= 3.6V
V
IN
= 4.2V
V
IN
= 5.5V
10
100
1
OUTPUT CURRENT (mA)
1000
3405A1375 G03
5.5
0
0.1
3405A1375 G01
3405A1375 G02
Oscillator Frequency vs
Supply Voltage
1.395
Output Voltage vs Load Current
1.7
1.385
Burst Mode
OPERATION
PULSE SKIPPING MODE
1.375
1.365
1.355
1.345
2
3
4
5
SUPPLY VOLTAGE (V)
6
3405A1375 G05
3405A1375 G06
0
100
400
200
300
CURRENT LOAD (mA)
500
3405A1375 G04
R
DS(ON)
vs Temperature
1.2
V
IN
= 4.2V
1.0 V = 2.7V
IN
V
IN
= 3.6V
MAIN SWITCH
0.8
0.6
0.4
0.2
SYNCHRONOUS SWITCH
MAIN SWITCH
0
–50 –25
50
25
75
0
TEMPERATURE (°C)
100
125
3405A1375 G07
3405A1375 G08
3405a1375f
3
LTC3405A-1.375
TYPICAL PERFOR A CE CHARACTERISTICS
(From Figure 1a)
Dynamic Supply Current
vs Supply Voltage
1600
I
LOAD
= 0A
1400
SUPPLY CURRENT (µA)
SUPPLY CURRENT (µA)
1000
800
600
400
200
Burst Mode OPERATION
0
2.0
2.5
3.0
3.5
4.0
4.5
5.0
5.5
PULSE SKIPPING MODE
220
180
140
100
60
Burst Mode OPERATION
20
0
–50 –25
50
25
75
0
TEMPERATURE (°C)
100
125
SWITCH LEAKAGE (nA)
1200
SUPPLY VOLTAGE (V)
3405A1375 G09
Switch Leakage vs Input Voltage
60
RUN = 0V
50
SWITCH LEAKAGE (pA)
40
30
20
SYNCHRONOUS
SWITCH
MAIN SWITCH
10
0
0
1
2
3
4
INPUT VOLTAGE (V)
Start-Up from Shutdown
V
OUT
100mV/DIV
AC
COUPLED
RUN
2V/DIV
V
OUT
1V/DIV
I
L
200mA/DIV
V
IN
= 3.6V
I
LOAD =
200mA
40µs/DIV
3405A1375 G15
4
U W
5
6
3405A1375 G12
T
A
= 25°C unless otherwise noted.
Dynamic Supply Current
vs Temperature
340
160
Switch Leakage vs Temperature
V
IN
= 5.5V
140 RUN = 0V
V
IN
= 3.6V
300 I
LOAD
= 0A
PULSE SKIPPING MODE
260
120
100
80
60
40
20
0
–50 –25
SYNCHRONOUS
SWITCH
MAIN SWITCH
50
25
75
0
TEMPERATURE (°C)
100
125
3405A1375 G10
3405A1375 G11
Burst Mode Operation
Pulse Skipping Mode Operation
SW
5V/DIV
V
OUT
100mV/DIV
AC COUPLED
I
L
100mA/DIV
SW
5V/DIV
V
OUT
10mV/DIV
I
L
100mA/DIV
V
IN
= 3.6V
I
LOAD =
20mA
5µs/DIV
3405A1375 G13
V
IN
= 3.6V
I
LOAD =
20mA
500ns/DIV
3405A1375 G14
Load Step
I
L
200mA/DIV
I
LOAD
200mA/DIV
V
IN
= 3.6V
20µs/DIV
I
LOAD =
0mA TO 250mA
PULSE SKIPPING MODE
3405A1375 G16
3405a1375f
LTC3405A-1.375
TYPICAL PERFOR A CE CHARACTERISTICS
(From Figure 1a)
Load Step
V
OUT
100mV/DIV
AC
COUPLED
V
OUT
100mV/DIV
AC
COUPLED
I
L
200mA/DIV
I
LOAD
200mA/DIV
V
IN
= 3.6V
20µs/DIV
I
LOAD =
20mA TO 250mA
PULSE SKIPPING MODE
3405A1375 G17
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 0.9V reference voltage.
MODE (Pin 6):
Mode Select Input. To select pulse skip-
ping mode, tie to V
IN
. Grounding this pin selects Burst
Mode operation. Do not leave this pin floating.
U W
T
A
= 25°C unless otherwise noted.
Load Step
V
OUT
100mV/DIV
AC
COUPLED
Load Step
I
L
200mA/DIV
I
L
200mA/DIV
I
LOAD
200mA/DIV
V
IN
= 3.6V
20µs/DIV
I
LOAD =
20mA TO 250mA
Burst Mode OPERATION
3405A1375 G18
I
LOAD
200mA/DIV
V
IN
= 3.6V
20µs/DIV
I
LOAD =
0mA TO 250mA
Burst Mode OPERATION
3405A1375 G19
U
U
U
3405a1375f
5
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