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1
LTC3405A-1.5/LTC3405A-1.8
sn3405a1518 3405a1518fs
s
High Efficiency: Up to 93%
s
Very Low Quiescent Current: Only 20
A
During Operation
s
300mA Output Current at V
IN
= 3V
s
2.5V to 5.5V Input Voltage Range
s
1.5MHz Constant Frequency Operation
s
No Schottky Diode Required
s
Low Dropout Operation: 100% Duty Cycle
s
Stable with Ceramic Capacitors
s
Shutdown Mode Draws < 1
A Supply Current
s
3% Output Voltage Accuracy
s
Current Mode Operation for Excellent Line and
Load Transient Response
s
Overtemperature Protected
s
Low Profile (1mm) ThinSOT
TM
Package
The LTC
3405A-1.5/LTC3405A-1.8 are high efficiency
monolithic synchronous buck regulators using a constant
frequency, current mode architecture. Supply current
during operation is only 20
A and drops to <1
A in
shutdown. The 2.5V to 5.5V input voltage range makes the
LTC3405A-1.5/LTC3405A-1.8 ideally suited for single
Li-Ion battery-powered applications. 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-1.5/LTC3405A-1.8 are 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-1.5/LTC3405A-1.8 are available in a low profile
(1mm) ThinSOT package.
For adjustable output voltage, refer to the LTC3405A data
sheet.
s
Cellular Telephones
s
Personal Information Appliances
s
Wireless and DSL Modems
s
Digital Still Cameras
s
MP3 Players
s
Portable Instruments
Figure 1a. High Efficiency Step-Down Converter
1.5V, 1.8V, 1.5MHz, 300mA
Synchronous Step-Down
Regulators in ThinSOT
Figure 1b. Efficiency vs Load Current
, LTC and LT are registered trademarks of Linear Technology Corporation.
ThinSOT is a trademark of Linear Technology Corporation.
V
IN
C
IN
**
4.7
F
CER
V
IN
2.7V
TO 5.5V
*
**
LTC3405A-1.8
RUN
MODE
3
4.7
H*
3405A1518 F01
MURATA LQH3C4R7M34
TAIYO YUDEN JMK212BJ475MG
5
4
6
1
2
SW
V
OUT
GND
C
OUT
**
4.7
F
CER
V
OUT
1.8V
300mA
DESCRIPTIO
U
FEATURES
APPLICATIO S
U
TYPICAL APPLICATIO
U
OUTPUT CURRENT (mA)
0.1
EFFICIENCY (%)
10
1000
100
90
80
70
60
50
40
3405A1518 F01b
1
100
V
IN
= 2.7V
V
IN
= 5.5V
V
IN
= 4.2V
V
IN
= 3.6V
2
LTC3405A-1.5/LTC3405A-1.8
sn3405a1518 3405a1518fs
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
I
PK
Peak Inductor Current
V
IN
= 3V, V
OUT
= 90%, Duty Cycle < 35%
375
500
625
mA
V
OUT
Regulated Output Voltage
LTC3405A-1.5, MODE = 3.6V
q
1.455
1.500
1.545
V
LTC3405A-1.8, MODE = 3.6V
q
1.746
1.800
1.854
V
V
OVL
Output Overvoltage Lockout
V
OVL
= V
OVL
V
OUT
2.5
7.8
13
%
V
OUT
Output Voltage Line Regulation
V
IN
= 2.5V to 5.5V
q
0.04
0.4
%/V
V
LOADREG
Output Voltage Load Regulation
0.5
%
V
IN
Input Voltage Range
q
2.5
5.5
V
I
S
Input DC Bias Current
(Note 4)
Pulse Skipping Mode
V
OUT
= 90%, MODE = 3.6V, I
LOAD
= 0A
300
400
A
Burst Mode
Operation
V
OUT
= 103%, MODE = 0V, I
LOAD
= 0A
20
35
A
Shutdown
V
RUN
= 0V, V
IN
= 4.2V
0.1
1
A
f
OSC
Oscillator Frequency
V
OUT
= 100%
q
1.2
1.5
1.8
MHz
V
OUT
= 0V
170
kHz
R
PFET
R
DS(ON)
of P-Channel FET
I
SW
= 100mA
0.7
0.85
R
NFET
R
DS(ON)
of N-Channel FET
I
SW
= 100mA
0.6
0.90
I
LSW
SW Leakage
V
RUN
= 0V, V
SW
= 0V or 5V, V
IN
= 5V
0.01
1
A
V
RUN
RUN Threshold
q
0.3
1
1.5
V
I
RUN
RUN Leakage Current
q
0.01
1
A
V
MODE
MODE Threshold
q
0.3
1.5
2
V
I
MODE
MODE Leakage Current
q
0.01
1
A
LTC3405AES6-1.5
LTC3405AES6-1.8
T
JMAX
= 125
C,
JA
= 250
C/ W
ORDER PART
NUMBER
(Note 1)
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
S6 PART MARKING
Consult LTC Marketing for parts specified with wider operating temperature ranges.
The
q
denotes specifications which apply over the full operating temperature range, otherwise specifications are T
A
= 25
C.
V
IN
= 3.6V unless otherwise specified.
LTZQ
LTZP
ABSOLUTE AXI U RATI GS
W
W
W
U
PACKAGE/ORDER I FOR ATIO
U
U
W
ELECTRICAL CHARACTERISTICS
RUN 1
GND 2
SW 3
6 MODE
5 V
OUT
4 V
IN
TOP VIEW
S6 PACKAGE
6-LEAD PLASTIC SOT-23
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 LTC3405AE 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: 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.
3
LTC3405A-1.5/LTC3405A-1.8
sn3405a1518 3405a1518fs
INPUT VOLTAGE (V)
2.5
3.0
4.0
5.0
EFFICIENCY (%)
4.5
95
90
85
80
75
70
65
60
55
50
3405A1518 G02
3.5
5.5
Burst Mode OPERATION
V
OUT
= 1.8V
I
OUT
= 0.1mA
I
OUT
= 250mA
I
OUT
= 100mA
I
OUT
= 10mA
I
OUT
= 1mA
OUTPUT CURRENT (mA)
0.1
EFFICIENCY (%)
10
1000
100
90
80
70
60
50
40
30
20
10
0
3405A1518 G03
1
100
V
IN
= 3.6V
V
IN
= 4.2V
V
IN
= 3.6V
V
IN
= 4.2V
V
OUT
= 1.8V
PULSE SKIPPING MODE
Burst Mode OPERATION
OUTPUT CURRENT (mA)
0.1
EFFICIENCY (%)
10
1000
100
90
80
70
60
50
40
3405A1518 G04
1
100
V
IN
= 2.7V
V
IN
= 5.5V
V
IN
= 4.2V
V
IN
= 3.6V
V
OUT
= 1.8V
TYPICAL PERFOR A CE CHARACTERISTICS
U
W
OUTPUT CURRENT (mA)
60
EFFICIENCY (%)
80
100
50
70
90
0.1
10
100
1000
3405A1518 G05
40
1
V
IN
= 2.7V
V
IN
= 4.2V
V
OUT
= 1.5V
V
IN
= 3.6V
Efficiency vs Input Voltage
Efficiency vs Output Current
Efficiency vs Output Current
Efficiency vs Output Current
Oscillator Frequency vs
Temperature
Oscillator Frequency vs
Supply Voltage
Output Voltage vs Load Current
R
DS(ON
) vs Input Voltage
TEMPERATURE (
C)
50
FREQUENCY (MHz)
1.70
1.65
1.60
1.55
1.50
1.45
1.40
1.35
1.30
25
75
25
0
50
100
125
V
IN
= 3.6V
3405A1518
G07
SUPPLY VOLTAGE (V)
2
OSCILLATOR FREQUENCY (MHz)
1.8
1.7
1.6
1.5
1.4
1.3
1.2
3
4
5
6
3405A1518 G08
LOAD CURRENT (mA)
0
OUTPUT VOLTAGE (V)
1.834
1.824
1.814
1.804
1.794
1.784
1.774
100
200
300
400
3405A1518
G09
500
600
Burst Mode
OPERATION
PULSE SKIPPING MODE
INPUT VOLTAGE (V)
0
R
DS(0N)
(
)
2
4
5
3405A1518 G10
1
3
6
7
1.2
1.1
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
MAIN SWITCH
SYNCHRONOUS
SWITCH
(From Figure1a)
R
DS(ON)
vs Temperature
TEMPERATURE (
C)
50
R
DS(ON)
(
)
1.2
1.0
0.8
0.6
0.4
0.2
0
25
75
25
0
50
100
125
3405F G11
SYNCHRONOUS SWITCH
MAIN SWITCH
V
IN
= 2.7V
V
IN
= 3.6V
V
IN
= 4.2V
4
LTC3405A-1.5/LTC3405A-1.8
sn3405a1518 3405a1518fs
Dynamic Supply Current
vs Supply Voltage
Dynamic Supply Current
vs Temperature
Switch Leakage vs Temperature
Switch Leakage vs Input Voltage
SUPPLY VOLTAGE (V)
2
0
SUPPLY CURRENT (
A)
200
600
800
1000
4
1800
3405A1518 G12
400
3
2.5
4.5
5
3.5
5.5
1200
1400
1600
PULSE SKIPPING MODE
BURST MODE OPERATION
V
OUT
= 1.8V
I
LOAD
= 0A
TEMPERATURE (
C)
50
SWITCH LEAKAGE (nA)
160
140
120
100
80
60
40
20
0
25
75
25
0
50
100
125
V
IN
= 5.5V
RUN = 0V
3405F G14
MAIN SWITCH
SYNCHRONOUS
SWITCH
INPUT VOLTAGE (V)
0
SWITCH LEAKAGE (pA)
60
50
40
30
20
10
0
1
2
3
4
3405F G15
5
6
RUN = 0V
MAIN SWITCH
SYNCHRONOUS
SWITCH
SW
5V/DIV
V
OUT
100mV/DIV
AC COUPLED
I
L
100mA/DIV
3405A1518
G16
5
s/DIV
V
IN
= 3.6V
V
OUT
= 1.8V
I
LOAD =
20mA
SW
5V/DIV
V
OUT
10mV/DIV
AC
COUPLED
I
L
100mA/DIV
3405A1518
G17
500ns/DIV
V
IN
= 3.6V
V
OUT
= 1.8V
I
LOAD =
20mA
RUN
2V/DIV
V
OUT
1V/DIV
I
L
200mA/DIV
3405A1518
G18
100
s/DIV
V
IN
= 3.6V
V
OUT
= 1.8V
I
LOAD =
250mA
3405A1518
G19
V
OUT
100mV/DIV
AC
COUPLED
I
LOAD
200mA/DIV
I
L
200mA/DIV
40
s/DIV
V
IN
= 3.6V
V
OUT
= 1.8V
I
LOAD =
0mA TO 250mA
PULSE SKIPPING MODE
TYPICAL PERFOR A CE CHARACTERISTICS
U
W
(From Figure 1a)
Burst Mode Operation
Pulse Skipping Mode Operation
Start-Up from Shutdown
Load Step
TEMPERATURE (
C)
50
300
340
25
75
3405A1518 G13
260
25
0
50
100
125
220
180
140
100
60
20
0
SUPPLY CURRENT (
A)
V
IN
= 3.6V
V
OUT
= 1.8V
I
LOAD
= 0A
PULSE SKIPPING MODE
BURST MODE OPERATION
5
LTC3405A-1.5/LTC3405A-1.8
sn3405a1518 3405a1518fs
U
U
U
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 <1
A 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 2.2
F 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 1.2V 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.
3405A1518
G20
V
OUT
100mV/DIV
AC
COUPLED
I
LOAD
200mA/DIV
I
L
200mA/DIV
40
s/DIV
V
IN
= 3.6V
V
OUT
= 1.8V
I
LOAD =
20mA TO 250mA
PULSE SKIPPING MODE
V
OUT
100mV/DIV
AC
COUPLED
I
LOAD
200mA/DIV
I
L
200mA/DIV
3405A1518
G21
40
s/DIV
V
IN
= 3.6V
V
OUT
= 1.8V
I
LOAD =
20mA TO 250mA
Burst Mode OPERATION
3405A1518
G22
40
s/DIV
V
IN
= 3.6V
V
OUT
= 1.8V
I
LOAD =
0mA TO 250mA
Burst Mode OPERATION
V
OUT
100mV/DIV
AC
COUPLED
I
LOAD
200mA/DIV
I
L
200mA/DIV
TYPICAL PERFOR A CE CHARACTERISTICS
U
W
Load Step
Load Step
Load Step
(From Figure 1a)
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