LTC3405A-1.5/LTC3405A-1.8
1.5V, 1.8V, 1.5MHz, 300mA
Synchronous Step-Down
Regulators in ThinSOT
FEATURES
s
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DESCRIPTIO
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s
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High Efficiency: Up to 93%
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-1.5/LTC3405A-1.8 are high efficiency
monolithic synchronous buck regulators using a constant
frequency, current mode architecture. Supply current
during operation is only 20µA and drops to <1µA 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.
, LTC and LT are registered trademarks of Linear Technology Corporation.
ThinSOT is a trademark of Linear Technology Corporation.
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
4
C
IN
**
4.7µF
CER
V
IN
RUN
MODE
V
OUT
2
5
SW
3
100
V
IN
= 2.7V
90
4.7µH*
EFFICIENCY (%)
LTC3405A-1.8
1
6
V
OUT
1.8V
300mA
C
OUT
**
4.7µF
CER
80
70
60
50
40
0.1
V
IN
= 5.5V
GND
3405A1518 F01
*MURATA LQH3C4R7M34
**TAIYO YUDEN JMK212BJ475MG
Figure 1a. High Efficiency Step-Down Converter
Figure 1b. Efficiency vs Load Current
sn3405a1518 3405a1518fs
U
V
IN
= 3.6V
V
IN
= 4.2V
1
100
10
OUTPUT CURRENT (mA)
1000
3405A1518 F01b
U
U
1
LTC3405A-1.5/LTC3405A-1.8
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
LTC3405AES6-1.5
LTC3405AES6-1.8
S6 PART MARKING
LTZQ
LTZP
S6 PACKAGE
6-LEAD PLASTIC SOT-23
T
JMAX
= 125°C,
θ
JA
= 250°C/ W
Consult LTC Marketing for parts specified with wider operating temperature ranges.
ELECTRICAL CHARACTERISTICS
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.
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
= 90%, MODE = 3.6V, I
LOAD
= 0A
V
OUT
= 103%, MODE = 0V, I
LOAD
= 0A
V
RUN
= 0V, V
IN
= 4.2V
V
OUT
= 100%
V
OUT
= 0V
I
SW
= 100mA
I
SW
= –100mA
V
RUN
= 0V, V
SW
= 0V or 5V, V
IN
= 5V
q
q
q
q
q
q
CONDITIONS
V
IN
= 3V, V
OUT
= 90%, Duty Cycle < 35%
LTC3405A-1.5, MODE = 3.6V
LTC3405A-1.8, MODE = 3.6V
∆V
OVL
= V
OVL
– V
OUT
V
IN
= 2.5V to 5.5V
q
q
q
MIN
375
1.455
1.746
2.5
TYP
500
1.500
1.800
7.8
0.04
0.5
MAX
625
1.545
1.854
13
0.4
5.5
UNITS
mA
V
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 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.
sn3405a1518 3405a1518fs
2
U
W
U
U
W W
W
LTC3405A-1.5/LTC3405A-1.8
TYPICAL PERFOR A CE CHARACTERISTICS
(From Figure1a)
Efficiency vs Input Voltage
95
90
85
EFFICIENCY (%)
I
OUT
= 100mA
I
OUT
= 250mA
I
OUT
= 10mA
I
OUT
= 1mA
EFFICIENCY (%)
75
70
65
60
55
50
Burst Mode OPERATION
V
OUT
= 1.8V
2.5
3.0
3.5
4.0
4.5
INPUT VOLTAGE (V)
5.0
5.5
I
OUT
= 0.1mA
60
50
40
30
20
10
0
0.1
EFFICIENCY (%)
80
Efficiency vs Output Current
100
90
V
OUT
= 1.5V
V
IN
= 2.7V
V
IN
= 3.6V
1.60
OSCILLATOR FREQUENCY (MHz)
FREQUENCY (MHz)
EFFICIENCY (%)
80
V
IN
= 4.2V
70
60
50
40
0.1
10
100
1
OUTPUT CURRENT (mA)
Output Voltage vs Load Current
1.834
1.824
OUTPUT VOLTAGE (V)
1.814
1.804
1.794
R
DS(0N)
(Ω)
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
SYNCHRONOUS
SWITCH
R
DS(ON)
(Ω)
Burst Mode
OPERATION
PULSE SKIPPING MODE
1.784
1.774
0
100
200
300
400
LOAD CURRENT (mA)
U W
3405A1518 G02
3405A1518 G05
Efficiency vs Output Current
100
90 V = 3.6V
IN
80
70
V
IN
= 3.6V
V
IN
= 4.2V
V
IN
= 4.2V
80
70
60
50
100
Efficiency vs Output Current
V
IN
= 2.7V
90
V
IN
= 3.6V
V
IN
= 4.2V
V
IN
= 5.5V
PULSE SKIPPING MODE
Burst Mode OPERATION
V
OUT
= 1.8V
1
100
10
OUTPUT CURRENT (mA)
1000
40
0.1
V
OUT
= 1.8V
1
100
10
OUTPUT CURRENT (mA)
1000
3405A1518 G03
3405A1518 G04
Oscillator Frequency vs
Temperature
1.70
V
IN
= 3.6V
1.65
1.7
1.6
1.5
1.4
1.3
1.2
1.8
Oscillator Frequency vs
Supply Voltage
1.55
1.50
1.45
1.40
1.35
1.30
–50 –25
50
25
75
0
TEMPERATURE (°C)
100
125
1000
2
3
4
5
SUPPLY VOLTAGE (V)
6
3405A1518 G08
3405A1518
G07
R
DS(ON
) vs Input Voltage
1.2
1.1
1.0
0.9
0.8
MAIN SWITCH
R
DS(ON)
vs Temperature
1.2
V
IN
= 4.2V
1.0 V = 2.7V
IN
0.8
0.6
0.4
0.2
SYNCHRONOUS SWITCH
MAIN SWITCH
0
–50 –25
V
IN
= 3.6V
500
600
0
1
3
2
5
4
INPUT VOLTAGE (V)
6
7
50
25
75
0
TEMPERATURE (°C)
100
125
3405A1518
G09
3405A1518 G10
3405F G11
sn3405a1518 3405a1518fs
3
LTC3405A-1.5/LTC3405A-1.8
TYPICAL PERFOR A CE CHARACTERISTICS
(From Figure 1a)
Dynamic Supply Current
vs Supply Voltage
1800
1600
SUPPLY CURRENT (µA)
1400
1200
1000
800
600
400
200
BURST MODE OPERATION
0
2
2.5
3
3.5
4.5
4
SUPPLY VOLTAGE (V)
5
5.5
PULSE SKIPPING MODE
V
OUT
= 1.8V
I
LOAD
= 0A
340
SUPPLY CURRENT (µA)
220
180
140
100
60
BURST MODE OPERATION
20
0
–50 –25
50
25
75
0
TEMPERATURE (°C)
100
125
SWITCH LEAKAGE (nA)
Switch Leakage vs Input Voltage
60
RUN = 0V
50
SYNCHRONOUS
SWITCH
SW
5V/DIV
V
OUT
100mV/DIV
AC COUPLED
SWITCH LEAKAGE (pA)
40
30
20
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
V
OUT
= 1.8V
I
LOAD =
250mA
4
U W
3405A1518 G12
Dynamic Supply Current
vs Temperature
160
V
IN
= 3.6V
V
OUT
= 1.8V
300
I
LOAD
= 0A
260
Switch Leakage vs Temperature
V
IN
= 5.5V
RUN = 0V
140
PULSE SKIPPING MODE
120
100
80
60
40
20
0
–50 –25
SYNCHRONOUS
SWITCH
MAIN SWITCH
50
25
75
0
TEMPERATURE (°C)
100
125
3405A1518 G13
3405F G14
Burst Mode Operation
SW
5V/DIV
Pulse Skipping Mode Operation
V
OUT
10mV/DIV
AC
COUPLED
I
L
100mA/DIV
I
L
100mA/DIV
5
6
3405F G15
V
IN
= 3.6V
V
OUT
= 1.8V
I
LOAD =
20mA
5µs/DIV
3405A1518
G16
V
IN
= 3.6V
V
OUT
= 1.8V
I
LOAD =
20mA
500ns/DIV
3405A1518
G17
Load Step
I
L
200mA/DIV
I
LOAD
200mA/DIV
100µs/DIV
3405A1518
G18
V
IN
= 3.6V
40µs/DIV
V
OUT
= 1.8V
I
LOAD =
0mA TO 250mA
PULSE SKIPPING MODE
3405A1518
G19
sn3405a1518 3405a1518fs
LTC3405A-1.5/LTC3405A-1.8
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
40µs/DIV
V
OUT
= 1.8V
I
LOAD =
20mA TO 250mA
PULSE SKIPPING MODE
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 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.
U W
Load Step
V
OUT
100mV/DIV
AC
COUPLED
Load Step
I
L
200mA/DIV
I
L
200mA/DIV
I
LOAD
200mA/DIV
I
LOAD
200mA/DIV
3405A1518
G20
V
IN
= 3.6V
40µs/DIV
V
OUT
= 1.8V
I
LOAD =
20mA TO 250mA
Burst Mode OPERATION
3405A1518
G21
V
IN
= 3.6V
40µs/DIV
V
OUT
= 1.8V
I
LOAD =
0mA TO 250mA
Burst Mode OPERATION
3405A1518
G22
U
U
U
sn3405a1518 3405a1518fs
5
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