LTC3405
1.5MHz, 300mA
Synchronous Step-Down
Regulator in ThinSOT
FEATURES
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DESCRIPTIO
High Efficiency: Up to 96%
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
0.8V Reference Allows Low Output Voltages
Shutdown Mode Draws < 1µA Supply Current
±2%
Output Voltage Accuracy
Current Mode Operation for Excellent Line and
Load Transient Response
Overtemperature Protected
Low Profile (1mm) ThinSOT
TM
Package
The LTC
®
3405 is a high efficiency monolithic synchro-
nous buck regulator 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 LTC3405 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 internal synchronous switch increases efficiency and
eliminates the need for an external Schottky diode. Low
output voltages are easily supported with the 0.8V feed-
back reference voltage. The LTC3405 is available in a low
profile (1mm) ThinSOT package.
For new designs, refer to the LTC3405A data sheet. For
fixed 1.5V and 1.8V output versions, refer to the
LTC3405A-1.5/LTC3405A-1.8 data sheet.
, LTC and LT are registered trademarks 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
V
IN
2.7V
TO 5.5V
4
C
IN
†
2.2µF
CER
V
IN
RUN
MODE
GND
2
V
FB
5
SW
3
100
95
V
IN
= 3.6V
4.7µH**
22pF
EFFICIENCY (%)
V
OUT
*
3.3V
90
85
80
75
V
IN
= 5.5V
70
65
60
0.1
V
IN
= 4.2V
LTC3405
1
6
+
C
OUT
††
33µF
887k
280k
3405 F01a
*V
OUT
CONNECTED TO V
IN
FOR 2.7V < V
IN
< 3.3V
**MURATA LQH3C4R7M34
†
TAIYO YUDEN LMK212BJ225MG
††
AVX TPSB336K006R0600
Figure 1a. High Efficiency Step-Down Converter
Figure 1b. Efficiency vs Load Current
3405fa
U
1
100
10
OUTPUT CURRENT (mA)
1000
3405 F01b
U
U
1
LTC3405
ABSOLUTE
(Note 1)
AXI U
RATI GS
PACKAGE/ORDER I FOR ATIO
TOP VIEW
RUN 1
GND 2
SW 3
6 MODE
5 V
FB
4 V
IN
Input Supply Voltage .................................. – 0.3V to 6V
MODE, RUN, V
FB
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
LTC3405ES6
S6 PART MARKING
LTXQ
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
VFB
I
PK
V
FB
∆V
OVL
∆V
FB
V
LOADREG
V
IN
I
S
PARAMETER
Feedback Current
Peak Inductor Current
Regulated Feedback Voltage
∆Output
Overvoltage Lockout
Reference 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 5)
V
FB
= 0.7V, Mode = 3.6V, I
LOAD
= 0A
V
FB
= 0.83V, Mode = 0V, I
LOAD
= 0A
V
RUN
= 0V, V
IN
= 4.2V
V
FB
= 0.8V
V
FB
= 0V
I
SW
= 100mA
I
SW
= –100mA
V
RUN
= 0V, V
SW
= 0V or 5V, V
IN
= 5V
●
●
●
●
●
●
CONDITIONS
●
MIN
375
●
●
●
TYP
500
0.8
50
0.04
0.5
MAX
±30
625
0.816
80
0.4
5.5
UNITS
nA
mA
V
mV
%/V
%
V
µA
µA
µA
MHz
kHz
Ω
Ω
µA
V
µA
V
µA
V
IN
= 3V, V
FB
= 0.7V, Duty Cycle < 35%
(Note 4)
∆V
OVL
= V
OVL
– V
FB
V
IN
= 2.5V to 5.5V (Note 4)
0.784
20
2.5
300
20
0.1
1.2
1.5
210
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 LTC3405E 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:
LTC3405: T
J
= T
A
+ (P
D
)(250°C/W)
Note 4:
The LTC3405 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.
3405fa
2
U
W
U
U
W W
W
LTC3405
TYPICAL PERFOR A CE CHARACTERISTICS
(From Figure1a Except for the Resistive Divider Resistor Values)
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
80
70
60
V
IN
= 4.2V
50
40
0.1
V
OUT
= 1.3V
1
100
10
OUTPUT CURRENT (mA)
1000
3405 G05
V
IN
= 2.7V
REFERENCE VOLTAGE (V)
EFFICIENCY (%)
0.804
0.799
0.794
0.789
0.784
–50 –25
FREQUENCY (MHz)
V
IN
= 3.6V
Oscillator Frequency vs
Supply Voltage
1.8
OSCILLATOR FREQUENCY (MHz)
1.7
OUTPUT VOLTAGE (V)
1.6
1.5
1.4
1.3
1.2
R
DS(0N)
(Ω)
2
3
4
5
SUPPLY VOLTAGE (V)
U W
3405 G02
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
3405 G03
40
0.1
V
OUT
= 1.8V
1
100
10
OUTPUT CURRENT (mA)
1000
3405 G04
Reference Voltage vs
Temperature
0.814
V
IN
= 3.6V
0.809
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
1.30
–50 –25
50
25
75
0
TEMPERATURE (°C)
100
125
3405 G06
3405 G07
Output Voltage vs Load Current
1.834
1.824
1.814
1.804
1.794
1.784
V
IN
= 3.6V
1.774
6
3405 G08
R
DS(ON
) vs Input Voltage
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
SYNCHRONOUS
SWITCH
MAIN SWITCH
Burst Mode
OPERATION
PULSE SKIPPING MODE
0
100
200
300
400
LOAD CURRENT (mA)
500
600
0
1
3
2
5
4
INPUT VOLTAGE (V)
6
7
3405 G09
3405 G10
3405fa
3
LTC3405
TYPICAL PERFOR A CE CHARACTERISTICS
(From Figure 1a Except for the Resistive Divider Resistor Values)
Dynamic Supply Current
vs Temperature
600
R
DS(ON)
vs Temperature
1.2
DYNAMIC SUPPLY CURRENT (µA)
DYNAMIC SUPPLY CURRENT (µA)
V
IN
= 4.2V
1.0 V = 2.7V
IN
0.8
V
IN
= 3.6V
R
DS(ON)
(Ω)
0.6
0.4
0.2
SYNCHRONOUS SWITCH
MAIN SWITCH
0
–50 –25
50
25
75
0
TEMPERATURE (°C)
100
125
Switch Leakage vs Temperature
160
V
IN
= 5.5V
140 RUN = 0V
SWITCH LEAKAGE (nA)
SWITCH LEAKAGE (pA)
120
100
80
60
40
20
0
–50 –25
SYNCHRONOUS
SWITCH
MAIN SWITCH
50
25
75
0
TEMPERATURE (°C)
Pulse Skipping Mode Operation
SW
5V/DIV
V
OUT
20mV/DIV
AC
COUPLED
I
L
100mA/DIV
V
IN
= 3.6V
V
OUT
= 1.8V
I
LOAD =
20mA
500ns/DIV
3405 G17
4
U W
3405 G11
Dynamic Supply Current
1600
1400
1200
1000
800
600
PULSE SKIPPING MODE
400
200
Burst Mode OPERATION
0
2
3
4
5
SUPPLY VOLTAGE (V)
6
3405 G12
V
OUT
= 1.8V
I
LOAD
= 0A
500
400
300
200
100
V
IN
= 3.6V
V
OUT
= 1.8V
I
LOAD
= 0A
PULSE SKIPPING MODE
Burst Mode OPERATION
0
–50 –25
50
25
75
0
TEMPERATURE (°C)
100
125
3405 G13
Switch Leakage vs Input Voltage
60
RUN = 0V
50
40
30
20
MAIN SWITCH
10
0
SYNCHRONOUS
SWITCH
Burst Mode Operation
SW
5V/DIV
V
OUT
50mV/DIV
AC COUPLED
I
L
100mA/DIV
100
125
0
1
2
3
4
INPUT VOLTAGE (V)
5
6
3405 G15
3405 G14
V
IN
= 3.6V
V
OUT
= 1.8V
I
LOAD =
20mA
5µs/DIV
3405 G16
Start-Up from Shutdown
V
OUT
100mV/DIV
AC
COUPLED
I
L
200mA/DIV
Load Step
RUN
2V/DIV
V
OUT
1V/DIV
I
L
200mA/DIV
I
LOAD
200mA/DIV
V
IN
= 3.6V
V
OUT
= 1.8V
I
LOAD =
250mA
100µs/DIV
3405 G18
V
IN
= 3.6V
40µs/DIV
V
OUT
= 1.8V
I
LOAD =
0mA TO 250mA
PULSE SKIPPING MODE
3405 G19
3405fa
LTC3405
TYPICAL PERFOR A CE CHARACTERISTICS
(From Figure 1a Except for the Resistive Divider Resistor Values)
Load Step
V
OUT
100mV/DIV
AC
COUPLED
I
L
200mA/DIV
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
FB
(Pin 5):
Feedback Pin. Receives the feedback voltage
from an external resistive divider across the output.
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
LOAD
200mA/DIV
I
LOAD
200mA/DIV
V
IN
= 3.6V
40µs/DIV
V
OUT
= 1.8V
I
LOAD =
20mA TO 250mA
Burst Mode OPERATION
V
IN
= 3.6V
40µs/DIV
V
OUT
= 1.8V
I
LOAD =
0mA TO 250mA
Burst Mode OPERATION
3405 G20
3405 G21
3405 G22
U
U
U
3405fa
5
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