LTC3409
600mA Low V
IN
Buck
Regulator in 3mm
×
3mm DFN
DESCRIPTIO
The LTC
®
3409 is a high efficiency, monolithic synchro-
nous buck regulator using a constant frequency, current
mode architecture. The output voltage is adjusted via an
external resistor divider.
Fixed switching frequencies of 1.7MHz and 2.6MHz are
supported. Alternatively, an internal PLL will synchronize
to an external clock in the frequency range of 1MHz to
3MHz. This range of switching frequencies allows the use
of small surface mount inductors and capacitors, includ-
ing ceramics.
Supply current during Burst Mode operation is only 65µA
dropping to <1µA in shutdown. The 1.6V to 5.5V input
voltage range makes the LTC3409 ideally suited for single
cell Li-Ion, Li-Metal and 2-cell alkaline, NiCd or NiMH
battery-powered applications. 100% duty cycle capability
provides low dropout operation, extending battery life in
portable systems. Burst Mode operation can be user-
enabled, increasing efficiency at light loads, further ex-
tending battery life.
The internal synchronous switch increases efficiency and
eliminates the need for an external Schottky diode. Inter-
nal soft-start offers controlled output voltage rise time at
start-up without the need for external components.
, LTC and LT are registered trademarks of Linear Technology Corporation.
Burst Mode is a registered 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.
FEATURES
■
■
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■
■
■
■
■
■
■
■
■
■
■
■
■
1.6V to 5.5V Input Voltage Range
Internal Soft-Start
Selectable 1.7MHz or 2.6MHz Constant Frequency
Operation
Internal Oscillator can be Synchronizable to an
External Clock, 1MHz to 3MHz Range
High Efficiency: Up to 95%
Very Low Quiescent Current: Only 65µA During
Burst Mode
®
Operation
600mA Output Current (V
IN
= 1.8V, V
OUT
= 1.2V)
750mA Peak Inductor Current
No Schottky Diode Required
Low Dropout Operation: 100% Duty Cycle
0.613V Reference Voltage
Stable with Ceramic Capacitors
Shutdown Mode Draws <1µA Supply Current
Current Mode Operation for Excellent Line and Load
Transient Response
Overtemperature Protection
Available in a Low Profile (0.75mm) 8-Lead
(3mm
×
3mm) DFN Package
APPLICATIO S
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■
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Cellular Phones
Digital Cameras
MP3 Players
TYPICAL APPLICATIO
Burst Mode Efficiency, 1.8V
OUT
100
90
2.5V
IN
, BURST
4.2V
IN
, BURST
3.6V
IN
, BURST
0
POWER LOST
3.6V
IN
, BURST
0.1
POWER LOSS (W)
High Efficiency Step-Down Converter
V
IN
1.8V TO 5.5V
LTC3409
SW
V
IN
RUN
MODE
SYNC
*SUMIDA CDRH2D18/LD
V
FB
GND
133k
255k
2.2µH*
10pF
10µF
CER
EFFICIENCY (%)
80
70
4.7µF
CER
V
OUT
1.8V
60
50
40
30
20
3409 TA01
10
0
0.1
1
10
100
LOAD CURRENT (mA)
1000
3409 TA01b
U
U
U
1.0
3409f
1
LTC3409
ABSOLUTE
(Note 1)
AXI U
RATI GS
PACKAGE/ORDER I FOR ATIO
TOP VIEW
V
FB
GND
V
IN
V
IN
1
2
3
4
9
8
7
6
5
SYNC
RUN
SW
MODE
Input Supply Voltage .................................. – 0.3V to 6V
RUN, V
FB
, MODE, SYNC Voltages . – 0.3V to (V
IN
+ 0.3V)
SW Voltage ................................... – 0.3V to (V
IN
+ 0.3V)
Operating Temperature Range (Note 2) .. – 40°C to 85°C
Junction Temperature (Note 3) ............................ 125°C
Storage Temperature Range ................ – 65°C to 125°C
ORDER PART
NUMBER
LTC3409EDD
DD PACKAGE
8-LEAD (3mm
×
3mm) PLASTIC DFN
T
JMAX
= 125°C,
θ
JA
= 43°C/ W
EXPOSED PAD (PIN 9) IS GND
MUST BE SOLDERED TO PCB
DD PART MARKING
LBNM
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
= 2.2V unless otherwise specified.
SYMBOL
V
RUN
I
RUN
V
MODE
I
MODE
V
SYNCTH
I
SYNC
V
FB
PARAMETER
RUN Threshold
RUN Leakage Current
MODE Threshold
MODE Leakage Current
SYNC Threshold
SYNC Leakage Current
Regulated Feedback Voltage
(Note 4) T
A
= 25°C
(Note 4) 0°C
≤
T
A
≤
85°C
(Note 4) –40°C
≤
T
A
≤
85°C
∆V
OVL
=
∆V
FBOVL
– V
FB
(Note 6)
(Note 4)
I
OUT
= 100mA, 1.6V < V
IN
< 5.5V
V
IN
= 2.2V, V
FB
= 0.5V or V
OUT
= 90%,
Duty Cycle < 35%
●
●
●
●
CONDITIONS
●
MIN
0.3
0.3
0.3
0.6007
0.5992
0.5977
35
TYP
0.65
0.01
0.65
0.01
0.65
0.01
0.6130
0.6130
0.6130
61
0.04
0.04
MAX
1.1
1
1.1
1
1.1
1
0.6252
0.6268
0.6283
±30
85
0.4
0.4
1.3
UNITS
V
µA
V
µA
V
µA
V
V
V
nA
mV
%/V
%/V
A
%
●
I
VFB
∆V
OVL
∆V
FB
∆V
OUT
I
PK
V
LOADREG
V
IN
I
S
Feedback Current
∆V
FBOVL
Overvoltage Lockout
Reference Voltage Line Regulation
Output Voltage Line Regulation
Peak Inductor Current
Output Voltage Load Regulation
Input Voltage Range
Input DC Bias Current
Active Mode
Sleep Mode
Shutdown
Nominal Oscillator Frequency
SYNC Threshold
Minimum SYNC Pin Frequency
Maximum SYNC Pin Frequency
Minimum SYNC Pulse Width
Soft-Start Period
RUN↑
(Note 5)
V
OUT
= 90%, I
LOAD
= 0A
V
OUT
= 103%, I
LOAD
= 0A
V
RUN
= 0V, V
IN
= 5.5V
SYNC = GND
SYNC = V
IN
When SYNC Input is Toggling (Note 7)
●
●
0.75
1
0.5
1.6
350
65
0.1
0.9
1.8
1.7
2.6
0.63
1
3
100
1
5.5
475
120
5
2.1
3.0
f
OSC
SYNC TH
SYNC f
MIN
SYNC f
MAX
SYNC PW
t
SS
2
U
V
µA
µA
µA
MHz
MHz
V
MHz
MHz
ns
ms
3409f
W
U
U
W W
W
LTC3409
ELECTRICAL CHARACTERISTICS
The
●
denotes specifications which apply over the full operating temperature range, otherwise specifications are T
A
= 25°C.
V
IN
= 2.2V unless otherwise specified.
SYMBOL
SYNC t
O
R
PFET
R
NFET
I
LSW
PARAMETER
SYNC Timeout
R
DS(ON)
of P-Channel FET
R
DS(ON)
of N-Channel FET
SW Leakage
CONDITIONS
Delay from Removal of EXT CLK Until Fixed
Frequency Operation Begins (Note 7)
I
SW
= 100mA, Wafer Level
I
SW
= 100mA, DD Package
I
SW
= 100mA, Wafer Level
I
SW
= 100mA, DD Package
V
RUN
= 0V, V
SW
= 0V or 5V, V
IN
= 5V
MIN
TYP
30
0.33
0.35
0.22
0.25
±0.1
±3
MAX
UNITS
µs
Ω
Ω
Ω
Ω
µA
Note 1:
Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
Note 2:
The LTC3409E 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:
LTC3409: T
J
= T
A
+ (P
D
)(43°C/W)
This IC includes overtemperature protection that is intended to protect the
device during momentary overload conditions. Overtemperature protection
becomes active at a junction temperature greater than the maximum
operating junction temperature. Continuous operation above the specified
maximum operating junction temperature may impair device reliability.
Note 4:
The LTC3409 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.
Note 6:
∆V
OVL
is the amount V
FB
must exceed the regulated feedback
voltage.
Note 7:
Determined by design, not production tested.
3409f
3
LTC3409
TYPICAL PERFOR A CE CHARACTERISTICS
(From Typical Application on the front page except for the resistive divider resistor values)
Efficiency/Power Lost
vs Load Current, V
OUT
= 1.8V
100
90
80
70
EFFICIENCY (%)
1
2
EFFICIENCY (%)
60
50
40
30
20
10
0
0.1
1
10
100
LOAD CURRENT (mA)
1000
3409 G01
60
50
40
30
20
10
0
1.5
I
OUT
= 0.1mA
I
OUT
= 1mA
I
OUT
= 10mA
2.5
I
OUT
= 100mA
I
OUT
= 600mA
I
OUT
= 800mA
5.5
3409 G02
EFFICIENCY (%)
3
8
10
12
4 5
6
7
11
9
1: 2.5V
IN
, BURST
2: 3.6V
IN
, BURST
3: 4.2V
IN
, BURST
4: 2.5V
IN
, PULSE SKIP
5: 3.6V
IN
, PULSE SKIP
6: 4.2V
IN
, PULSE SKIP
7: POWER LOST, 2.5V
IN
, BURST
8: POWER LOST, 2.5V
IN
, PULSE SKIP
9: POWER LOST, 3.6V
IN
, BURST
10: POWER LOST, 3.6V
IN
, PULSE SKIP
11: POWER LOST, 4.2V
IN
, BURST
12: POWER LOST, 4.2V
IN
, PULSE SKIP
Efficiency vs Load Current
V
OUT
= 2.5V
100
90
80
70
EFFICIENCY (%)
60
50
40
30
20
10
0
0.1
1
10
100
LOAD CURRENT (mA)
1000
3409 G04
BURST
2.7V
IN
4.2V
IN
3.6V
IN
3.6V
IN
2.7V
IN
4.2V
IN
PULSE SKIP
70
EFFICIENCY (%)
60
50
40
30
20
10
0
0.1
1
10
100
LOAD CURRENT (mA)
1000
3409 G05
REFERENCE VOLTAGE (V)
4
U W
Efficiency vs Input Voltage
V
OUT
= 1.2V, Burst Mode Operation
1.0
100
90
100
90
80
70
60
50
40
30
20
10
0
Efficiency vs Input Voltage
V
OUT
= 1.2V, Pulse Skip
I
OUT
= 600mA
I
OUT
= 800mA
I
OUT
= 100mA
I
OUT
= 10mA
I
OUT
= 1mA
I
OUT
= 0.1mA
0.1
POWER LOSS (mW)
80
70
0
4.5
3.5
INPUT VOLTAGE (V)
1.5
2.5
4.5
3.5
INPUT VOLTAGE (V)
5.5
3409 G03
Efficiency vs Load Current
V
OUT
= 1.2V
100
90
80
BURST
2.5V
IN
1.6V
IN
0.618
0.617
0.616
0.615
0.614
0.613
0.612
0.611
0.610
0.609
Reference Voltage
vs Temperature
3.1V
IN
3.1V
IN
2.5V
IN
1.6V
IN
PULSE SKIP
0.608
–50 –30 –10 10 30 50 70 90 110 130 150
TEMPERATURE (°C)
1011 G06
3409f
LTC3409
TYPICAL PERFOR A CE CHARACTERISTICS
(From Typical Application on the front page except for the resistive divider resistor values)
Oscillator Frequency
vs Temperature
2.70
2.60
2.50
2.40
2.30
2.20
2.10
2.00
1.90
1.80
1.70
1.60
1.50
1.40
1.30
1.20
–50
6
OSCILLATOR FREQUENCY SHIFT (%)
V
IN
= 2.7V
V
IN
= 1.6V
V
IN
= 4.2V
OSC 2.6MHz
OSCILLATOR FREQUENCY (MHz)
OUTPUT VOLTAGE (V)
V
IN
= 4.2V
OSC 1.7MHz
V
IN
= 1.6V
V
IN
= 2.7V
–25
50
25
75
0
TEMPERATURE (°C)
R
DS(ON)
vs Input Voltage
0.450
0.400
0.350
0.300
MAIN
SWITCH
MAIN SWITCH
0.50
0.45
0.40
4.2V
2.7V
1.6V
1.6V
DYNAMIC SUPPLY CURRENT, PULSE SKIP (µA)
0.250
0.200
0.150
0.100
0.050
0
1.5
2.5
4.5
3.5
INPUT VOLTAGE (V)
5.5
3409 G10
R
DS(ON)
(Ω)
R
DS(0N)
(Ω)
SYNCHRONOUS
SWITCH
Dynamic Supply Current vs
Temperature, V
IN
= 3.6V,
V
OUT
= 1.5V, 0 Load
500
450
DYNAMIC SUPLLY CURRENT (µA)
400
350
300
250
200
150
100
50
0
–50 –25
SWITCH LEAKAGE (nA)
4000
3000
MAIN SWITCH
2000
SYNCHRONOUS SWITCH
1000
0
–50 –25
SWITCH LEAKAGE (nA)
PULSE SKIP
BURST
50
25
0
75
TEMPERATURE (°C)
U W
100
3409 G07
Oscillator Frequency Shift
vs Input Voltage
1.22
f
LOW
1.7MHz
4
2
0
–2
–4
–6
–8
–10
1.5
3.5
2.5
4.5
INPUT VOLTAGE (V)
Output Voltage vs Load Current
V
IN
= 1.6V
1.21
1.2V
OUT
BURST
1.20
1.2V
OUT
PULSE
SKIP
1.19
f
HIGH
2.6MHz
125
1.18
5.5
3409 G08
0 100 200 300 400 500 600 700 800 900
LOAD CURRENT (mA)
3409 G09
R
DS(ON)
vs Input Temperature
0.55
6000
Dynamic Supply Current
vs Input Voltage
DYNAMIC SUPPLY CURRENT, BURST/SLEEP (µA)
120
BURST/SLEEP
5000
4000
3000
2000
1000
0
1.5
2
2.5
3 3.5 4 4.5 5
INPUT VOLTAGE (V)
5.5
6
PULSE
SKIP
V
OUT
= 1.5V
I
OUT
= 0
V
FB
= 0
V
OUT
= 1.5V
I
OUT
= 0
100
80
V
FB
= V
IN
60
40
20
0
0.35
0.30
0.25
0.20
0.15
2.7V
4.2V
SYNCHRONOUS SWITCH
0.10
–50 –25
50
25
75
0
TEMPERATURE (°C)
100
125
3409 G11
3409 G12
Switch Leakage vs Temperature
V
IN
= 5.5V
6000
5000
V
IN
= 5.5V
45
40
35
30
25
Switch Leakage vs Input Voltage
MAIN SWITCH
20
15
10
5
SYNCHRONOUS
SWITCH
0
2
4
INPUT VOLTAGE (V)
6
8
3409 G15
100
125
50
25
75
0
TEMPERATURE (°C)
100
125
0
3409 G13
3409 G14
3409f
5
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