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LTC3404
APPLICATIO S
U
FEATURES
DESCRIPTIO
U
TYPICAL APPLICATIO
U
s
High Efficiency: Up to 95%
s
Very Low Quiescent Current: Only 10
A
During Operation
s
600mA Output Current at V
IN
= 3.3V
s
2.65V to 6V Input Voltage Range
s
1.4MHz Constant Frequency Operation
s
Synchronizable from 1MHz to 1.7MHz
s
Selectable Burst Mode
TM
Operation or
Pulse Skipping Mode
s
No Schottky Diode Required
s
Low Dropout Operation: 100% Duty Cycle
s
0.8V Reference Allows Low Output Voltages
s
Shutdown Mode Draws < 1
A Supply Current
s
2% Output Voltage Accuracy
s
Current Mode Control for Excellent Line and
Load Transient Response
s
Overcurrent and Overtemperature Protected
s
Available in 8-Lead MSOP Package
The LTC
3404 is a high efficiency monolithic synchro-
nous buck regulator using a constant frequency, current
mode architecture. Supply current during operation is
only 10
A and drops to < 1
A in shutdown. The 2.65V to
6V input voltage range makes the LTC3404 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 1.4MHz, allowing
the use of small surface mount inductors and capacitors.
For noise sensitive applications the LTC3404 can be
externally synchronized from 1MHz to 1.7MHz. Burst
Mode operation is inhibited during synchronization or
when the SYNC/MODE pin is pulled low, preventing low
frequency ripple from interfering with audio circuitry.
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 LTC3404 is available in a
space saving 8-lead MSOP package.
For higher input voltage (11V abs max) applications, refer
to the LTC1877 data sheet.
s
Cellular Telephones
s
Wireless and DSL Modems
s
Personal Information Appliances
s
Portable Instruments
s
Distributed Power Systems
s
Battery-Powered Equipment
High Efficiency Step-Down Converter
1.4MHz High Efficiency
Monolithic Synchronous
Step-Down Regulator
, LTC and LT are registered trademarks of Linear Technology Corporation.
Burst Mode is a trademark of Linear Technology Corporation.
Efficiency vs Output Load Current
LOAD (mA)
80
75
EFFICIENCY (%)
85
90
95
100
0.1
10
100
1000
3404 TA02
70
1
V
IN
= 6V
V
IN
= 4.2V
V
IN
= 3.6V
Burst Mode OPERATION
V
OUT
= 3.3V
L = 4.7
H
22
F**
CER
7
6
1
2
5
3
4
SW
V
FB
LTC3404
GND
4.7
H*
10
F***
CER
47pF
V
OUT
3.3V
*
**
***
TOKO D52LC A914BYW-4R7M
TAIYO-YUDEN CERAMIC JMK325BJ226MM
TAIYO-YUDEN CERAMIC LMK325BJ106MN
V
OUT
CONNECTED TO V
IN
FOR 2.65V < V
IN
< 3.3V
887k
20pF
280k
3404 TA01
SYNC
V
IN
RUN
I
TH
V
IN
2.65V
TO 6V
2
LTC3404
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
I
VFB
Feedback Current
(Note 4)
q
4
30
nA
V
FB
Regulated Output Voltage
(Note 4) 0
C
T
A
85
C
0.784
0.8
0.816
V
(Note 4) 40
C
T
A
85
C
q
0.74
0.8
0.84
V
V
OVL
Output Overvoltage Lockout
V
OVL
= V
OVL
V
FB
q
20
50
110
mV
V
FB
Reference Voltage Line Regulation
V
IN
= 2.65V to 6V (Note 4)
0.05
0.2
%/V
V
LOADREG
Output Voltage Load Regulation
Measured in Servo Loop; V
ITH
= 0.9V to 1.2V
q
0.1
0.5
%
Measured in Servo Loop; V
ITH
= 1.6V to 1.2V
q
0.1
0.5
%
V
IN
Input Voltage Range
q
2.65
6
V
I
Q
Input DC Bias Current
(Note 5)
Pulse Skipping Mode
2.65V < V
IN
< 6V, V
SYNC/MODE
= 0V, I
OUT
= 0A
400
700
A
Burst Mode Operation
V
SYNC/MODE
= V
IN
, I
OUT
= 0A
10
15
A
Shutdown
V
RUN
= 0V, V
IN
= 6V
0
1
A
f
OSC
Oscillator Frequency
V
FB
= 0.8V
q
1.25
1.4
1.65
MHz
V
FB
= 0V
200
kHz
f
SYNC
SYNC Capture Range
1.0
1.7
MHz
I
PLL LPF
Phase Detector Output Current
Sinking Capability
f
PLLIN
< f
OSC
q
6
20
40
A
Sourcing Capability
f
PLLIN
> f
OSC
q
6
20
40
A
R
PFET
R
DS(ON)
of P-Channel MOSFET
I
SW
= 100mA
0.5
0.7
R
NFET
R
DS(ON)
of N-Channel MOSFET
I
SW
= 100mA
0.6
0.8
LTC3404EMS8
T
JMAX
= 125
C,
JA
= 150
C/ W
ORDER PART
NUMBER
(Note 1)
Input Supply Voltage (V
IN
)........................... 0.3V to 7V
I
TH
, PLL LPF Voltage ................................ 0.3V to 2.7V
RUN, V
FB
Voltages ...................................... 0.3V to V
IN
SYNC/MODE Voltage .................................. 0.3V to V
IN
SW Voltage ................................... 0.3V to (V
IN
+ 0.3V)
P-Channel MOSFET Source Current (DC) ........... 800mA
N-Channel MOSFET Sink Current (DC) ............... 800mA
Peak SW Sink and Source Current ........................ 1.5A
Operating Ambient 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
1
2
3
4
8
7
6
5
TOP VIEW
MS8 PACKAGE
8-LEAD PLASTIC MSOP
PLL LPF
SYNC/MODE
V
IN
SW
RUN
I
TH
V
FB
GND
MS8 PART MARKING
Consult factory for parts specified with wider operating temperature ranges.
The
q
denotes specifications which apply over the full operating temperature range, otherwise specifications are TA = 25
C.
V
IN
= 3.6V unless otherwise specified.
LTKR
ABSOLUTE AXI U RATI GS
W
W
W
U
PACKAGE/ORDER I FOR ATIO
U
U
W
ELECTRICAL CHARACTERISTICS
3
LTC3404
Note 1: Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
Note 2: The LTC3404E 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 formulas:
LTC3404EMS8: T
J
= T
A
+ (P
D
)(150
C/W)
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
I
PK
Peak Inductor Current
V
IN
= 3.3V, V
FB
= 0.7V, Duty Cycle < 35%
0.8
1.0
1.25
A
I
LSW
SW Leakage
V
RUN
= 0V, V
SW
= 0V or 6V, V
IN
= 6V
0.01
1
A
V
SYNC/MODE
SYNC/MODE Threshold
V
SYNC/MODE
Rising
q
0.3
1.0
1.5
V
I
SYNC/MODE
SYNC/MODE Leakage Current
0.01
1
A
V
RUN
RUN Threshold
V
RUN
Rising
q
0.3
0.7
1.5
V
I
RUN
RUN Input Current
0.01
1
A
The
q
denotes specifications which apply over the full operating temperature range, otherwise specifications are TA = 25
C.
V
IN
= 3.6V unless otherwise specified.
Note 4: The LTC3404 is tested in a feedback loop which servos V
FB
to the
balance point for the error amplifier (V
ITH
= 1.2V).
Note 5: Dynamic supply current is higher due to the gate charge being
delivered at the switching frequency.
ELECTRICAL CHARACTERISTICS
TYPICAL PERFOR A CE CHARACTERISTICS
U
W
Efficiency vs Input Voltage
Efficiency vs Output Current
Efficiency vs Output Current
INPUT VOLTAGE (V)
2
EFFICIENCY (%)
75
80
5
7
3404 G01
70
60
85
65
3
4
6
90
95
8
Burst Mode OPERATION
V
OUT
= 2.5V
L = 4.7
H
I
OUT
= 100mA
I
OUT
= 10mA
I
OUT
= 1mA
I
OUT
= 300mA
I
OUT
= 0.1mA
OUTPUT CURRENT (mA)
30
EFFICIENCY (%)
90
100
20
10
80
50
70
60
40
0.1
10
100
1000
3404 G02
0
1
V
IN
= 3.6V
V
IN
= 3.6V
V
IN
= 4.2V
V
IN
= 4.2V
PULSE SKIPPING MODE
Burst Mode OPERATION
V
OUT
= 1.8V
L = 4.7
H
OUTPUT CURRENT (mA)
55
EFFICIENCY (%)
65
70
80
90
0.1
10
100
1000
3404 G03
1
75
60
50
85
L = 4.7
H
L = 3.5
H
Burst Mode OPERATION
V
IN
= 6V
V
OUT
= 2.5V
4
LTC3404
TYPICAL PERFOR A CE CHARACTERISTICS
U
W
Oscillator Frequency
vs Temperature
Efficiency vs Output Current
TEMPERATURE (
C)
50
REFERENCE VOLTAGE (V)
0.814
0.809
0.804
0.799
0.794
0.789
0.784
25
75
3404 G05
25
0
50
100
125
V
IN
= 3.6V
Oscillator Frequency
vs Supply Voltage
INPUT VOLTAGE (V)
1
0
R
DS(ON)
(
)
0.5
0.6
0.7
5
6
7
8
3404
G09
0.4
0.3
0
0.1
2
3
4
0.2
0.9
0.8
SYNCHRONOUS
SWITCH
MAIN
SWITCH
Reference Voltage
vs Temperature
Output Voltage vs Load Current
R
DS(ON)
vs Input Voltage
R
DS(ON)
vs Temperature
DC Supply Current
vs Input Voltage
TEMPERATURE (
C)
50
25
0.3
R
DS(ON)
(
)
0.4
0.6
0.7
0.8
75
100
1.2
3404
G10
0.5
0
25
50
125
0.9
1.0
1.1
V
IN
= 3V
V
IN
= 5V
SYNCHRONOUS SWITCH
MAIN SWITCH
OUTPUT CURRENT (mA)
75
EFFICIENCY (%)
85
95
70
80
90
0.1
10
100
1000
3404 G04
65
1
V
IN
= 3V
V
IN
= 6V
V
OUT
= 1.8V
L = 4.7
H
V
IN
= 4.2V
V
IN
= 3.6V
OUTPUT CURRENT (mA)
80
75
EFFICIENCY (%)
85
90
95
100
0.1
10
100
1000
3404 G4a
70
65
1
V
IN
= 6V
V
IN
= 3.6V
V
OUT
= 3.1V
L = 4.7
H
V
IN
= 4.2V
Efficiency vs Output Current
TEMPERATURE (
C)
50
FREQUENCY (MHz)
1.55
1.50
1.45
1.40
1.35
1.30
1.25
100
75
3404 G06
25
0
50
25
125
V
IN
= 3.6V
SUPPLY VOLTAGE (V)
OSCILLATOR FREQUENCY (MHz)
1.25
1.35
1.30
8
3404
G07
2
4
6
1.55
1.50
1.45
1.40
LOAD CURRENT (mA)
0
1.75
1.76
1.77
OUTPUT VOLTAGE (V)
1.78
1.80
1.81
1.82
200
400
3404
G08
1.79
600
800
1.83
PULSE SKIPPING MODE
V
IN
= 3.6V
L = 4.7
F
INPUT VOLTAGE (V)
0
DC SUPPLY CURRENT (
A)
200
500
2
4
5
3404 G11
100
400
300
250
150
50
450
350
3
6
7
8
V
OUT
= 1.8V
PULSE SKIPPING
MODE
Burst Mode
OPERATION
5
LTC3404
TYPICAL PERFOR A CE CHARACTERISTICS
U
W
Switch Leakage vs Temperature
TEMPERATURE (
C)
50
SWITCH LEAKAGE (
A)
25
3404 G13
2.0
1.0
25
0
50
0.5
0
2.5
1.5
75
100
125
MAIN
SWITCH
V
IN
= 7V
RUN = 0V
SYNCHRONOUS
SWITCH
Burst Mode Operation
Switch Leakage vs Input Voltage
INPUT VOLTAGE (V)
0
0
SWITCH LEAKAGE (nA)
0.2
0.4
0.6
0.8
2
4
6
8
3404 G20
1.0
1.2
1
3
5
7
SYNCHRONOUS
SWITCH
MAIN
SWITCH
RUN = 0V
Pulse Skipping Mode Operation
Start-Up from Shutdown
Load Step Response
Load Step Response
Load Step Response
DC Supply Current
vs Temperature
TEMPERATURE (
C)
50
300
350
400
450
250
200
150
100
50
0
25
75
3404 G12
25
0
50
125
100
SUPPLY CURRENT (
A)
PULSE SKIPPING
MODE
Burst Mode
OPERATION
V
IN
= 3.6V
V
OUT
= 1.5V
10
s/DIV
V
IN
= 4.2V
V
OUT
= 1.5V
L = 4.7
H
C
IN
= 10
F
C
OUT
= 22
F
I
LOAD
= 30mA
SW
5V/DIV
I
L
200mA/DIV
V
OUT
50mV/DIV
AC
COUPLED
3404 G14
500ns/DIV
V
IN
= 4.2V
V
OUT
= 1.5V
L = 4.7
H
C
IN
= 10
F
C
OUT
= 22
F
I
LOAD
= 30mA
SW
5V/DIV
I
L
100mA/DIV
V
OUT
10mV/DIV
3404 G15
40
s/DIV
V
IN
= 3.6V
V
OUT
= 1.5V
L = 4.7
H
C
IN
= 10
F
C
OUT
= 22
F
I
LOAD
= 200mA TO 500mA
PULSE SKIPPING MODE
V
OUT
100mV/DIV
I
L
500mA/DIV
I
TH
1V/DIV
3404 G17
40
s/DIV
V
IN
= 3.6V
V
OUT
= 1.5V
L = 4.7
H
C
IN
= 10
F
C
OUT
= 22
F
I
LOAD
= 50mA TO 500mA
PULSE SKIPPING MODE
V
OUT
100mV/DIV
I
L
500mA/DIV
I
TH
1V/DIV
3404 G18
40
s/DIV
V
IN
= 3.6V
V
OUT
= 1.5V
L = 4.7
H
C
IN
= 10
F
C
OUT
= 22
F
I
LOAD
= 50mA TO 500mA
Burst Mode OPERATION
V
OUT
100mV/DIV
I
L
500mA/DIV
I
TH
1V/DIV
3404 G19
40
s/DIV
V
IN
= 3.6V
V
OUT
= 1.5V
L = 4.7
H
C
IN
= 10
F
C
OUT
= 22
F
I
LOAD
= 500mA
RUN
2V/DIV
I
L
500mA/DIV
V
OUT
1V/DIV
3404 G16
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