LTC3404
1.4MHz High Efficiency
Monolithic Synchronous
Step-Down Regulator
FEATURES
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DESCRIPTIO
High Efficiency: Up to 95%
Very Low Quiescent Current: Only 10
μ
A
During Operation
600mA Output Current at V
IN
= 3.3V
2.65V to 6V Input Voltage Range
1.4MHz Constant Frequency Operation
No Schottky Diode Required
Low Dropout Operation: 100% Duty Cycle
Synchronizable from 1MHz to 1.7MHz
Selectable Burst Mode
®
Operation or
Pulse Skipping Mode
0.8V Reference Allows Low Output Voltages
Shutdown Mode Draws < 1μA Supply Current
±2%
Output Voltage Accuracy
Current Mode Control for Excellent Line and
Load Transient Response
Overcurrent and Overtemperature Protected
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 10μA and drops to < 1μA 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.
, LT, LTC and LTM 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.
APPLICATIO S
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Cellular Telephones
Wireless and DSL Modems
Personal Information Appliances
Portable Instruments
Distributed Power Systems
Battery-Powered Equipment
TYPICAL APPLICATIO
V
IN
2.65V
TO 6V
7
10μF***
CER
6
1
2
47pF
SYNC
V
IN
RUN
I
TH
GND V
FB
4
3
SW
5
Efficiency vs Output Load Current
100
95
EFFICIENCY (%)
High Efficiency Step-Down Converter
4.7μH*
20pF
V
OUT
†
3.3V
22μF**
CER
90
85
80
75
LTC3404
887k
280k
3404 TA01
*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
70
0.1
U
V
IN
= 3.6V
V
IN
= 4.2V
V
IN
= 6V
Burst Mode OPERATION
V
OUT
= 3.3V
L = 4.7μH
1
10
LOAD (mA)
100
1000
3404 TA02
U
U
3404fb
1
LTC3404
ABSOLUTE
(Note 1)
AXI U
RATI GS
PACKAGE/ORDER I FOR ATIO
TOP VIEW
RUN
I
TH
V
FB
GND
1
2
3
4
8
7
6
5
PLL LPF
SYNC/MODE
V
IN
SW
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 (DC) .......................... – 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 Temperature Range (Note 2)
LTC3404E/LTC3404I ........................... –40°C to 85°C
LTC3404MP ...................................... –55°C to 125°C
Junction Temperature (Note 3) ............................ 125°C
Storage Temperature Range ................. – 65°C to 150°C
Lead Temperature (Soldering, 10 sec).................. 300°C
MS8 PACKAGE
8-LEAD PLASTIC MSOP
T
JMAX
= 125°C,
θ
JA
= 125°C/W
ORDER PART NUMBER
LTC3404EMS8
LTC3404IMS8
LTC3404MPMS8
MS8 PART MARKING
LTKR
LTCJR
LTCXG
Order Options
Tape and Reel: Add #TR
Lead Free: Add #PBF Lead Free Tape and Reel: Add #TRPBF
Lead Free Part Marking:
http://www.linear.com/leadfree/
Consult LTC Marketing for parts specified with wider operating temperature ranges.
ELECTRICAL CHARACTERISTICS
The
●
denotes specifications which apply over –40°C to 85°C, otherwise specifications are TA = 25°C.
V
IN
= 3.6V unless otherwise specified.
SYMBOL
I
VFB
V
FB
ΔV
OVL
ΔV
FB
V
LOADREG
V
IN
I
Q
PARAMETER
Feedback Current
Regulated Output 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
SYNC Capture Range
Phase Detector Output Current
Sinking Capability
Sourcing Capability
R
DS(ON)
of P-Channel MOSFET
R
DS(ON)
of N-Channel MOSFET
Peak Inductor Current
SW Leakage
SYNC/MODE Threshold
SYNC/MODE Leakage Current
RUN Threshold
RUN Input Current
CONDITIONS
(Note 4)
(Note 4) 0°C
≤
T
A
≤
85°C
(Note 4) – 40°C
≤
T
A
≤
85°C
ΔV
OVL
= V
OVL
– V
FB
V
IN
= 2.65V to 6V (Note 4)
Measured in Servo Loop; V
ITH
= 0.9V to 1.2V
Measured in Servo Loop; V
ITH
= 1.6V to 1.2V
(Note 5)
2.65V < V
IN
< 6V, V
SYNC/MODE
= 0V, I
OUT
= 0A
V
SYNC/MODE
= V
IN
, I
OUT
= 0A
V
RUN
= 0V, V
IN
= 6V
V
FB
= 0.8V
V
FB
= 0V
MIN
●
●
●
●
●
●
0.784
0.74
20
TYP
4
0.8
0.8
50
0.05
0.1
– 0.1
2.65
400
10
0
1.4
200
MAX
30
0.816
0.84
110
0.2
0.5
– 0.5
6
700
15
1
1.65
1.7
UNITS
nA
V
V
mV
%/V
%
%
V
μA
μA
μA
MHz
kHz
MHz
μA
μA
Ω
Ω
A
μA
V
μA
V
μA
3404fb
f
OSC
f
SYNC
I
PLL LPF
●
1.25
1.0
R
PFET
R
NFET
I
PK
I
LSW
V
SYNC/MODE
I
SYNC/MODE
V
RUN
I
RUN
f
PLLIN
< f
OSC
f
PLLIN
> f
OSC
I
SW
= 100mA
I
SW
= –100mA
V
IN
= 3.3V, V
FB
= 0.7V, Duty Cycle < 35%
V
RUN
= 0V, V
SW
= 0V or 6V, V
IN
= 6V
V
SYNC/MODE
Rising
V
RUN
Rising
●
●
6
–6
0.8
●
●
0.3
0.3
20
–20
0.5
0.6
1.0
±0.01
1.0
±0.01
0.7
±0.01
40
–40
0.7
0.8
1.25
±1
1.5
±1
1.5
±1
2
U
W
U
U
W W
W
LTC3404
ELECTRICAL CHARACTERISTICS
The
●
denotes specifications which apply over –55°C to 125°C, otherwise specifications are TA = 25°C.
V
IN
= 3.6V unless otherwise specified.
SYMBOL
I
VFB
V
FB
ΔV
OVL
ΔV
FB
V
LOADREG
V
IN
I
Q
PARAMETER
Feedback Current
Regulated Output 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
SYNC Capture Range
Phase Detector Output Current
Sinking Capability
Sourcing Capability
R
DS(ON)
of P-Channel MOSFET
R
DS(ON)
of N-Channel MOSFET
Peak Inductor Current
CONDITIONS
(Note 4)
(Note 4) 0°C
≤
T
A
≤
125°C
(Note 4) – 55°C
≤
T
A
≤
125°C
ΔV
OVL
= V
OVL
– V
FB
V
IN
= 2.65V to 6V (Note 4)
Measured in Servo Loop; V
ITH
= 0.9V to 1.2V
Measured in Servo Loop; V
ITH
= 1.5V to 1.2V
(Note 5)
2.65V < V
IN
< 6V, V
SYNC/MODE
= 0V, I
OUT
= 0A
V
SYNC/MODE
= V
IN
, I
OUT
= 0A
V
RUN
= 0V, V
IN
= 6V
V
FB
= 0.8V
V
FB
= 0V
MIN
0.784
0.74
20
TYP
4
0.8
0.8
50
0.05
0.1
– 0.1
MAX
30
0.816
0.84
110
0.2
1
–1
6
700
15
1
1.65
1.7
20
–20
40
–40
0.7
0.8
1.1
1.2
±3
1.5
±1
1.5
±1
UNITS
nA
V
V
mV
%/V
%
%
V
μA
μA
μA
MHz
kHz
MHz
μA
μA
Ω
Ω
A
A
μA
V
μA
V
μA
2.65
400
10
0
1.4
200
f
OSC
f
SYNC
I
PLL LPF
1.25
1.0
R
PFET
R
NFET
I
PK
I
LSW
V
SYNC/MODE
I
SYNC/MODE
V
RUN
I
RUN
SW Leakage
SYNC/MODE Threshold
SYNC/MODE Leakage Current
RUN Threshold
RUN Input Current
f
PLLIN
< f
OSC
f
PLLIN
> f
OSC
I
SW
= 100mA
I
SW
= –100mA
V
IN
= 3.3V, V
FB
= 0.7V, Duty Cycle < 35%,
T
A
= 125°C
V
IN
= 4V, V
FB
= 0.7V, Duty Cycle < 35%,
T
A
= 125°C
V
RUN
= 0V, V
SW
= 0V or 6V, V
IN
= 6V
V
SYNC/MODE
Rising
V
RUN
Rising
6
–6
0.4
0.8
1.0
0.3
0.3
Note 1:
Stresses beyond those listed under Absolute Maximum Ratings
may cause permanent damage to the device. Exposure to any Absolute
Maximum Rating condition for extended periods may affect device
reliability and lifetime.
Note 2:
The LTC3404E is guaranteed to meet performance specifications
from 0°C to 85°C. Specifications over the – 40°C to 85°C operating
temperature range are assured by design, characterization and correlation
with statistical process controls. The LTC3404I is guaranteed to meet
performance specifications over the –40°C to 85°C operating temperature
range. The LTC3404MP is guaranteed to meet performance specifications
over the –55°C to 125°C operating temperature range.
Note 3:
T
J
is calculated from the ambient temperature T
A
and power
dissipation P
D
according to the following formulas:
T
J
= T
A
+ (P
D
)(150°C/W)
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.
3404fb
3
LTC3404
TYPICAL PERFOR A CE CHARACTERISTICS
Efficiency vs Input Voltage
95
I
OUT
= 100mA
90
I
OUT
= 10mA
85
EFFICIENCY (%)
I
OUT
= 1mA
80
75
70
EFFICIENCY (%)
EFFICIENCY (%)
I
OUT
= 300mA
I
OUT
= 0.1mA
V
OUT
= 2.5V
L = 4.7μH
3
65
Burst Mode OPERATION
60
2
6
5
INPUT VOLTAGE (V)
4
7
8
3404 G01
Efficiency vs Output Current
90
V
IN
= 3V
85
95
90
100
REFERENCE VOLTAGE (V)
EFFICIENCY (%)
EFFICIENCY (%)
80
V
IN
= 3.6V
75
70
V
IN
= 6V
65
60
0.1
V
OUT
= 1.8V
L = 4.7μH
1
10
100
OUTPUT CURRENT (mA)
1000
3404 G04
V
IN
= 4.2V
Oscillator Frequency
vs Temperature
1.55
1.50
FREQUENCY (MHz)
1.45
1.40
1.35
1.30
1.25
–50
V
IN
= 3.6V
OSCILLATOR FREQUENCY (MHz)
1.55
1.50
1.45
1.40
1.35
1.30
1.25
OUTPUT VOLTAGE (V)
–25
25
50
75
0
TEMPERATURE (°C)
4
U W
100
3404 G06
Efficiency vs Output Current
100
90
80
70
60
50
40
30
20
10
0
0.1
PULSE SKIPPING MODE
Burst Mode OPERATION
V
OUT
= 1.8V
L = 4.7μH
1
10
100
OUTPUT CURRENT (mA)
1000
3404 G02
Efficiency vs Output Current
90
85
80
75
70
65
60
55
Burst Mode OPERATION
V
IN
= 6V
V
OUT
= 2.5V
10
100
1
OUTPUT CURRENT (mA)
1000
3404 G03
V
IN
= 3.6V
V
IN
= 4.2V
L = 4.7μH
L = 3.5μH
V
IN
= 3.6V
V
IN
= 4.2V
50
0.1
Efficiency vs Output Current
0.814
V
IN
= 3.6V
Reference Voltage
vs Temperature
V
IN
= 3.6V
0.809
0.804
0.799
0.794
0.789
0.784
–50 –25
V
IN
= 6V
85
V
IN
= 4.2V
80
75
70
65
0.1
V
OUT
= 3.1V
L = 4.7μH
10
100
1
OUTPUT CURRENT (mA)
1000
3404 G4a
50
25
75
0
TEMPERATURE (°C)
100
125
3404 G05
Oscillator Frequency
vs Supply Voltage
1.83
1.82
1.81
1.80
1.79
1.78
1.77
Output Voltage vs Load Current
125
2
6
SUPPLY VOLTAGE (V)
4
8
3404
G07
PULSE SKIPPING MODE
1.76 V
IN
= 3.6V
L = 4.7μF
1.75
200
0
600
400
LOAD CURRENT (mA)
800
3404
G08
3404fb
LTC3404
TYPICAL PERFOR A CE CHARACTERISTICS
R
DS(ON)
vs Input Voltage
0.9
0.8
0.7
SYNCHRONOUS
SWITCH
1.2
1.1
1.0
0.9
DC SUPPLY CURRENT (μA)
R
DS(ON)
(Ω)
R
DS(ON)
(Ω)
0.6
0.5
0.4
0.3
0.2
0.1
0
0
1
2
5
6
4
INPUT VOLTAGE (V)
3
7
8
MAIN
SWITCH
DC Supply Current
vs Temperature
450
400
SUPPLY CURRENT (μA)
SWITCH LEAKAGE (μA)
300
V = 3.6V
250
IN
V
OUT
= 1.5V
200
150
100
50
0
–50
–25
Burst Mode
OPERATION
50
25
75
0
TEMPERATURE (°C)
100
125
SWITCH LEAKAGE (nA)
350
PULSE SKIPPING
MODE
Burst Mode Operation
SW
5V/DIV
V
OUT
50mV/DIV
AC
COUPLED
I
L
200mA/DIV
10μs/DIV
V
IN
= 4.2V
C
IN
= 10μF
V
OUT
= 1.5V C
OUT
= 22μF
L = 4.7μH
I
LOAD
= 30mA
U W
3404
G09
R
DS(ON)
vs Temperature
SYNCHRONOUS SWITCH
MAIN SWITCH
500
450
400
350
300
250
200
150
100
50
–25
0
25
50
75
TEMPERATURE (°C)
100
125
0
DC Supply Current
vs Input Voltage
V
OUT
= 1.8V
PULSE SKIPPING
MODE
0.8
0.7
0.6
0.5
0.4
0.3
–50
V
IN
= 3V
V
IN
= 5V
Burst Mode
OPERATION
2
3
4
5
6
INPUT VOLTAGE (V)
7
8
3404 G11
3404
G10
Switch Leakage vs Temperature
2.5
V
IN
= 7V
RUN = 0V
Switch Leakage vs Input Voltage
1.2
1.0
SYNCHRONOUS
SWITCH
0.8
0.6
0.4
0.2
0
0
1
2
MAIN
SWITCH
RUN = 0V
2.0
1.5
1.0
MAIN
SWITCH
SYNCHRONOUS
SWITCH
0.5
0
– 50 – 25
0
50
75
25
TEMPERATURE (°C)
100
125
6
5
4
3
INPUT VOLTAGE (V)
7
8
3404 G12
3404 G13
3404 G20
Pulse Skipping Mode Operation
Start-Up from Shutdown
SW
5V/DIV
RUN
2V/DIV
V
OUT
1V/DIV
V
OUT
10mV/DIV
I
L
100mA/DIV
I
L
500mA/DIV
3404 G14
500ns/DIV
V
IN
= 4.2V
C
IN
= 10μF
V
OUT
= 1.5V C
OUT
= 22μF
L = 4.7μH
I
LOAD
= 30mA
3404 G15
40μs/DIV
V
IN
= 3.6V
C
IN
= 10μF
V
OUT
= 1.5V C
OUT
= 22μF
L = 4.7μH
I
LOAD
= 500mA
3404 G16
3404fb
5
PCB Design
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