LTC3412
2.5A, 4MHz, Monolithic
Synchronous Step-Down Regulator
FEATURES
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DESCRIPTIO
High Efficiency: Up to 95%
2.5A Output Current
Low Quiescent Current: 62μA
Low R
DS(ON)
Internal Switches: 85mΩ
Programmable Frequency: 300kHz to 4MHz
No Schottky Diode Required
±2%
Output Voltage Accuracy
0.8V Reference Allows Low Output Voltage
Selectable Forced Continuous/Burst Mode Operation
with Adjustable Burst Clamp
Synchronizable Switching Frequency
Low Dropout Operation: 100% Duty Cycle
Power Good Output Voltage Monitor
Overtemperature Protection
Available in 16-Lead Thermally Enhanced TSSOP
and QFN Packages
The LTC
®
3412 is a high efficiency monolithic synchro-
nous, step-down DC/DC converter utilizing a constant
frequency, current mode architecture. It operates from an
input voltage range of 2.625V to 5.5V and provides an
adjustable regulated output voltage from 0.8V to 5V while
delivering up to 2.5A of output current. The internal
synchronous power switch with 85mΩ on-resistance
increases efficiency and eliminates the need for an exter-
nal Schottky diode. Switching frequency is set by an
external resistor or can be sychronized to an external
clock. 100% duty cycle provides low dropout operation
extending battery life in portable systems. OPTI-LOOP
®
compensation allows the transient response to be opti-
mized over a wide range of loads and output capacitors.
The LTC3412 can be configured for either Burst Mode
®
operation or forced continuous operation. Forced con-
tinuous operation reduces noise and RF interference while
Burst Mode operation provides high efficiency by reduc-
ing gate charge losses at light loads. In Burst Mode
operation, external control of the burst clamp level allows
the output voltage ripple to be adjusted according to the
requirements of the application. To further maximize
battery life, the P-channel MOSFET is turned on continu-
ously in dropout (100% duty cycle).
, LT, LTC, LTM, Burst Mode and OPTI-LOOP are registered trademarks of Linear
Technology Corporation. All other trademarks are the property of their respective owners.
APPLICATIO S
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Portable Instruments
Battery-Powered Equipment
Notebook Computers
Distributed Power Systems
Cellular Telephones
Digital Cameras
TYPICAL APPLICATIO
V
IN
2.7V TO 5.5V
SV
IN
R
T
4.7M
309k
Efficiency vs Load Current
22μF
PV
IN
PGOOD
SW
LTC3412
RUN/SS
470pF
15k
1000pF
100pF
PGND
SGND
I
TH
SYNC/MODE V
FB
110k
75k
392k
3412 F01
100
V
OUT
2.5V
2.5A
EFFICIENCY (%)
1μH
100μF
80
Burst Mode OPERATION
60
FORCED CONTINUOUS
40
20
V
IN
= 3.3V
V
OUT
= 2.5V
0.01
0.1
1
LOAD CURRENT (A)
10
3412 G01
0
0.001
Figure 1. 2.5V, 2.5A Step-Down Regulator
U
3412fb
U
U
1
LTC3412
ABSOLUTE
AXI U RATI GS
(Note 1)
Operating Temperature
Range (Note 2) ....................................... – 40°C to 85°C
Junction Temperature (Note 5) ............................. 125°C
Lead Temperature (Soldering, 10 sec)
TSSOP .............................................................. 300°C
Input Supply Voltage ...................................– 0.3V to 6V
I
TH
, RUN, V
FB
Voltages ............................... – 0.3V to V
IN
SYNC/MODE Voltages ................................ – 0.3V to V
IN
SW Voltage ................................... – 0.3V to (V
IN
+ 0.3V)
Peak SW Sink and Source Current ......................... 6.5A
PACKAGE/ORDER I FOR ATIO
TOP VIEW
SV
IN
PGOOD
I
TH
V
FB
R
T
SYNC/MODE
RUN/SS
SGND
1
2
3
4
5
6
7
8
17
16 PV
IN
15 SW
14 SW
13 PGND
12 PGND
11 SW
10 SW
9
PV
IN
SYNC/MODE
V
FB
16 15 14 13
RUN/SS 1
SGND 2
PV
IN
3
SW 4
5
SW
6
PGND
7
PGND
8
SW
17
12 PGOOD
11 SV
IN
10 PV
IN
9
SW
FE PACKAGE
16-LEAD PLASTIC TSSOP
EXPOSED PAD (PIN 17) IS SGND, MUST BE SOLDERED TO PCB
T
JMAX
= 125°C,
θ
JA
= 37.6°C/W,
θ
JC
= 10°C/W
UF PACKAGE
16-LEAD (4mm
×
4mm) PLASTIC QFN
EXPOSED PAD (PIN 17) IS SGND, MUST BE SOLDERED TO PCB
T
JMAX
= 125°C,
θ
JA
= 34°C/W,
θ
JC
= 1°C/W
ORDER PART NUMBER
LTC3412EFE
LTC3412IFE
FE PART MARKING
3412EFE
3412IFE
ORDER PART NUMBER
LTC3412EUF
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.
The
●
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
IN
= 3.3V unless otherwise specified.
SYMBOL
SV
IN
V
FB
I
FB
ΔV
FB
V
LOADREG
ΔV
PGOOD
R
PGOOD
I
Q
PARAMETER
Signal Input Voltage Range
Regulated Feedback Voltage
Voltage Feedback Leakage Current
Reference Voltage Line Regulation
Output Voltage Load Regulation
Power Good Range
Power Good Pull-Down Resistance
Input DC Bias Current
Active Current
Sleep
Shutdown
CONDITIONS
(Note 3)
V
IN
= 2.7V to 5.5V (Note 3)
Measured in Servo Loop, V
ITH
= 0.36V
Measured in Servo Loop, V
ITH
= 0.84V
●
●
●
●
ELECTRICAL CHARACTERISTICS
MIN
2.625
0.784
I
TH
R
T
(Note 4)
V
FB
= 0.78V, V
ITH
= 1V
V
FB
= 1V, V
ITH
= 0V
V
RUN
= 0V, V
MODE
= 0V
2
U
U
W
W W
U
W
TOP VIEW
UF PART MARKING
3412
TYP
0.800
0.1
0.04
0.02
– 0.02
±7.5
120
250
62
0.02
MAX
5.5
0.816
0.4
0.2
0.2
– 0.2
±9
200
330
80
1
UNITS
V
V
μA
%/V
%
%
%
Ω
μA
μA
μA
3412fb
LTC3412
The
●
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
IN
= 3.3V unless otherwise specified.
SYMBOL
f
OSC
f
SYNC
R
PFET
R
NFET
I
LIMIT
V
UVLO
I
LSW
V
RUN
I
RUN
PARAMETER
Switching Frequency
Switching Frequency Range
SYNC Capture Range
R
DS(ON)
of P-Channel FET
R
DS(ON)
of N-Channel FET
Peak Current Limit
Undervoltage Lockout Threshold
SW Leakage Current
RUN Threshold
RUN/SS Leakage Current
CONDITIONS
R
OSC
= 309kΩ
(Note 6)
(Note 6)
I
SW
= 1A (Note 7)
I
SW
= –1A (Note 7)
MIN
0.88
0.3
0.3
TYP
0.95
MAX
1.1
4
4
110
90
2.625
1
0.8
1
UNITS
MHz
MHz
MHz
mΩ
mΩ
A
V
μA
V
μA
ELECTRICAL CHARACTERISTICS
4
2.375
V
RUN
= 0V, V
IN
= 5.5V
0.5
85
65
5.4
2.500
0.1
0.65
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 LTC3412E 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 LTC3412I is guaranteed to meet
specified performance over the – 40°C to 85°C temperature range.
Note 3:
The LTC3412 is tested in a feedback loop that adjusts V
FB
to
achieve a specified error amplifier output voltage (I
TH
).
Note 4:
Dynamic supply current is higher due to the internal gate charge
being delivered at the switching frequency.
Note 5:
T
J
is calculated from the ambient temperature T
A
and power
dissipation as follows: LTC3412: T
J
= T
A
+ P
D
(37.6°C/W).
Note 6:
4MHz operation is guaranteed by design and not production tested.
Note 7:
Switch on resistance is guaranteed by design and test correlation
in the UF package and by production test in the FE package.
TYPICAL PERFOR A CE CHARACTERISTICS
Efficiency vs Load Current
100
100
90
80
Burst Mode OPERATION
80
EFFICIENCY (%)
EFFICIENCY (%)
60
FORCED CONTINUOUS
40
60
50
40
30
EFFICIENCY (%)
20
V
IN
= 3.3V
V
OUT
= 2.5V
0.01
0.1
1
LOAD CURRENT (A)
10
3412 G01
0
0.001
U W
Efficiency vs Load Current
100
90
V
IN
= 3.3V
V
IN
= 5V
80
70
60
50
40
30
V
OUT
= 2.5V
1MHz
Burst Mode OPERATION
0.01
0.1
1
LOAD CURRENT (A)
10
3412 G02
Efficiency vs Load Current
70
V
IN
= 3.3V
V
IN
= 5V
20
10
20
10
0
0.001
0
0.001
V
OUT
= 2.5V
1MHz
FORCED CONTINUOUS
0.01
0.1
1
LOAD CURRENT (A)
10
3412 G03
3412fb
3
LTC3412
TYPICAL PERFOR A CE CHARACTERISTICS
Efficiency vs Input Voltage
98
LOAD = 100mA
96
EFFICIENCY (%)
EFFICIENCY (%)
1μH
0.47μH
2.2μH
V
IN
= 3.3V
V
OUT
= 2.5V
LOAD = 1A
Burst Mode OPERATION
800 1300 1800 2300 2800 3300 3800
FREQUENCY (kHz)
3412 G05
%ΔV
OUT
/V
OUT
94
92
90
88
LOAD = 2.5A
LOAD = 1A
95
94
93
92
86
2.55
V
OUT
= 2.5V
1MHz
Burst Mode OPERATION
3.05
3.55 4.05 4.55
INPUT VOLTAGE (V)
5.05
3412 G04
Burst Mode Operation
V
OUT
100mV/DIV
V
OUT
20mV/DIV
I
L
1A/DIV
I
L
200mA/DIV
4μs/DIV
V
IN
= 3.3V, V
OUT
= 2.5V
LOAD = 50mA
3412 G07
20μs/DIV
I
L
1A/DIV
V
OUT
100mV/DIV
Start-Up, Burst Mode Operation
0.7960
V
OUT
1V/DIV
0.7955
REFERENCE VOLTAGE (V)
ON-RESISTANCE (mΩ)
V
RUN
1V/DIV
I
L
1A/DIV
1ms/DIV
V
IN
= 3.3V, V
OUT
= 2.5V
LOAD = 1Ω
4
U W
3412 G10
Efficiency vs Frequency
97
96
0.02
0.00
–0.02
–0.04
–0.06
–0.08
–0.10
–0.12
–0.14
–0.16
–0.18
Load Regulation
V
IN
= 3.3V
V
OUT
= 2.5V
91
300
0
0.5
1
1.5
LOAD CURRENT (A)
2
2.5
3412 G06
Load Step Transient Forced
Continuous
Load Step Transient Burst Mode
Operation
3412 G08
V
IN
= 3.3V, V
OUT
= 2.5V
LOAD STEP = NO LOAD TO 2.5A
20μs/DIV
V
IN
= 3.3V, V
OUT
= 2.5V
LOAD STEP = 50mA TO 2.5A
3412 G09
Reference Voltage
vs Temperature
120
V
IN
= 3.3V
100
80
60
40
20
0
15 35 55 75 95 115 120
TEMPERATURE (°C)
3412 G11
Switch On-Resistance
vs Input Voltage
0.7950
0.7945
0.7940
0.7935
0.7930
0.7925
0.7920
–45 –25 –5
PFET ON-RESISTANCE
NFET ON-RESISTANCE
2.5
3
3.5
4
INPUT VOLTAGE (V)
4.5
5
3412 G12
3412fb
LTC3412
TYPICAL PERFOR A CE CHARACTERISTICS
Switch On-Resistance
vs Temperature
120
110
100
ON-RESISTANCE (mΩ)
V
IN
= 3.3V
FREQUENCY (kHz)
90
80
70
60
50
40
30
20
–40 –20
NFET ON-RESISTANCE
LEAKAGE CURRENT (nA)
PFET ON-RESISTANCE
0
20 40 60 80
TEMPERATURE (°C)
Frequency vs Input Voltage
1050
1040
FREQUENCY (kHz)
R = 309k
1030
1020
1010
1000
990
2.5
FREQUENCY (kHz)
1004
1002
1000
998
996
994
992
DC SUPPLY CURRENT (μA)
3
3.5
4
4.5
INPUT VOLTAGE (V)
DC Supply Current vs Temperature
V
IN
= 3.3V
300
SUPPLY CURRENT (μA)
ACTIVE
MINIMUM PEAK INDUCTOR CURRENT (mA)
350
2500
2000
1500
1000
500
0
0
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9
BURST CLAMP VOLTAGE (V)
1
CURRENT LIMIT (A)
250
200
150
100
SLEEP
50
0
–40 –20
0
20 40 60 80
TEMPERATURE (°C)
U W
3412 G13
Switch Leakage vs Input Voltage
2.5
4500
4000
2.0
3500
3000
2500
2000
1500
1000
500
5
5.5
3412 G14
Frequency vs R
OSC
V
IN
= 3.3V
1.5
1.0
SYNCHRONOUS SWITCH
0.5
MAIN SWITCH
0
100 120
2.5
3
3.5
4
4.5
INPUT VOLTAGE (V)
0
50 150 250 350 450 550 650 750 850 950
R
OSC
(kΩ)
3412 G15
Switching Frequency
vs Temperature
1010
1008
1006
V
IN
= 3.3V
300
250
200
150
100
350
DC Supply Current
vs Input Voltage
ACTIVE
SLEEP
50
0
20 40 60 80
TEMPERATURE (°C)
100 120
3412 G17
5
5.5
3412 G16
990
–40 –20
2.5
3
3.5
4
4.5
INPUT VOLTAGE (V)
5
5.5
3412 G18
Minimum Peak Inductor Current
vs Burst Clamp Voltage
4000
3500
3000
V
IN
= 3.3V
Current Limit vs Input Voltage
6.8
6.6
6.4
6.2
6.0
5.8
5.6
5.4
2.75
100 120
3412 G19
3.25
4.75
4.25
3.75
INPUT VOLTAGE (V)
5.25
3412 G21
3412 G20
3412fb
5
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