LTC3412A
3A, 4MHz, Monolithic
Synchronous Step-Down Regulator
FEATURES
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DESCRIPTIO
High Efficiency: Up to 95%
3A Output Current
Low Quiescent Current: 64μA
Low R
DS(ON)
Internal Switch: 77mΩ
2.25V to 5.5V Input Voltage Range
Programmable Frequency: 300KHz to 4MHz
±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 Protected
Available in 16-Lead Exposed Pad TSSOP and QFN
Packages
The LTC
®
3412A 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 2.25V to 5.5V and provides a
regulated output voltage from 0.8V to 5V while delivering
up to 3A of output current. The internal synchronous
power switch with 77mΩ on-resistance increases effi-
ciency and eliminates the need for an external Schottky
diode. Switching frequency is set by an external resistor or
can be synchronized 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 optimized over a wide range of
loads and output capacitors.
The LTC3412A can be configured for either Burst Mode
operation or forced continuous operation. Forced continu-
ous 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
application requirements.
, LT, LTC and LTM are registered trademarks of Linear Technology Corporation.
Burst Mode and OPTI-LOOP are registered trademarks 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, 6724174.
APPLICATIO S
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Point-of-Load Regulation
Notebook Computers
Portable Instruments
Distributed Power Systems
TYPICAL APPLICATIO
22μF
V
IN
3.3V
PV
IN
SV
IN
2.2M
294k
RT
Efficiency and Power Loss
100
95
EFFICIENCY
10000
100000
PGOOD
LTC3412A
SW
0.47μH
90
EFFICIENCY (%)
V
OUT
2.5V AT 3A
C
OUT
100μF
×2
85
80
75
70
65
60
POWER LOSS
10
100
1000
RUN/SS
1000pF
12.1k
I
TH
SYNC/MODE
820pF
PGND
SGND
V
FB
69.8k
115k
392k
3412A F01a
55
50
0.01
0.1
1
LOAD CURRENT (A)
1
10
!" ) . >
Figure 1. 2.5V/3A Step-Down Regulator
U
POWER LOSS (mW)
U
U
3412afb
1
LTC3412A
ABSOLUTE
(Note 1)
AXI U RATI GS
Operating Ambient Temperature Range
(Note 2) .............................................. – 40°C to 85°C
Junction Temperature (Note 5) ............................. 125°C
Lead Temperature (Soldering, 10 sec).................. 300°C
Input Supply Voltage ................................... –0.3V to 6V
I
TH
, RUN/SS, V
FB
, PGOOD,
SYNC/MODE Voltages .................................. –0.3 to V
IN
SW Voltages ................................. –0.3V to (V
IN
+ 0.3V)
PI CO FIGURATIO
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
V
FB
15 SW
14 SW
13 PGND
12 PGND
11 SW
10 SW
9
PV
IN
16 15 14 13
RUN/SS 1
SGND 2
PV
IN
3
SW 4
5
SW
I
TH
16 PV
IN
SYNC/MODE
R
T
PGND
PGND
FE PACKAGE
16-LEAD PLASTIC TSSOP
EXPOSED PAD IS SGND (PIN 17) MUST BE SOLDERED TO PCB
T
JMAX
= 125°C,
θ
JA
= 38°C/W,
θ
JC
= 10°C/W
UF PACKAGE
16-LEAD (4mm
×
4mm) PLASTIC QFN
T
JMAX
= 125°C,
θ
JA
= 34°C/W,
θ
JC
= 1°C/W
EXPOSED PAD (PIN 17) IS GND, MUST BE CONNECTED TO PCB
ORDER I FOR ATIO
LEAD FREE FINISH
LT3412AEFE#PBF
LT3412AIFE#PBF
LT3412AEUF#PBF
LEAD BASED FINISH
LT3412AEFE
LT3412AIFE
LT3412AEUF
TAPE AND REEL
LT3412AEFE#TRPBF
LT3412AIFE#TRPBF
LT3412AEUF#TRPBF
TAPE AND REEL
LT3412AEFE#TR
LT3412AIFE#TR
LT3412AEUF#TR
PART MARKING
3412AEFE
3412AIFE
3412A
PART MARKING
3412AEFE
3412AIFE
3412A
PACKAGE DESCRIPTION
16-Lead Plastic TSSOP
16-Lead Plastic TSSOP
16-Lead (4mm x 4mm) Plastic QFN
PACKAGE DESCRIPTION
16-Lead Plastic TSSOP
16-Lead Plastic TSSOP
16-Lead (4mm x 4mm) Plastic QFN
SW
Consult LTC Marketing for parts specified with wider operating temperature ranges.
For more information on lead free part marking, go to:
http://www.linear.com/leadfree/
For more information on tape and reel specifications, go to:
http://www.linear.com/tapeandreel/
2
U
U
W W
U
W
W
U
U
U
TOP VIEW
12 PGOOD
17
11 SV
IN
10 PV
IN
9
6
7
8
SW
TEMPERATURE RANGE
–40°C to 85°C
–40°C to 125°C
–40°C to 85°C
TEMPERATURE RANGE
–40°C to 85°C
–40°C to 125°C
–40°C to 85°C
3412afb
LTC3412A
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
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
(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
2.25
0.784
TYP
0.800
0.1
0.04
0.02
– 0.02
±7.5
120
250
64
0.02
1
MAX
5.5
0.816
0.2
0.2
0.2
– 0.2
±9
200
330
80
1
1.1
4
4
110
90
2.25
1
0.8
1
UNITS
V
V
μA
%/V
%
%
%
Ω
μA
μA
μA
MHz
MHz
MHz
mΩ
mΩ
A
V
μA
V
μA
f
OSC
f
SYNC
R
PFET
R
NFET
I
LIMIT
V
UVLO
I
LSW
V
RUN
I
RUN
(Note 4)
V
FB
= 0.78V, V
ITH
= 1V
V
FB
= 1V, V
ITH
= 0V
V
RUN
= 0V, V
MODE
= 0V
R
OSC
= 294kΩ
(Note 6)
(Note 6)
I
SW
= 1A (Note 7)
I
SW
= –1A (Note 7)
0.88
0.3
0.3
4.5
1.75
V
RUN
= 0V, V
IN
= 5.5V
0.5
77
65
6
2
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 LTC3412AE 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 full – 40°C to 85°C operating temperature
range.
Note 3:
The LTC3412A 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: LTC3412AFE: T
J
= T
A
+ P
D
(38°C/W)
LTC3412AEUF: T
J
= T
A
+ P
D
(34°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 condition in
the UF package and by final test correlation in the FE package.
3412afb
3
LTC3412A
TYPICAL PERFOR A CE CHARACTERISTICS
Efficiency vs Load Current
100
90
Burst Mode
OPERATION
80
EFFICIENCY (%)
EFFICIENCY (%)
70
60
50
40
30
20
10
0
0.01
V
IN
= 3.3V
V
OUT
= 2.5V
FIGURE 4 CIRCUIT
0.1
1
LOAD CURRENT (A)
10
3412A GO1
80
75
70
65
60
55
50
0.01
V
OUT
= 2.5V
FIGURE 4 CIRCUIT
0.1
1
LOAD CURRENT (A)
10
3412A GO2
EFFICIENCY (%)
FORCED
CONTINUOUS
Efficiency vs Input Voltage
94
92
1A
90
EFFICIENCY (%)
FIGURE 4 CIRCUIT
0.1A
88
86
84
3A
82
80
2.5
EFFICIENCY (%)
93
92
91
90
89
88
0.47μH
ΔV
OUT
/V
OUT
(%)
3.0
4.0
INPUT VOLTAGE (V)
3.5
Burst Mode Operation
V
OUT
20mV/DIV
INDUCTOR
CURRENT
1A/DIV
FIGURE 4 CIRCUIT 5μs/DIV
3412A GO7
4
U W
4.5
3412A GO4
Efficiency vs Load Current, Burst
Mode Operation
100
95
90
85
V
IN
= 5V
V
IN
= 3.3V
100
90
80
70
60
50
40
30
20
10
Efficiency vs Load Current,
Forced Continuous Operation
V
IN
= 3.3V
V
IN
= 5V
V
OUT
= 2.5V
FIGURE 4 CIRCUIT
0.1
1
LOAD CURRENT (A)
10
3412A GO3
0
0.01
Efficiency vs Frequency
96
95
94
1μH
0.22μH
–0.2
–0.3
–0.4
–0.5
–0.6
0
0.5 1.0
1.5 2.0 2.5 3.0
FREQUENCY (MHz)
3.5
4.0
FIGURE 4 CIRCUIT
V
IN
= 3.3V
0
–0.1
Load Regulation
FIGURE 4 CIRCUIT
V
IN
= 3.3V
5.0
87
0
0.5
1.0
1.5
2.0
LOAD CURRENT (A)
2.5
3.0
3412A GO5
3412A GO6
Output Voltage Ripple
Load Step Transient Burst Mode
Operation
BURST
MODE
20mV/DIV
PULSE
SKIPPING
20mV/DIV
FORCED
CONTINUOUS
20mV/DIV
V
OUT
100mV/DIV
INDUCTOR
CURRENT
2A/DIV
V
IN
= 3.3V
5μs/DIV
V
OUT
= 2.5V
FIGURE 4 CIRCUIT
3412A GO8
V
IN
= 3.3V
40μs/DIV
V
OUT
= 2.5V
F = 1MHz
LOAD STEP = 50mA TO 2A
FIGURE 4 CIRCUIT
3412A GO9
3412afb
LTC3412A
TYPICAL PERFOR A CE CHARACTERISTICS
Load Step Transient Forced
Continuous
V
OUT
2V/DIV
V
OUT
100mV/DIV
V
REF
(V)
INDUCTOR
CURRENT
2A/DIV
40μs/DIV
V
IN
= 3.3V
V
OUT
=2.5V
F = 1MHz
LOAD STEP = 0A TO 3A
FIGURE 4 CIRCUIT
Switch On-Resistance vs
Input Voltage
100
95
90
ON-RESISTANCE (mΩ)
ON-RESISTANCE (mΩ)
85
80
75
70
65
60
55
50
2.5
3.0
4.0
4.5
3.5
INPUT VOLTAGE (V)
5.0
3412A G13
100
80
60
NFET
40
20
0
–40 – 20
SWITCH LEAKAGE CURRENT (nA)
PFET
NFET
Frequency vs R
OSC
5000
4500
4000
FREQUENCY (kHz)
FREQUENCY (kHz)
V
IN
= 3.3V
1050
1040
1030
1020
1010
1000
1060
3000
2500
2000
1500
1000
500
0
40 140 240 340 440 540 640 740 840 940
R
OSC
(kΩ)
3412A G16
FREQUENCY (kHz)
3500
U W
Start-Up Transient
0.7975
0.7970
0.7965
0.7960
RUN/SS
2V/DIV
INDUCTOR
CURRENT
2A/DIV
0.7955
0.7950
0.7945
0.7940
0.7935
1ms/DIV
V
IN
= 3.3V
V
OUT
=2.5V
LOAD STEP = 2A
FIGURE 4 CIRCUIT
V
REF
vs Temperature
V
IN
= 3.3V
0.7930
–45 –25
3412A G11
–5
15 35 55 75
TEMPERATURE (°C)
95
115
3412A G12
3412A G10
Switch On-Resistance vs
Temperature
120
V
IN
= 3.3V
50
45
40
35
30
25
20
15
10
5
0
0
20 40 60 80
TEMPERATURE (°C)
100 120
3412A G14
Switch Leakage Current vs
Input Voltage
PFET
PFET
NFET
2.5
3.0
4.0
4.5
3.5
INPUT VOLTAGE (V)
5.0
5.5
3412A G15
Frequency vs Input Voltage
1020
R
OSC
= 294k
Frequency vs Temperature
V
IN
= 3.3V
1015 R
OSC
= 294k
1010
1005
1000
995
990
985
980
975
990
2.5
3.0
4.0
4.5
3.5
INPUT VOLTAGE (V)
5.0
5.5
970
–40 –20
0
20 40 60 80
TEMPERATURE (°C)
100 120
3412A G18
3412A G17
3412afb
5
测试/测量
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