FeaTures
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LTC3418
8A, 4MHz, Monolithic
Synchronous Step-Down
Regulator
DescripTion
The
LTC
®
3418
is a high efficiency, monolithic synchronous
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 8A of output
current. The internal synchronous power switch increases
efficiency 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. OPTI-LOOP
®
compensation allows the transient response to be optimized
over a wide range of loads and output capacitors.
The LTC3418 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
reducing 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. A tracking input in the
LTC3418 allows for proper sequencing with respect to
another power supply.
L,
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.
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High Efficiency: Up to 95%
8A Output Current
2.25V to 5.5V Input Voltage Range
Low R
DS(ON)
Internal Switch: 35mΩ
Tracking Input to Provide Easy Supply Sequencing
Programmable Frequency: 300kHz to 4MHz
0.8V ±1% Reference Allows Low Output Voltage
Quiescent Current: 380µA
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
38-Lead Low Profile (0.75mm) Thermally Enhanced
QFN (5mm
×
7mm) Package
applicaTions
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Microprocessor, DSP and Memory Supplies
Distributed 2.5V, 3.3V and 5V Power Systems
Automotive Applications
Point of Load Regulation
Notebook Computers
Typical applicaTion
2.5V/8A Step-Down Regulator
V
IN
2.8V TO 5.5V
SV
IN
TRACK PV
IN
R
T
2.2M
30.1k
SW
LTC3418
PGOOD
PGND
RUN/SS
SGND
I
TH
SYNC/MODE V
FB
332
1.69k
4.32k
3418 TA01a
Efficiency and Power Loss vs Load Current
100
100000
EFFICIENCY
90
C
IN
47µF
×4
0.2µH
C
OUT
100µF
×2
EFFICIENCY (%)
V
OUT
2.5V
8A
80
70
60
50
40
30
20
0.01
0.1
1
LOAD CURRENT (A)
V
IN
= 3.3V
V
OUT
= 2.5V
10
3418 TA01b
10000
POWER LOSS (mW)
1000
POWER LOSS
1000pF
4.99k
100
10
820pF
1
3418fc
For more information
www.linear.com/LTC3418
1
LTC3418
absoluTe MaxiMuM raTings
Input Supply Voltage ................................... –0.3V to 6V
I
TH
, RUN/SS, V
FB
Voltages ......................... –0.3V to V
IN
SYNC/MODE Voltages................................ –0.3V to V
IN
TRACK Voltage........................................... –0.3V to V
IN
SW Voltage .................................. –0.3V to (V
IN
+ 0.3V)
Operating Temperature Range
(Note 2) ...............................................–40°C to 85°C
Junction Temperature (Note 5) ............................. 125°C
Storage Temperature Range ................. –65°C to 125°C
(Note 1)
pin conFiguraTion
TOP VIEW
TRACK
PGND
PGND
PGND
PGND
PGND
PGND
31 SW
30 SW
29 PV
IN
28 PV
IN
27 SYNC/MODE
39
26 I
TH
25 V
FB
24 SV
IN
23 PV
IN
22 PV
IN
21 SW
20 SW
13 14 15 16 17 18 19
V
REF
PGND
PGND
PGND
PGND
PGND
PGND
38 37 36 35 34 33 32
SW 1
SW 2
PV
IN
3
PV
IN
4
PGOOD 5
R
T
6
RUN/SS 7
SGND 8
PV
IN
9
PV
IN
10
SW 11
SW 12
UHF PACKAGE
38-LEAD (7mm
×
5mm) PLASTIC QFN
T
JMAX
= 125°C,
θ
JA
= 34°C/W,
θ
JC
= 1°C/W
EXPOSED PAD (PIN 39) IS PGND, MUST BE SOLDERED TO PCB
orDer inForMaTion
LEAD FREE FINISH
LTC3418EUHF#PBF
TAPE AND REEL
LTC3418EUHF#TRPBF
http://www.linear.com/product/LTC3418#orderinfo
PART MARKING
3418
PACKAGE DESCRIPTION
38-Lead (7mm
×
5mm) Plastic QFN
TEMPERATURE RANGE
–40°C to 85°C
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/.
Some packages are available in 500 unit reels through
designated sales channels with #TRMPBF suffix.
2
3418fc
For more information
www.linear.com/LTC3418
LTC3418
elecTrical characTerisTics
SYMBOL
V
IN
V
FB
I
FB
∆V
FB
V
LOADREG
V
TRACK
I
TRACK
∆V
PGOOD
R
PGOOD
I
Q
f
OSC
f
SYNC
R
PFET
R
NFET
I
LIMIT
V
UVLO
V
REF
I
LSW
V
RUN
PARAMETER
Input Voltage Range
Regulated Feedback Voltage
Feedback Input Current
Reference Voltage Line Regulation
Output Voltage Load Regulation
Tracking Voltage Offset
Tracking Voltage Range
TRACK Input Current
Power Good Range
Power Good Resistance
Input DC Bias Current
Active Current
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
Reference Output
SW Leakage Current
RUN Threshold
V
RUN
= 0V, V
IN
= 5.5V
0.5
(Note 4)
V
FB
= 0.7V, V
ITH
= 1V
V
RUN
= 0V
R
OSC
= 69.8kΩ
(Note 6)
(Note 6)
I
SW
= 600mA
I
SW
= – 600mA
12
1.75
1.219
0.88
0.3
0.3
35
25
17
2
1.250
0.1
0.65
2.25
1.281
1
0.8
V
IN
= 2.5V to 5.5V (Note 3)
Measured in Servo Loop, V
ITH
= 0.36V
Measured in Servo Loop, V
ITH
= 0.84V
V
TRACK
= 0.4V
0
100
±7.5
100
380
0.03
1
l
l
The
l
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
IN
= 3.3V. (Note 2)
CONDITIONS
0°C ≤ T
A
≤ 85°C
(Note 3)
MIN
2.25
l
TYP
0.800
0.800
100
0.04
0.02
–0.02
MAX
5.5
0.808
0.816
200
0.2
0.2
–0.2
15
0.8
200
±9
150
450
1.5
1.12
4
4
50
35
UNITS
V
V
V
nA
%/V
%
%
mV
V
nA
%
Ω
µA
µA
MHz
MHz
MHz
mΩ
mΩ
A
V
V
µA
V
0.792
0.784
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 LTC3418 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.
Note 3:
The LTC3418 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 P
D
as follows:
LTC3418: T
J
= T
A
+ (P
D
)(34°C/W)
Note 6:
This parameter is guaranteed by design and characterization.
3418fc
For more information
www.linear.com/LTC3418
3
LTC3418
Typical perForMance characTerisTics
Internal Reference Voltage
vs Temperature
0.8000
0.7995
REFERENCE VOLTAGE (V)
ON-RESISTANCE (m )
T
A
= 25°C unless otherwise noted.
Switch On-Resistance
vs Input Voltage
45
40
ON-RESISTANCE (mΩ)
On-Resistance vs Temperature
50
45
40
V
IN
= 3.3V
V
IN
= 3.3V
0.7990
0.7985
0.7980
0.7975
0.7970
0.7965
0.7960
–40 –20
0
20 40 60 80
TEMPERATURE (°C)
100 120
3418 G01
35
30
25
20
15
10
5
0
2.25
2.75
PFET
NFET
35
30
25
20
15
10
5
PFET
NFET
3.25 3.75 4.25 4.75
INPUT VOLTAGE (V)
5.25
3418 G02
0
–40 –20
0
20 40 60 80
TEMPERATURE (°C)
100 120
3418 G03
Switch Leakage vs Input Voltage
5.0
4.5
500
450
400
300
250
200
150
100
50
0
Quiescent Current
vs Input Voltage
4500
4000
3500
Frequency vs R
OSC
V
IN
= 3.3V
QUIESCENT CURRENT (µA)
4.0
LEAKAGE CURRENT (nA)
3.0
2.5
2.0
1.5
1.0
0.5
0
2.25
2.75
NFET
PFET
FREQUENCY (kHz)
2.5
3
4
4.5
3.5
INPUT VOLTAGE (V)
5
5.5
3418 G05
3.5
350
3000
2500
2000
1500
1000
500
0
10
50
90
130
170
R
OSC
(k )
210
250
3418 G06
3.25 3.75 4.25 4.75
INPUT VOLTAGE (V)
5.25
3418 G04
Frequency vs Temperature
1100
1080
1060
FREQUENCY (kHz)
FREQUENCY (kHz)
Frequency vs Input Voltage
1100
1080
1060
EFFICIENCY (%)
Efficiency and Power Loss
vs Load Current
100
90
80
70
60
50
40
30
V
IN
= 3.3V
V
OUT
= 2.5V
0.1
1
LOAD CURRENT (A)
10
3418 G09
V
IN
= 3.3V
100000
EFFICIENCY
10000
POWER LOSS (mW)
1040
1020
1000
980
960
940
920
900
–40 –20
0
20 40 60 80
TEMPERATURE (°C)
100 120
3418 G07
1040
1020
1000
980
960
940
920
900
2.25
2.75
3.25 3.75 4.25 4.75
INPUT VOLTAGE (V)
5.25
3418 G08
1000
POWER LOSS
100
10
20
0.01
1
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3418fc
For more information
www.linear.com/LTC3418
LTC3418
Typical perForMance characTerisTics
Efficiency vs Load Current
100
90
80
Burst Mode OPERATION
100
90
80
3.3V
5V
T
A
= 25°C unless otherwise noted.
Efficiency vs Load Current
100
90
80
Efficiency vs Load Current
3.3V
5V
EFFICIENCY (%)
EFFICIENCY (%)
60
50
40
30
20
10
V
IN
= 3.3V
V
OUT
= 2.5V
60
50
40
30
20
10
FORCED CONTINUOUS
V
OUT
= 2.5V
0.1
1
LOAD CURRENT (A)
10
3418 G11
EFFICIENCY (%)
70
FORCED CONTINUOUS
70
70
60
50
40
30
20
10
Burst Mode OPERATION
V
OUT
= 2.5V
0.1
1
LOAD CURRENT (A)
10
3418 G12
0
0.01
0.1
1
LOAD CURRENT (A)
10
3418 G10
0
0.01
0
0.01
Peak Inductor Current
vs Burst Clamp Voltage
12
0
–0.05
ΔV
OUT
/V
OUT
(%)
Load Regulation
V
IN
= 3.3V
V
OUT
= 1.8V
f = 1MHz
Load Step Transient
OUTPUT
VOLTAGE
100mV/DIV
PEAK INDUCTOR CURRENT (A)
10
8
6
4
2
0
5V
3.3V
0
0.1
0.2
0.3 0.4 0.5
V
BCLAMP
(V)
0.6
0.7
0.8
–0.10
–0.15
–0.20
–0.25
–0.30
INDUCTOR
CURRENT
5A/DIV
V
IN
= 3.3V
20µs/DIV
V
OUT
= 2.5V
LOAD STEP: 800mA TO 8A
0
1
2
6
5
4
3
LOAD CURRENT (A)
7
8
3418 G15
3418 G13
3418 G14
Load Step Transient
OUTPUT
VOLTAGE
100mV/DIV
OUTPUT
VOLTAGE
100mV/DIV
Burst Mode Operation
Start-Up Transient
OUTPUT
VOLTAGE
500mV/DIV
INDUCTOR
CURRENT
5A/DIV
INDUCTOR
CURRENT
1A/DIV
V
IN
= 3.3V
40µs/DIV
V
OUT
= 2.5V
LOAD STEP: 3A TO 8A
3418 G16
INDUCTOR
CURRENT
2A/DIV
V
IN
= 3.3V
V
OUT
= 2.5V
LOAD: 200mA
20µs/DIV
3418 G17
V
IN
= 3.3V
V
OUT
= 2.5V
LOAD: 8A
1ms/DIV
3418 G18
3418fc
For more information
www.linear.com/LTC3418
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