LTC3418
8A, 4MHz, Monolithic
Synchronous Step-Down
Regulator
Description
Features
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High Efficiency: Up to 95%
8A Output Current
2.25V to 5.5V Input Voltage Range
Low RDS(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
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 continuous 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.
Typical Application
2.5V/8A Step-Down Regulator
Efficiency and Power Loss vs Load Current
100
CIN
47µF
×4
SVIN TRACK PVIN
2.2M
30.1k
1000pF
0.2µH
SW
COUT
100µF
×2
LTC3418
PGOOD
PGND
RUN/SS
SGND
ITH
4.99k
820pF
SYNC/MODE VFB
332Ω
EFFICIENCY
10000
80
70
60
1000
POWER LOSS
100
50
40
4.32k
3418 TA01a
1.69k
VOUT
2.5V
8A
100000
10
30
20
0.01
VIN = 3.3V
VOUT = 2.5V
0.1
1
LOAD CURRENT (A)
10
3418 TA01b
For more information www.linear.com/LTC3418
POWER LOSS (mW)
RT
90
EFFICIENCY (%)
VIN
2.8V TO 5.5V
1
3418fc
1
LTC3418
Absolute Maximum Ratings
Pin Configuration
(Note 1)
PGND
PGND
PGND
TRACK
PGND
PGND
TOP VIEW
PGND
Input Supply Voltage.................................... –0.3V to 6V
ITH, RUN/SS, VFB Voltages.......................... –0.3V to VIN
SYNC/MODE Voltages................................. –0.3V to VIN
TRACK Voltage........................................... –0.3V to VIN
SW Voltage................................... –0.3V to (VIN + 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
38 37 36 35 34 33 32
SW 1
31 SW
SW 2
30 SW
PVIN 3
29 PVIN
PVIN 4
28 PVIN
PGOOD 5
27 SYNC/MODE
RT 6
26 ITH
39
RUN/SS 7
25 VFB
SGND 8
24 SVIN
PVIN 9
23 PVIN
PVIN 10
22 PVIN
SW 11
21 SW
20 SW
SW 12
PGND
PGND
PGND
VREF
PGND
PGND
PGND
13 14 15 16 17 18 19
UHF PACKAGE
38-LEAD (7mm × 5mm) PLASTIC QFN
TJMAX = 125°C, θJA = 34°C/W, θJC = 1°C/W
EXPOSED PAD (PIN 39) IS PGND, MUST BE SOLDERED TO PCB
order information
http://www.linear.com/product/LTC3418#orderinfo
LEAD FREE FINISH
TAPE AND REEL
PART MARKING
PACKAGE DESCRIPTION
TEMPERATURE RANGE
LTC3418EUHF#PBF
LTC3418EUHF#TRPBF
3418
38-Lead (7mm × 5mm) Plastic QFN
–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
The
l denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VIN = 3.3V. (Note 2)
SYMBOL
PARAMETER
VIN
Input Voltage Range
VFB
Regulated Feedback Voltage
CONDITIONS
MIN
TYP
2.25
0°C ≤ TA ≤ 85°C
(Note 3)
IFB
Feedback Input Current
∆VFB
Reference Voltage Line Regulation
VIN = 2.5V to 5.5V (Note 3)
VLOADREG
Output Voltage Load Regulation
Measured in Servo Loop, VITH = 0.36V
Measured in Servo Loop, VITH = 0.84V
VTRACK
Tracking Voltage Offset
VTRACK = 0.4V
Tracking Voltage Range
l
0.792
0.784
l
l
MAX
UNITS
5.5
V
0.800
0.800
0.808
0.816
V
V
100
200
nA
0.04
0.2
%/V
0.02
–0.02
0.2
–0.2
%
%
15
mV
0.8
V
200
nA
0
ITRACK
TRACK Input Current
100
∆VPGOOD
Power Good Range
±7.5
±9
%
RPGOOD
Power Good Resistance
100
150
Ω
IQ
Input DC Bias Current
Active Current
Shutdown
(Note 4)
VFB = 0.7V, VITH = 1V
VRUN = 0V
380
0.03
450
1.5
µA
µA
fOSC
Switching Frequency
Switching Frequency Range
ROSC = 69.8kΩ
(Note 6)
0.88
0.3
1
1.12
4
MHz
MHz
fSYNC
SYNC Capture Range
(Note 6)
0.3
4
MHz
RPFET
RDS(ON) of P-Channel FET
ISW = 600mA
35
50
mΩ
RNFET
RDS(ON) of N-Channel FET
ISW = – 600mA
25
35
mΩ
ILIMIT
Peak Current Limit
VUVLO
12
17
Undervoltage Lockout Threshold
1.75
2
2.25
V
VREF
Reference Output
1.219
1.250
1.281
V
ILSW
SW Leakage Current
0.1
1
µA
VRUN
RUN Threshold
0.5
0.65
0.8
V
VRUN = 0V, VIN = 5.5V
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.
A
Note 3: The LTC3418 is tested in a feedback loop that adjusts V FB to
achieve a specified error amplifier output voltage (ITH).
Note 4: Dynamic supply current is higher due to the internal gate charge
being delivered at the switching frequency.
Note 5: TJ is calculated from the ambient temperature TA and power
dissipation PD as follows:
LTC3418: TJ = TA + (PD)(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
Switch On-Resistance
vs Input Voltage
VIN = 3.3V
50
40
45
0.7985
0.7980
0.7975
0.7970
VIN = 3.3V
40
35
0.7990
ON-RESISTANCE (mΩ)
REFERENCE VOLTAGE (V)
0.7995
On-Resistance vs Temperature
45
PFET
30
ON-RESISTANCE (mΩ)
0.8000
TA = 25°C unless otherwise noted.
NFET
25
20
15
10
PFET
35
NFET
30
25
20
15
10
0.7965
5
5
0.7960
–40 –20
0
2.25
0
–40 –20
0
20 40 60 80
TEMPERATURE (°C)
100 120
2.75
3.25 3.75 4.25 4.75
INPUT VOLTAGE (V)
5.25
3418 G01
Quiescent Current
vs Input Voltage
4500
4.5
450
4000
4.0
400
3.5
3.0
2.5
NFET
PFET
0.5
0
2.25
3.25 3.75 4.25 4.75
INPUT VOLTAGE (V)
2.75
300
250
200
150
3
2.5
4
4.5
3.5
INPUT VOLTAGE (V)
960
940
100
1080
90
1040
1020
1000
980
960
920
920
900
–40 –20
900
2.25
100 120
3418 G07
4
100000
EFFICIENCY
10000
70
60
1000
POWER LOSS
100
50
40
10
30
2.75
3.25 3.75 4.25 4.75
INPUT VOLTAGE (V)
250
210
80
940
20 40 60 80
TEMPERATURE (°C)
130
170
ROSC (kΩ)
3418 G06
1100
EFFICIENCY (%)
FREQUENCY (kHz)
980
90
Efficiency and Power Loss
vs Load Current
1060
1000
50
5.25
3418 G08
20
0.01
POWER LOSS (mW)
FREQUENCY (kHz)
1060
1020
10
3418 G05
VIN = 3.3V
0
0
5.5
5
Frequency vs Input Voltage
1040
1500
500
Frequency vs Temperature
1080
2000
50
3418 G04
1100
2500
1000
5.25
VIN = 3.3V
3000
100
0
Frequency vs ROSC
3500
350
FREQUENCY (kHz)
QUIESCENT CURRENT (µA)
LEAKAGE CURRENT (nA)
500
1.0
100 120
3418 G03
5.0
1.5
20 40 60 80
TEMPERATURE (°C)
3418 G02
Switch Leakage vs Input Voltage
2.0
0
VIN = 3.3V
VOUT = 2.5V
0.1
1
LOAD CURRENT (A)
10
1
3418 G09
3418fc
For more information www.linear.com/LTC3418
LTC3418
Typical Performance Characteristics
Efficiency vs Load Current
100
Efficiency vs Load Current
50
40
30
20
70
60
50
40
30
20
VIN = 3.3V
VOUT = 2.5V
10
0
0.01
FORCED CONTINUOUS
VOUT = 2.5V
0
0.01
10
0.1
1
LOAD CURRENT (A)
3418 G10
10
–0.05
8
–0.10
ΔVOUT/VOUT (%)
PEAK INDUCTOR CURRENT (A)
0
6
4
5V
0.1
0.2
0.3 0.4 0.5
VBCLAMP (V)
30
10
10
0.6
0.7
0.8
0
0.01
INDUCTOR
CURRENT
5A/DIV
–0.20
–0.30
VIN = 3.3V
20µs/DIV
VOUT = 2.5V
LOAD STEP: 800mA TO 8A
0
1
2
6
5
4
3
LOAD CURRENT (A)
7
3418 G15
8
3418 G14
Start-Up Transient
OUTPUT
VOLTAGE
100mV/DIV
OUTPUT
VOLTAGE
500mV/DIV
INDUCTOR
CURRENT
1A/DIV
3418 G16
10
3418 G12
Burst Mode Operation
INDUCTOR
CURRENT
5A/DIV
0.1
1
LOAD CURRENT (A)
OUTPUT
VOLTAGE
100mV/DIV
–0.15
Load Step Transient
OUTPUT
VOLTAGE
100mV/DIV
Burst Mode OPERATION
VOUT = 2.5V
Load Step Transient
VIN = 3.3V
VOUT = 1.8V
f = 1MHz
3418 G13
VIN = 3.3V
40µs/DIV
VOUT = 2.5V
LOAD STEP: 3A TO 8A
40
–0.25
3.3V
0
50
Load Regulation
12
0
60
3418 G11
Peak Inductor Current
vs Burst Clamp Voltage
2
70
20
10
0.1
1
LOAD CURRENT (A)
5V
80
5V
EFFICIENCY (%)
FORCED CONTINUOUS
60
3.3V
90
3.3V
80
EFFICIENCY (%)
EFFICIENCY (%)
100
90
80
70
Efficiency vs Load Current
100
Burst Mode OPERATION
90
TA = 25°C unless otherwise noted.
INDUCTOR
CURRENT
2A/DIV
VIN = 3.3V
VOUT = 2.5V
LOAD: 200mA
20µs/DIV
3418 G17
VIN = 3.3V
VOUT = 2.5V
LOAD: 8A
1ms/DIV
3418 G18
3418fc
For more information www.linear.com/LTC3418
5
LTC3418
Pin Functions
SW (Pins 1, 2, 11, 12, 20, 21, 30, 31): Switch Node Connection to Inductor. This pin connects to the drains of the
internal main and synchronous power MOSFET switches.
PVIN (Pins 3, 4, 9, 10, 22, 23, 28, 29): Power Input
Supply. Decouple these pins to PGND with capacitors on
all four corners of the package.
PGOOD (Pin 5): Power Good Output. Open-drain logic
output that is pulled to ground when the output voltage
is not within ±7.5% of regulation point.
VREF (Pin 16): Reference Output. Decouple this pin with
a 2.2µF capacitor.
SVIN (Pin 24): Signal Input Supply. Decouple this pin to
SGND with a capacitor.
VFB (Pin 25): Feedback Pin. Receives the feedback voltage from a resistive divider connected across the output.
RT (Pin 6): Oscillator Resistor Input. Connecting a resistor to ground from this pin sets the switching frequency.
ITH (Pin 26): Error Amplifier Compensation Point. The
current comparator threshold increases with this control
voltage. Nominal voltage range for this pin is from 0.2V
to 1.4V with 0.4V corresponding to the zero-sense voltage
(zero current).
RUN/SS (Pin 7): Run Control and Soft-Start Input. Forcing
this pin below 0.5V shuts down the LTC3418. In shutdown
all functions are disabled drawing
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