LTC3418
8A, 4MHz, Monolithic
Synchronous Step-Down
Regulator
DESCRIPTIO
The LTC
®
3418 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 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 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
requirements of the application. A tracking input in the
LTC3418 allows for proper sequencing with respect to
another power supply.
, LTC and LT 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.
FEATURES
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■
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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
APPLICATIO S
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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 APPLICATIO
V
IN
2.8V TO 5.5V
Efficiency and Power Loss vs Load Current
100
90
EFFICIENCY
100000
2.5V/8A Step-Down Regulator
C
IN
100µF
0.2µH
C
OUT
100µF
×2
SV
IN
TRACK PV
IN
R
T
2.2M
30.1k
SW
LTC3418
PGOOD
PGND
RUN/SS
SGND
I
TH
SYNC/MODE V
FB
332Ω
1.69k
4.32k
EFFICIENCY (%)
V
OUT
2.5V
8A
80
70
60
50
40
30
V
IN
= 3.3V
V
OUT
= 2.5V
0.1
1
LOAD CURRENT (A)
10
3418 TA01b
1000pF
4.99k
820pF
3418 TA01a
20
0.01
U
U
U
10000
POWER LOSS (mW)
1000
POWER LOSS
100
10
1
3418f
1
LTC3418
ABSOLUTE
MAXIMUM
RATINGS
(Note 1)
PACKAGE/ORDER INFORMATION
TOP VIEW
TRACK
PGND
PGND
PGND
PGND
PGND
PGND
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 Ambient 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
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
13 14 15 16 17 18 19
PGND
PGND
PGND
V
REF
PGND
PGND
PGND
39
31 SW
30 SW
29 PV
IN
28 PV
IN
27 SYNC/MODE
26 I
TH
25 V
FB
24 SV
IN
23 PV
IN
22 PV
IN
21 SW
20 SW
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 AND MUST BE SOLDERED TO PCB
ORDER PART NUMBER
UH PART MARKING
LTC3418EUHF
3418
Consult LTC Marketing for parts specified with wider operating temperature ranges.
ELECTRICAL CHARACTERISTICS
SYMBOL
V
IN
V
FB
I
FB
∆V
FB
V
LOADREG
V
TRACK
I
TRACK
∆V
PGOOD
R
PGOOD
I
Q
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
The
●
indicates 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)
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
(Note 4)
V
FB
= 0.7V, V
ITH
= 1V
V
RUN
= 0V
380
0.03
●
●
MIN
2.25
●
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
UNITS
V
V
V
nA
%/V
%
%
mV
V
nA
%
Ω
µA
µA
3418f
0.792
0.784
2
U
W
U
U
W W
W
LTC3418
ELECTRICAL CHARACTERISTICS
SYMBOL
f
OSC
f
SYNC
R
PFET
R
NFET
I
LIMIT
V
UVLO
V
REF
I
LSW
V
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
Reference Output
SW Leakage Current
RUN Threshold
The
●
indicates specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
IN
= 3.3V. (Note 2)
CONDITIONS
R
OSC
= 69.8kΩ
(Note 6)
(Note 6)
I
SW
= 600mA
I
SW
= – 600mA
12
1.75
1.219
V
RUN
= 0V, V
IN
= 5.5V
0.5
MIN
0.88
0.3
0.3
35
25
17
2
1.250
0.1
0.65
2.25
1.281
1
0.8
TYP
1
MAX
1.12
4
4
50
35
UNITS
MHz
MHz
MHz
mΩ
mΩ
A
V
V
µA
V
Note 1:
Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
Note 2:
The LTC3418 is guaranteed to meet performance specifications
from 0
o
C to 70
o
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.
TYPICAL PERFOR A CE CHARACTERISTICS
Internal Reference Voltage
vs Temperature
0.8000
0.7995
V
IN
= 3.3V
45
40
REFERENCE VOLTAGE (V)
ON-RESISTANCE (mΩ)
PFET
30
NFET
25
20
15
10
5
ON-RESISTANCE (mΩ)
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 G07
U W
T
A
= 25°C unless otherwise noted.
Switch On-Resistance
vs Input Voltage
50
45
40
35
30
25
20
15
10
5
2.75
3.25 3.75 4.25 4.75
INPUT VOLTAGE (V)
5.25
3418 G01
On-Resistance vs Temperature
V
IN
= 3.3V
35
PFET
NFET
0
2.25
0
–40 –20
0
20 40 60 80
TEMPERATURE (°C)
100 120
3418 G02
3418f
3
LTC3418
TYPICAL PERFOR A CE CHARACTERISTICS
Switch Leakage vs Input Voltage
5.0
4.5
QUIESCENT CURRENT (µA)
500
450
400
FREQUENCY (kHz)
350
300
250
200
150
100
50
4.0
LEAKAGE CURRENT (nA)
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0
2.25
2.75
3.25 3.75 4.25 4.75
INPUT VOLTAGE (V)
5.25
3418 G03
NFET
PFET
Frequency vs Temperature
1100
1080
1060
FREQUENCY (kHz)
FREQUENCY (kHz)
1040
1020
1000
980
960
940
920
900
–40 –20
0
20 40 60 80
TEMPERATURE (°C)
100 120
3418 G06
V
IN
= 3.3V
EFFICIENCY (%)
Efficiency vs Load Current
100
90
80
EFFICIENCY (%)
Burst Mode OPERATION
70
EFFICIENCY (%)
60
50
40
30
20
10
V
IN
= 3.3V
V
OUT
= 2.5V
FORCED CONTINUOUS
60
50
40
30
20
10
FORCED CONTINUOUS
V
OUT
= 2.5V
0.1
1
LOAD CURRENT (A)
10
3418 G11
EFFICIENCY (%)
0
0.01
0.1
1
LOAD CURRENT (A)
4
U W
3418 G10
T
A
= 25°C unless otherwise noted.
Quiescent Current
vs Input Voltage
4500
4000
3500
3000
2500
2000
1500
1000
500
0
Frequency vs R
OSC
V
IN
= 3.3V
0
2.5
3
4
4.5
3.5
INPUT VOLTAGE (V)
5
5.5
3418 G04
10
50
90
130
170
R
OSC
(kΩ)
210
250
3418 G08
Frequency vs Input Voltage
1100
1080
1060
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 G05
Efficiency and Power Loss
vs Load Current
100
90
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
100000
EFFICIENCY
10000
POWER LOSS (mW)
1000
POWER LOSS
100
10
1
Efficiency vs Load Current
100
90
3.3V
80
70
5V
80
70
60
50
40
30
20
10
100
90
Efficiency vs Load Current
3.3V
5V
10
0
0.01
0
0.01
Burst Mode OPERATION
V
OUT
= 2.5V
0.1
1
LOAD CURRENT (A)
10
3418 G12
3418f
LTC3418
TYPICAL PERFOR A CE CHARACTERISTICS
Peak Inductor Current
vs Burst Clamp Voltage
12
PEAK INDUCTOR CURRENT (A)
10
∆V
OUT
/V
OUT
(%)
8
6
4
2
0
0
0.1
0.2
5V
3.3V
0.3 0.4 0.5
V
BCLAMP
(V)
0.6
0.7
0.8
–0.30
0
1
2
6
5
4
3
LOAD CURRENT (A)
7
8
Load Step Transient
OUTPUT
VOLTAGE
100mV/DIV
INDUCTOR
CURRENT
5A/DIV
V
IN
= 3.3V
40µs/DIV
V
OUT
= 2.5V
LOAD STEP: 3A TO 8A
PI FU CTIO S
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.
PV
IN
(Pins 3, 4, 9, 10, 22, 23, 28, 29):
Power Input
Supply. Decouple this pin to PGND with a capacitor.
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.
R
T
(Pin 6):
Oscillator Resistor Input. Connecting a resistor
to ground from this pin sets the switching frequency.
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 <1.5µA of supply cur-
rent. A capacitor to ground from this pin sets the ramp
time to full output current.
SGND (Pin 8):
Signal Ground. All small-signal compo-
nents and compensation components should connect to
this ground, which in turn connects to PGND at one point.
PGND (Pins 13, 14, 15, 17, 18, 19, 32, 33, 34, 36, 37,
38):
Power Ground. Connect this pin closely to the (–)
terminal of C
IN
and C
OUT
.
V
REF
(Pin 16):
Reference Output. Decouple this pin with a
2.2µF capacitor.
SV
IN
(Pin 24):
Signal Input Supply. Decouple this pin to
SGND with a capacitor.
3418f
U W
3418 G13
T
A
= 25°C unless otherwise noted.
Load Regulation
0
–0.05
–0.10
–0.15
–0.20
–0.25
V
IN
= 3.3V
V
OUT
= 1.8V
f = 1MHz
Load Step Transient
OUTPUT
VOLTAGE
100mV/DIV
INDUCTOR
CURRENT
5A/DIV
V
IN
= 3.3V
20µs/DIV
V
OUT
= 2.5V
LOAD STEP: 800mA TO 8A
3418 G15
3418 G14
Burst Mode Operation
Start-Up Transient
OUTPUT
VOLTAGE
100mV/DIV
OUTPUT
VOLTAGE
500mV/DIV
INDUCTOR
CURRENT
1A/DIV
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
U
U
U
5
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