FEATURES
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LTC3425
5A, 8MHz, 4-Phase
Synchronous Step-Up
DC/DC Converter
DESCRIPTIO
The LTC
®
3425 is a synchronous, 4-phase boost converter
with output disconnect capable of operation below 1V
input. It includes four N-channel MOSFET switches and
four P-channel synchronous rectifiers for an effective
R
DS(ON)
of 0.045Ω and 0.05Ω, respectively. 4-phase
operation greatly reduces peak inductor currents, and
capacitor ripple current, and increases effective switching
frequency, minimizing inductor and capacitor sizes. True
output disconnect eliminates inrush current and allows
zero load current in shutdown. External Schottky diodes
are not required in most applications (V
OUT
< 4.3V). Power
saving Burst Mode operation can be user controlled or left
in automatic mode.
Other features include 1µA shutdown current, program-
mable frequency with sync in and out, programmable
soft-start, antiringing control, thermal shutdown, adjust-
able current limit, reference output and power good
comparator.
The LTC3425 is available in a small, thermally enhanced
32-pin QFN package.
, LTC and LT are registered trademarks of Linear Technology Corporation.
Burst Mode is a registered trademark of Linear Technology Corporation.
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High Efficiency: Up to 95%
Up to 3A Continuous Output Current
4-Phase Operation for Low Output Ripple
and Tiny Solution Size
Output Disconnect and Inrush Current Limiting
Very Low Quiescent Current: 12µA
0.5V to 4.5V Input Range
2.4V to 5.25V Adjustable Output Voltage
Adjustable Current Limit
Adjustable, Fixed Frequency Operation from
100kHz to 2MHz per Phase
Synchronizable Oscillator with Sync Output
Internal Synchronous Rectifiers
Manual or Automatic Burst Mode
®
Operation
Power Good Comparator
<1µA Shutdown Current
Antiringing Control
5mm
×
5mm Thermally Enhanced QFN Package
APPLICATIO S
s
s
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Handheld Computers
Point-of-Load Regulators
3.3V to 5V Conversion
TYPICAL APPLICATIO
V
IN
2V TO 3V
2.2µF
2.7µH
2.7µH
2.7µH
2.7µH
V
IN
OFF ON
SHDN
REFOUT
CCM
REFEN
SYNCIN
BURST
0.01µF
15k
20k
75k
R
T
I
LIM
SGND
SWA
SWB
SWC
EFFICIENCY (%)
SWD
V
OUTS
V
OUTA
V
OUTB
V
OUTC
V
OUTD
4.7µF
×4
1M
10k
V
OUT
3.3V
2A
LTC3425
FB
COMP
SS
SYNCOUT
PGOOD
GNDC GNDD
22pF
330pF
33k
0.01µF
3425 TA01
590k
GNDA
GNDB
C
IN
: TAIYO YUDEN JMK107BJ225MA
C
OUT
: TAIYO YUDEN JMK212BJ475MG (×4)
L1-L4: TDK RLF5018T-2R7M1R8
3425f
U
U
U
100
90
80
70
60
50
40
30
V
IN
= 2.4V
V
OUT
= 3.3V
10 f = 1MHz/PHASE
L = 2.7µH
0
1
10
100
1000
0.1
LOAD CURRENT (mA)
20
Burst Mode
OPERATION
FIXED
FREQUENCY
MODE
10000
3425 TA02
1
LTC3425
ABSOLUTE
(Note 1)
AXI U RATI GS
PACKAGE/ORDER I FOR ATIO
SYNCOUT
V
IN
Voltage ................................................. – 0.3V to 6V
SWA-D Voltages ..........................................– 0.3V to 6V
V
OUTA-D
, V
OUTS
Voltages............................ – 0.3V to 6V
BURST, SHDN, SS, REFEN, SYNCOUT, PGOOD,
REFOUT, CCM, SYNCIN Voltages ............... – 0.3V to 6V
Operating Ambient Temperature Range
(Note 5) .............................................. – 40°C to 85°C
Storage Temperature Range ................. – 65°C to 125°C
Lead Temperature (Soldering, 10 sec).................. 300°C
TOP VIEW
SYNCIN
SHDN
CCM
I
LIM
V
IN
SS
R
T
32 31 30 29 28 27 26 25
GNDA 1
GNDA 2
SWA 3
V
OUTA
4
V
OUTB
5
SWB 6
GNDB 7
GNDB 8
9 10 11 12 13 14 15 16
REFEN
SGND
REFOUT
PGOOD
FB
COMP
BURST
V
OUTS
24 GNDD
23 GNDD
22 SWD
33
21 V
OUTD
20 V
OUTC
19 SWC
18 GNDC
17 GNDC
UH PACKAGE
32-LEAD (5mm
×
5mm) PLASTIC QFN
T
JMAX
= 125°C,
θ
JA
= 40°C/W 1 LAYER BOARD,
θ
JA
= 35°C/W 4 LAYER BOARD,
θ
JC
= 1.1°C/W
EXPOSED PAD IS GND (PIN 33) MUST BE SOLDERED TO PCB
ORDER PART
NUMBER
LTC3425EUH
UH PART
MARKING
3425
Consult LTC Marketing for parts specified with wider operating temperature ranges.
The
q
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
IN
= 1.2V, V
OUT
= 3.3V, R
T
= 15k, unless otherwise noted.
PARAMETER
Minimum Start-Up Voltage
Minimum Operating Voltage
Output Voltage Adjust Range
Feedback Regulation Voltage
Feedback Input Current
V
OUT
Quiescent Current—Burst Mode Operation
V
IN
Quiescent Current—Shutdown
V
OUT
Quiescent Current—Active
NMOS Switch Leakage
PMOS Switch Leakage
NMOS Switch On Resistance
PMOS Switch On Resistance
NMOS Current Limit
BURST = 0V, REFEN = 0V, FB = 1.3V (Note 2)
BURST = 0V, REFEN = 2V, FB = 1.3V (Note 2)
SHDN = 0V, V
OUT
= 0V, Not Including Switch Leakage
V
C
= 0V, Nonswitching (Note 2)
V
SW
= 5V
V
SW
= 5V, V
OUT
= 0V
(Note 4)
(Note 4)
I
LIM
Resistor = 75k (Note 4)
I
LIM
Resistor = 200k (Note 4)
q
q
ELECTRICAL CHARACTERISTICS
CONDITIONS
V
OUT
= 0V, I
LOAD
< 1mA
(Note 3)
q
q
q
MIN
TYP
0.88
MAX
1
0.5
5.25
UNITS
V
V
V
V
nA
µA
µA
µA
mA
µA
µA
Ω
Ω
A
A
2.4
1.196
1.220
1
12
18
0.1
1.8
0.1
0.1
0.04
0.05
5.0
1.8
7.0
2.7
1.244
50
25
35
1
3
5
10
2
U
3425f
W
U
U
W W
W
LTC3425
The
q
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
IN
= 1.2V, V
OUT
= 3.3V, R
T
= 15k, unless otherwise noted.
PARAMETER
PMOS Turn-Off Current
PMOS Reverse Current Limit
Max Duty Cycle
Min Duty Cycle
Frequency Accuracy
SHDN Input High
SHDN Input Low
SHDN Input Current
REFEN, CCM Input High
REFEN, CCM Input Low
REFEN, Input Current
SYNCIN Input High
SYNCIN Input Low
SYNCIN Input Current
CCM Input Current
SYNC Input Pulse Width Range
SYNC Out High
SYNC Out Low
REFOUT
Error Amp Transconductance
Error Amp Output High
Error Amp Output Low
PGOOD Threshold (Falling Edge)
PGOOD Hysteresis
PGOOD Low Voltage
PGOOD Leakage
SS Current Source
Burst Threshold Voltage
Burst Threshold Hysteresis
Note 1:
Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
Note 2:
Current is measured into the V
OUTS
pin since the supply current is
bootstrapped to the output. The current will reflect to the input supply by
V
OUT
/(V
IN
• Efficiency). The outputs are not switching.
Note 3:
Once the output is started, the IC is not dependent on the V
IN
supply.
Note 4:
Total with all four FETs in parallel.
Referenced to Feedback Voltage
Referenced to Feedback Voltage
I
SINK
= 1mA (10mA Max)
V
PGOOD
= 5.5V
V
SS
= 1V
Falling Edge
q
q
q
q
q
ELECTRICAL CHARACTERISTICS
CONDITIONS
CCM < 0.4V
CCM > 1.4V
q
q
MIN
TYP
–80
0.6
MAX
UNITS
mA
A
83
0.8
1
0.65
90
1
97
0
1.2
%
%
MHz
V
V
R
T
= 15k
V
OUT
= 0V (Initial Start-Up)
V
OUT
> 2.4V
V
SHDN
= 5V or 0V
V
SHDN
= 2V
q
q
q
q
0.25
0.01
–0.50
1
V
µA
µA
V
V
µA
V
V
µA
µA
µs
V
q
q
1.4
0.4
0.01
1
0.5
0.3
2
1
4
2.5
V
REFEN
= 5V
(Note 7)
(Note 7)
V
SYNCIN
= 5V
V
CCM
= 5V
q
q
q
0.1
3
0.4
V
V
V
µS
V
V
REFEN > 1.4V, No Load
I
SOURCE
< 100µA, I
SINK
< 10µA
I
LIM
Resistor = 75k
q
q
1.190
1.184
1.220
1.220
50
2.2
0.15
1.251
1.252
–9.5
1.5
–11.4
2.5
0.12
0.01
2.7
–13.5
4
0.25
1
1.04
%
%
V
µA
µA
V
mV
0.84
0.94
120
Note 5:
The LTC3425E is guaranteed to meet performance specifications
from 0°C to 70°C. Specifications over the –40°C to 85°C operating
temperature range are assured by design, characterization and correlation
with statistical process controls.
Note 6:
This IC includes overtemperature protection that is intended to
protect the device during momentary overload conditions. Junction
temperature will exceed 125°C when overtemperature protection is active.
Continuous operation above the specified maximum operating junction
temperature may impair device reliability.
Note 7:
The typical logic threshold for this input is: V
OUT
/2
3425f
3
LTC3425
TYPICAL PERFOR A CE CHARACTERISTICS
SWA, SWB, SWC, SWD
at 1MHz/Phase
SW Pin and Inductor Current in
Discontinous Mode. Antiring
Circuit Eliminates High Frequency
Ringing
SWA TO SWD
5V/DIV
250ns/DIV
Transient Response 0.5A to 1.5A
Fixed Frequency Mode Operation
V
OUT
AC
100mV/DIV
V
OUT
AC
50mV/DIV
LOAD
CURRENT
0.5A/DIV
V
IN
= 2.4V
V
OUT
= 3.3V
C
OUT
= 220µF
100µs/DIV
Soft-Start and Inrush Current
Limiting
I
IN
0.5A/DIV
SS Pin
1V/DIV
V
OUT
2V/DIV
V
OUT
AC
50mV/DIV
V
IN
= 2.4V
500µs/DIV
V
OUT
= 3.3V
C
SOFTSTART
= 0.015µF
4
U W
SW Pin and Oscillator SYNCOUT
SWA
2V/DIV
SYNCOUT
2V/DIV
I
L
0.2A/DIV
SW
2V/DIV
3425 G01
250ns/DIV
3425 G02
V
IN
= 2.4V
V
OUT
= 3.3V
C
OUT
= 220µF
250ns/DIV
3425 G03
Output Voltage Ripple at 2.5A
Load with Only Four 4.7µF
Ceramic Capacitors
Output Voltage Ripple at 2.5A
Load with a 47µF Ceramic Bulk
Capacitor
V
OUT
AC
10mV/DIV
3425 G04
V
IN
= 2.4V
500ns/DIV
V
OUT
= 3.3V
FREQUENCY = 1MHz/PHASE
3425 G05
V
IN
= 2.4V
500ns/DIV
V
OUT
= 3.3V
FREQUENCY = 1MHz/PHASE
3425 G06
Burst Mode Operation
I
OUT
1A/DIV
SWA
2V/DIV
BURST PIN
1V/DIV
Transient Response 10mA to 1A
Automatic Burst Mode Operation
V
OUT
AC
200mV/DIV
V
IN
= 2.4V
V
OUT
= 3.3V
C
OUT
= 220µF
25µs/DIV
3425 G07
3425 G08
V
IN
= 2.4V
V
OUT
= 3.3V
C
OUT
= 220µF
1ms/DIV
3425 G10
3425f
LTC3425
TYPICAL PERFOR A CE CHARACTERISTICS
Converter Efficiency
for V
OUT
= 3.3V
100
90
80
EFFICIENCY (%)
100
V
IN
= 2.4V
V
IN
= 1.2V
EFFICIENCY (%)
60
50
40
30
20
10
0
0.1
T
A
= 25°C
1
V
IN
= 2.4V
V
IN
= 1.2V
60
50
40
30
20
V
IN
= 3.3V
V
IN
= 2.4V
EFFICIENCY (%)
70
Burst Mode OPERATION
1MHz/PHASE
10
100
1000
OUTPUT CURRENT (mA)
10000
3425 G11
Efficiency Comparison of
Discontinuous Mode and Forced
Continuous Mode at Light Loads
for V
IN
= 2.4V, V
OUT
= 3.3V
100
T
A
= 25°C
90 1MHz/PHASE
80 DISCONTINUOUS
MODE
70
60
50
40
30
20
10
0
1
10
100
1000
CONVERTER OUTPUT CURRENT (mA)
3425 G14
CONVERTER INPUT CURRENT (µA)
EFFICIENCY (%)
EFFICIENCY (%)
FORCED
CONTINUOUS
MODE
Oscillator Frequency
10
T
A
= 25°C
1.8
1.6
1.4
1.2
1.0
0.8
0.6
R
DS(ON)
(ALL FOUR PHASES IN PARALLEL)
PEAK CURRENT IN EACH PHASE (A)
FREQUENCY (MHz)
1
1
10
R
T
(kΩ)
100
3425 G17
U W
Converter Efficiency
for V
OUT
= 5V
98
V
IN
= 3.3V
V
IN
= 2.4V
90
80
70
Converter Efficiency for 2-, 3- and
4-Phase Operation
T
A
= 25°C
96 V
IN
= 2.4V
V
OUT
= 3.3V
94 1MHz/PHASE
92
90
4 PHASE
88
86
2 PHASE
84
3 PHASE
10
T
A
= 25°C
0
0.1
1
Burst Mode OPERATION
1MHz/PHASE
10
100
1000
OUTPUT CURRENT (mA)
10000
3425 G12
82
80
100
1000
LOAD (mA)
10000
3425 G13
Efficiency Comparison of
Discontinuous Mode and Forced
Continuous Mode at Light Loads
for V
IN
= 3.3V, V
OUT
= 5V
100
T
A
= 25°C
90 1MHz/PHASE
80
70
60
50
40
30
20
10
0
1
10
LOAD (mA)
3425 G15
Converter No Load Input Current
vs V
IN
(Burst Mode Operation)
140
120
100
80
60
V
OUT
= 3.3V
40
20
0
1.5
V
OUT
= 5V
T
A
= 25°C
DISCONTINUOUS
MODE
FORCED
CONTINUOUS
MODE
100
1000
2.0
2.5
3.0
V
IN
(V)
3.5
4.0
4.5
3425 G16
Peak Current Limit
T
A
= 25°C
Effective R
DS(ON)
0.065
T
A
= 25°C
0.060
PMOS
0.055
0.050
NMOS
0.045
60
80
100 120 140 160
I
LIM
RESISTOR (kΩ)
180
200
0.040
2.5
3
4
3.5
V
OUT
(V)
4.5
5
3425 G19
3425 G18
3425f
5
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