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PDF LTC3425 Data sheet ( Hoja de datos )
| Número de pieza | LTC3425 | |
| Descripción | 5A 8MHz 4-Phase Synchronous Step-Up DC/DC Converter | |
| Fabricantes | Linear Technology | |
| Logotipo |  |
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FEATURES
s High Efficiency: Up to 95%
s Up to 3A Continuous Output Current
s 4-Phase Operation for Low Output Ripple
and Tiny Solution Size
s Output Disconnect and Inrush Current Limiting
s Very Low Quiescent Current: 12µA
s 0.5V to 4.5V Input Range
s 2.4V to 5.25V Adjustable Output Voltage
s Adjustable Current Limit
s Adjustable, Fixed Frequency Operation from
100kHz to 2MHz per Phase
s Synchronizable Oscillator with Sync Output
s Internal Synchronous Rectifiers
s Manual or Automatic Burst Mode® Operation
s Power Good Comparator
s <1µA Shutdown Current
s Antiringing Control
s
5mm
×
5mm
Thermally
U
Enhanced
QFN
Package
APPLICATIO S
s Handheld Computers
s Point-of-Load Regulators
s 3.3V to 5V Conversion
LTC3425www.DataSheet4U.com
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
RDS(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 (VOUT < 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.
TYPICAL APPLICATIO
VIN
2V TO 3V
2.2µF
2.7µH 2.7µH 2.7µH 2.7µH
OFF ON
0.01µF
20k
15k
75k
VIN
SHDN
REFOUT
CCM
REFEN
SYNCIN
BURST
RT
ILIM
SGND
SWA
SWB
SWC
SWD
VOUTS
VOUTA
VOUTB
VOUTC
VOUTD
LTC3425
GNDA
GNDB
FB
COMP
SS
SYNCOUT
PGOOD
GNDC GNDD
4.7µF
×4 1M
VOUT
3.3V
2A
10k
22pF
330pF
590k
33k
0.01µF
CIN: TAIYO YUDEN JMK107BJ225MA
COUT: TAIYO YUDEN JMK212BJ475MG (×4)
L1-L4: TDK RLF5018T-2R7M1R8
3425 TA01
100
90
80
Burst Mode FIXED
70 OPERATION FREQUENCY
MODE
60
50
40
30
20
VIN = 2.4V
VOUT = 3.3V
10 f = 1MHz/PHASE
L = 2.7µH
0
0.1 1 10
100 1000 10000
LOAD CURRENT (mA)
3425 TA02
3425f
1
1 page  
TYPICAL PERFOR A CE CHARACTERISTICS
LTC3425www.DataSheet4U.com
Converter Efficiency
for VOUT = 3.3V
100
90 VIN = 2.4V
80
70 VIN = 1.2V
VIN = 2.4V
60
VIN = 1.2V
50
40
30
20
10
0 TA = 25°C
0.1 1
Burst Mode OPERATION
1MHz/PHASE
10 100 1000 10000
OUTPUT CURRENT (mA)
3425 G11
Efficiency Comparison of
Discontinuous Mode and Forced
Continuous Mode at Light Loads
for VIN = 2.4V, VOUT = 3.3V
100
TA = 25°C
90 1MHz/PHASE
80 DISCONTINUOUS
MODE
70
60 FORCED
CONTINUOUS
50 MODE
40
30
20
10
0
1 10 100 1000
CONVERTER OUTPUT CURRENT (mA)
3425 G14
Oscillator Frequency
10
TA = 25°C
1
1 10 100
RT (kΩ)
3425 G17
Converter Efficiency
for VOUT = 5V
100
90 VIN = 3.3V
80 VIN = 2.4V
70
VIN = 3.3V VIN = 2.4V
60
50
40
30
20
10
0 TA = 25°C
0.1 1
Burst Mode OPERATION
1MHz/PHASE
10 100 1000 10000
OUTPUT CURRENT (mA)
3425 G12
Efficiency Comparison of
Discontinuous Mode and Forced
Continuous Mode at Light Loads
for VIN = 3.3V, VOUT = 5V
100
TA = 25°C
90 1MHz/PHASE
80
DISCONTINUOUS
70 MODE
60 FORCED
50 CONTINUOUS
MODE
40
30
20
10
0
1 10 100 1000
LOAD (mA)
3425 G15
Peak Current Limit
1.8
1.6
TA = 25°C
1.4
1.2
1.0
0.8
Converter Efficiency for 2-, 3- and
4-Phase Operation
98
TA = 25°C
96 VIN = 2.4V
VOUT = 3.3V
94 1MHz/PHASE
92
90
4 PHASE
88
86
2 PHASE 3 PHASE
84
82
80
100
1000
LOAD (mA)
10000
3425 G13
Converter No Load Input Current
vs VIN (Burst Mode Operation)
140
TA = 25°C
120
100
80 VOUT = 5V
60
VOUT = 3.3V
40
20
0
1.5 2.0
2.5 3.0 3.5
VIN (V)
Effective RDS(ON)
0.065
TA = 25°C
4.0 4.5
3425 G16
0.060
0.055
PMOS
0.050
0.045
NMOS
0.6 0.040
60 80 100 120 140 160 180 200
2.5 3 3.5 4 4.5 5
ILIM RESISTOR (kΩ)
VOUT (V)
3425 G18
3425 G19
3425f
5
5 Page 
U
OPERATIO
DETAILED DESCRIPTION
The LTC3425 provides high efficiency, low noise power
for high current boost applications such as cellular phones
and PDAs. The true output disconnect feature eliminates
inrush current and allows VOUT to go to zero during
shutdown. The current mode architecture with adaptive
slope compensation provides ease of loop compensation
with excellent transient load response. The low RDS(ON),
low gate charge synchronous switches eliminate the need
for an external Schottky rectifier, and provide efficient high
frequency pulse width modulation (PWM) control. High
efficiency is achieved at light loads when Burst Mode
operation is entered, where the IC’s quiescent current is a
low 12µA typical on VOUT.
MULTIPHASE OPERATION
The LTC3425 uses a 4-phase architecture, rather than the
conventional single phase of other boost converters. By
having multiple phases equally spaced (90° apart), not
only is the output ripple frequency increased by a factor of
four, but the output capacitor ripple current is greatly
reduced. Although this architecture requires four induc-
tors, rather than a single inductor, there are a number of
important advantages.
• Much lower peak inductor current allows the use of
smaller, lower cost inductors.
• Greatly reduced output ripple current minimizes output
capacitance requirement.
• Higher frequency output ripple is easier to filter for low
noise applications.
• Input ripple current is also reduced for lower noise on
VIN.
The peak boost inductor current is given by:
ILPEAK
=
IO
(1– D)
•N
+
di
2
Where IO is the average load current, D is the PWM duty
cycle, N is the number of phases and di is the inductor
ripple current. This relationship is shown graphically in
Figure 1 using a single phase and a 4-phase example.
LTC3425www.DataSheet4U.com
5
SINGLE
PHASE
4
3
FOUR PHASE
2
1
0
0 0.5 1 1.5
TIME (µs)
3425 F01
Figure 1. Comparison of Output Ripple Current with Single
Phase and 4-Phase Boost Converter in a 2A Load Application
Operating at 50% Duty Cycle
Example:
The following example, operating at 50% duty cycle,
illustrates the advantages of multiphase operation over a
conventional single-phase design.
VIN = 1.9V, VOUT = 3.6V, Efficiency = 90% (approx),
IOUT = 2A, Frequency = 1MHz, L = 2.2µH
Table 1
PARAMETER
SINGLE FOUR CHANGE FROM
PHASE PHASE 1 TO 4 PHASE
Peak-Peak Output
Ripple Current
4.227A 0.450A Reduced by 89%
RMS Output Ripple Current 2.00A 0.184A Reduced by 91%
Peak Inductor Current
4.227A 1.227A Reduced by 71%
Output Ripple Frequency
1MHz 4MHz Increased by 4×
With 4-phase operation, at least one of the phases will be
delivering current to the load whenever VIN is greater than
one quarter VOUT (duty cycles less than 75%). For lower
duty cycles, there can be as many as two or three phases
delivering load current simultaneously. This greatly re-
duces both the output ripple current and the peak current
in each inductor, compared with a single-phase converter.
This is illustrated in the waveforms of Figures 2 and 3.
Operation Using Only Two or Three Phases
The LTC3425 can operate as a 2- or 3-phase converter by
simply eliminating the inductor from the unused phase(s).
3425f
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11 Page | ||
| Páginas | Total 24 Páginas | |
| PDF Descargar | [ Datasheet LTC3425.PDF ] | |
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