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PDF LTC3422 Data sheet ( Hoja de datos )
| Número de pieza | LTC3422 | |
| Descripción | 3MHz Synchronous Step-Up DC/DC Converter | |
| Fabricantes | Linear Technology | |
| Logotipo |  |
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LTC3422
1.5A, 3MHz Synchronous
Step-Up DC/DC Converter
with Output Disconnect
FEATURES
■ 700mA Continuous/1A Pulsed Output Current
for Li-Ion to 5V Applications
■ Synchronous Rectification: Up to 96% Efficiency
■ True Output Disconnect
■ Inrush Current Limiting
■ Adjustable Automatic Burst Mode® Operation
■ Low Noise, Fixed Frequency Operation from
100kHz to 3MHz
■ 0.5V to 4.5V Input Range
■ 2.25V to 5.25V Adjustable Output Voltage
■ Guaranteed 1V Start-Up
■ Programmable Soft-Start
■ Synchronizable Oscillator
■ Low Quiescent Current: 25µA
■ < 1µA Shutdown Current
■ Anti-Ringing Control
■ Small (3mm × 3mm × 0.75mm) Thermally Enhanced
10-Pin DFN Package
U
APPLICATIO S
■ Wireless Handsets
■ Handheld Computers
■ GPS Receivers
■ MP3 Players
DESCRIPTIO
The LTC®3422 is a high efficiency, current mode, fixed
frequency, step-up DC/DC converter with true output
disconnect and inrush current limiting. The part is guaran-
teed to start up from an input voltage of 1V. The device
includes a 0.20Ω N-channel MOSFET switch and a 0.24Ω
P-channel MOSFET synchronous rectifier. The output
voltage, switching frequency, soft-start time, Burst Mode
threshold and loop compensation are all simply pro-
grammed using tiny external passive components.
Quiescent current is only 25µA during Burst Mode opera-
tion, maximizing battery life in portable applications. The
oscillator frequency can be programmed up to 3MHz and
can be synchronized to an external clock applied to the
SYNC pin.
Other features include 1µA shutdown, short-circuit protec-
tion, anti-ringing control, thermal shutdown and current
limit.TheLTC3422isavailableina(3mm× 3mm ×0.75mm)
10-pin DFN package.
, LT, LTC and LTM are registered trademarks of Linear Technology Corporation.
Burst Mode is a registered trademark of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
TYPICAL APPLICATIO
VIN
1.8V TO 3.2V
+
2 CELLS
4.7µF
4.7µH
VIN SW
SYNC
VOUT
LTC3422
OFF ON
SHDN
FB
VC BURST
1nF SS RT GND
15k
22pF
0.1µF 28k
22µF
VOUT
3.3V
600mA
931k
549k
2.2nF 301k
3422 TA01a
2.4V to 3.3V Efficiency and Power Loss
100
BURST
90 EFFICIENCY
80
10000
1000
70 PWM
EFFICIENCY
60 100
50
40
30
20
10
0
0.1
PWM
10
POWER
LOSSES
BURST
1
POWER
LOSSES
fOSC = 1MHz 0
1 10 100 1000
LOAD CURRENT (mA)
3422 TA01b
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LTC3422
TYPICAL PERFOR A CE CHARACTERISTICS (TA = 25°C, unless otherwise specified)
Burst Mode Output Current
Threshold vs RBURST (3.3V Output)
140 VIN = 1.25V TO 2.9V
VOUT = 3.3V
120 fOSC = 1MHz
100
80
60
ENTERS BURST (MIN)
40
EXITS BURST (AVE)
20
0
50 150 250 350 450 550 650 750 850
RBURST (kΩ)
3422 G10
Burst Mode Output Current
Threshold vs RBURST (5V Output)
140 VIN = 1.8V TO 4.2V
VOUT = 5V
120 fOSC = 1MHz
100
80
ENTERS BURST (MIN)
60
40 EXITS BURST (AVE)
20
0
50 125 200 275 350 425 500 575 650
RBURST (kΩ)
3422 G11
FB Voltage vs Temperature
1.217
1.216
1.215
1.214
1.213
–45 –30 –15 0 15 30 45 60 75 90
TEMPERATURE (°C)
3422 G12
Frequency vs Temperature
(Normalized About 1MHz)
1.02
Burst Mode Quiescent Current
vs Temperature
30
Current Limit vs Temperature
2.55
1.01 28 2.50
1.00 26 2.45
0.99 24 2.40
0.98
–45 –30 –15 0 15 30 45 60 75 90
TEMPERATURE (°C)
3422 G13
RDS(ON) vs Temperature
280
260
PMOS RDS(ON)
240
220
NMOS RDS(ON)
200
180
160
–45 –30 –15 0 15 30 45 60 75 90
TEMPERATURE (°C)
3422 G16
22
–45 –30 –15 0 15 30 45 60 75 90
TEMPERATURE (°C)
3422 G14
No-Load Input Current vs VIN
170
160
150
140
130
120
110
100
90
80
70
60
50
0.8 1.2 1.6
CHIP ENTERS
Burst Mode OPERATION
VOUT = 5V
VOUT = 3.3V
2 2.4 2.8 3.2 3.6 4 4.4 4.8
INPUT VOLTAGE (V)
3422 G17
2.35
–45 –30 –15 0 15 30 45 60 75 90
TEMPERATURE (°C)
3422 G15
Maximum Output Current vs VIN
2000
fOSC = 1MHz
1800
1600 VOUT = 3.3V VOUT = 5V
1400
1200
1000
800
5V DIODE
RECTIFICATION
3.3V DIODE
RECTIFICATION
600
400
1.80 2.40 3.00 3.60 4.20 4.80 5.40
INPUT VOLTAGE (V)
3422 G18
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OPERATIO
the input source. It also allows for inrush current limiting
at turn-on, minimizing surge currents seen by the input
supply. Note that to obtain the advantages of output
disconnect, there must not be any external Schottky
diodes connected between the SW pin and VOUT.
LTC3422
It should also be noted that the LTC3422 provides inrush
current limiting without reducing the maximum load cur-
rent capability during start-up. The internally set peak
current command of the LTC3422 is allowed to gradually
increase during the soft-start period until it reaches the
nominal maximum level.
APPLICATIO S I FOR ATIO
Note: Board layout is extremely critical to minimize voltage
overshoot on SW due to stray inductance. Keep the output
filter capacitors as close as possible to VOUT and use very
low ESR/ESL ceramic capacitors tied to a good ground
plane.
VOUT
LTC3422
VIN
1 SW
VOUT 10
2 VIN
SYNC 9
3 BURST
RT 8
4 SS
VC 7
5 SHDN
FB 6
MULTIPLE VIAS
TO GROUND PLANE
3422 F01
Figure 1. Recommended Component Placement. Traces
Carrying High Current are Direct (GND, SW, VIN, VOUT). Trace
Area at FB and VC are Kept Low. Lead Length to Battery Should
be Kept Short. VIN and VOUT Ceramic Capacitors Should be as
Close to the LTC3422 Pins as Possible
COMPONENT SELECTION
Inductor Selection
The high frequency operation of the LTC3422 allows the
use of small surface mount inductors. The minimum
inductance value is proportional to the operating fre-
quency and is limited by the following constraints:
( )L > 3 and L > VIN(MIN) • VOUT(MAX) – VIN(MIN)
ƒ ƒ • Ripple • VOUT(MAX)
where:
f = Operating Frequency in MHz
Ripple = Allowable Inductor Current Ripple (Amps
Peak-Peak)
VIN(MIN) = Minimum Input Voltage
VOUT(MAX) = Maximum Output Voltage
The inductor current ripple is typically set 20% to 40% of
the maximum inductor current.
For high efficiency, choose an inductor with high fre-
quency core material, such as ferrite, to reduce core
losses. The inductor should have low ESR (equivalent
series resistance) to reduce the I2R losses and must be
able to handle the peak inductor current without saturat-
ing. Molded chokes or chip inductors usually do not have
enough core to support peak inductor currents in the 2A
to 3A region. To minimize radiated noise, use a toroidal or
shielded inductor. See Table 1 for suggested inductor
suppliers and Table 2 for a list of capacitor suppliers.
Table 1. Inductor Vendor Information
SUPPLIER PHONE
FAX
WEB SITE
Coilcraft (847) 639-6400 (847) 639-1469 www.coilcraft.com
CoEv (800) 277-7040 (650) 361-2508 www.circuitprotection.
Magnetics
com/magnetics.asp
Murata
USA: USA: www.murata.com
(814) 237-1431 (814) 238-0490
(800) 831-9172
Sumida
USA: USA: www.sumida.com
(847) 956-0666 (847) 956-0702
Japan:
Japan:
81-3-3607-5111 81-3-3607-5144
TDK (847) 803-6100 (847) 803-6296 www.component.tdk.com
TOKO (847) 297-0070 (847) 669-7864 www.toko.com
Wurth (201) 785-8800 (201) 785-8810 www.we-online.com
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11 Page | ||
| Páginas | Total 16 Páginas | |
| PDF Descargar | [ Datasheet LTC3422.PDF ] | |
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