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PDF LTC3421 Data sheet ( Hoja de datos )
| Número de pieza | LTC3421 | |
| Descripción | 3MHz Micropower Synchronous Boost Converter | |
| Fabricantes | Linear Technology | |
| Logotipo |  |
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LTC3421
3A, 3MHz Micropower
Synchronous Boost Converter
with Output Disconnect
FEATURES
s Synchronous Rectification: Up to 96% Efficiency
s True Output Disconnect
s Inrush Current Limiting
s Very Low Quiescent Current: 12µA
s Up to 1.5A Continuous Output Current
s Fixed Frequency Operation Up to 3MHz
s 0.5V to 4.5V Input Range
s 2.4V to 5.25V Adjustable Output Voltage
s Guaranteed 1V Start-Up
s Programmable Current Limit
s Programmable Soft-Start
s Synchronizable Oscillator
s Manual or Automatic Burst Mode® Operation
s Low-Battery Comparator
s < 1µA Shutdown Current
s 1.22V Reference Output Voltage
s Small (4mm × 4mm) Thermally Enhanced QFN
Package
U
APPLICATIO S
s Handheld Computers
s Cordless Phones
s GPS Receivers
s Battery Backup Supplies
DESCRIPTIO
The LTC®3421 is a high efficiency, current mode, fixed
frequency, step-up DC/DC converter with true output dis-
connect and inrush current limiting. The device includes a
0.10Ω N-channel MOSFET switch and a 0.14Ω P-channel
synchronous rectifier. This product has the ability to sim-
ply program the output voltage, switching frequency, cur-
rent limit, soft-start, Burst Mode threshold and loop
compensation with external passive components.
Quiescent current is only 12µA 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. An open-drain uncommitted low-battery com-
parator is included. The part maintains operation in
applications with a secondary cell powering the output
voltage during shutdown.
Other features include: 1µA shutdown, antiringing control,
thermal limit and reference output.
The LTC3421 is available in a small 4mm × 4mm 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
1.8V TO 3V
L1
4.7µH
2
CELLS
C1*
4.7µF
2
SHDN
4
ENB
3 VREF
23
LBI
22
LBO
7
SYNC
8
ILIM
45.3k
SS RT
21 14 15 16
VIN SW SW
LTC3421
SW
VOUTS
VOUT
VOUT
VOUT
FB
VC
BURST
18
17
19
20
1
24
9
GND PGND PGND PGND
65
10 11 12 13
0.1µF
28k
0.1µF
340k
VOUT
3.3V
1.2A
470pF
200k
C5*
22µF
20k 100k
*LOCATE COMPONENTS CLOSE TO PINS
C1: TAIYO YUDEN JMK212BJ106MM
C5: TAIYO YUDEN JMK325BJ226MM
L1: TDK RLF7030T-4R7M3R4
3421 TA01
2-Cell to 3.3V Efficiency
100
Burst Mode OPERATION
90
VIN = 3V
80
70
60
50
VIN = 2.4V
VIN = 2V
40
30
20
10 VOUT = 3.3V
fOSC = 1MHz
0
0.1 1 10 100
OUTPUT CURRENT (mA)
1000
3421 G02
3421f
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LTC3421
TYPICAL PERFOR A CE CHARACTERISTICS (TA = 25°C, unless otherwise specified)
Burst Mode Threshold vs RBURST
180
160
140
120
100
80
60
OUT OF BURST
40
20
0
20
INTO BURST
70
RBURST (kΩ)
120
3421 G10
Burst Mode Quiescent Current
20
15
10
5
0
–45 –30 –15 0 15 30 45 60 75 90
TEMPERATURE (°C)
3421 G13
FB Voltage
1.24
1.23
1.22
1.21
1.20
–45 –30 –15 0 15 30 45 60 75 90
TEMPERATURE (°C)
3421 G11
Current Limit Accuracy
1.70
RLIM = 105k
1.65
1.60
1.55
1.50
1.45
1.40
1.35
1.30
1.25
1.20
–45 –30 –15 0 15 30 45 60 75 90
TEMPERATURE (°C)
3421 G14
Frequency Accuracy
1.03
1.01
0.99
0.97
0.95
–45 –30 –15 0 15 30 45 60 75 90
TEMPERATURE (°C)
3421 G12
RDS(ON)
0.20
0.18
0.16
PMOS
0.14
0.12
NMOS
0.10
0.08
0.06
0.04
0.02
0
–45 –30 –15 0 15 30 45 60 75 90
TEMPERATURE (°C)
3421 G15
PI FU CTIO S
FB (Pin 1): Feedback Pin. Connect resistor divider tap
here. The output voltage can be adjusted from 2.4V to
5.25V. The feedback reference voltage is typically 1.220V.
SHDN (Pin 2): Shutdown Pin. Less than 0.25V on this pin
shuts down the IC. The IC is enabled when the SHDN
voltage is greater than 1V. Once VOUT is above 2.2V,
hysteresis is applied to the pin (–500nA out of the pin)
allowing it to operate at a logic high while the battery can
drop to 0.5V.
VREF (Pin 3): Buffered 1.22V Reference Output. This pin
can source up to 100µA and sink up to 8µA. This pin must
be decoupled with a 0.1µF capacitor for stability.
ENB (Pin 4): Reference Output (VREF) and Low-Battery
Comparator Enable. When ENB = Low, the VREF output and
low-battery comparator are disabled, which lowers the
quiescent current by 5µA. When ENB = High, the VREF
output and the low-battery comparator are enabled. Dur-
ing shutdown, if the ENB = High and the output voltage is
pulled up to greater than 2.5V from a secondary source
such as a coin cell through a Schottky diode, the VREF
output and low-battery comparator becomes powered
from the output voltage and enabled.
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OPERATIO
disconnect, there must not be any external Schottky
diodes connected between the SW pins and VOUT.
Note: Board layout is extremely critical to minimize volt-
age overshoot on the SW pins due to stray inductance.
Keep the output filter capacitors as close as possible to the
LTC3421
VOUT pins and use very low ESR/ESL ceramic capacitors,
tied to a good ground plane. In VOUT > 4.3V applications,
a Schottky diode is required from the switch nodes to VOUT
to limit the peak switch voltage to less than 6V unless
some form of external snubbing is employed. (See 5V
Applications section.)
APPLICATIO S I FOR ATIO
COMPONENT SELECTION
24
VC
1 FB
23 22 21 20 19
LBI LBO VIN VOUT VOUT
VOUTS 18
2 SHDN
VOUT 17
3 VREF
SW 16
4 ENB
SW 15
5 RT
SW 14
6 SS
PGND 13
SYNC ILIM BURST GND PGND PGND
7 8 9 10 11 12
VOUT
VIN
GND
MULTIPLE VIAS
TO GROUND
PLANE
3421 F01
Figure 1. Recommended Component Placement. Traces Carrying
High Current are Direct (PGND, SW, 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 IC
Pins as Possible
Inductor Selection
The high frequency operation of the LTC3421 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)
f f • 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 to 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 loses.
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 saturating. Molded
chokes or chip inductors usually do not have enough core
to support peak inductor currents in the 1A to 4A 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
Coiltronics (561) 241-7876 (516) 241-9339
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
3421f
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| Páginas | Total 16 Páginas | |
| PDF Descargar | [ Datasheet LTC3421.PDF ] | |
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