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PDF LTC3411A Data sheet ( Hoja de datos )
| Número de pieza | LTC3411A | |
| Descripción | 1.25A/ 4MHz/ Synchronous Step-Down DC/DC Converter | |
| Fabricantes | Linear Technology | |
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LTC3411Awww.DataSheet4U.com
1.25A, 4MHz, Synchronous
Step-Down DC/DC Converter
FEATURES
■ Uses Tiny Capacitors and Inductor
■ High Frequency Operation: Up to 4MHz
■ Low RDS(ON) Internal Switches: 0.15Ω
■ High Efficiency: Up to 96%
■ Selectable Low Ripple (25mVP-P) Burst Mode®
Operation: IQ = 40μA
■ Stable with Ceramic Capacitors
■ Current Mode Operation for Excellent Line
and Load Transient Response
■ Short-Circuit Protected
■ Low Dropout Operation: 100% Duty Cycle
■ Low Shutdown Current: IQ ≤ 1μA
■ Output Voltages from 0.8V to 5V
■ Synchronizable to External Clock
■ Supports Pre-Biased Outputs
■ Small 10-Lead 3mm × 3mm DFN or MSOP Package
APPLICATIONS
■ Notebook Computers
■ Digital Cameras
■ Cellular Phones
■ Handheld Instruments
■ Board Mounted Power Supplies
DESCRIPTION
The LTC®3411A is a constant frequency, synchronous
step-down DC/DC converter. Intended for medium power
applications, it operates from a 2.5V to 5.5V input voltage
range and has a user configurable operating frequency
up to 4MHz, allowing the use of tiny, low cost capacitors
and inductors 1mm or less in height. The output voltage is
adjustable from 0.8V to 5.5V. Internal synchronous power
switches provide high efficiency. The LTC3411A’s current
mode architecture and external compensation allow the
transient response to be optimized over a wide range of
loads and output capacitors.
The LTC3411A can be configured for automatic power
saving Burst Mode operation (IQ = 40μA) to reduce gate
charge losses when the load current drops below the level
required for continuous operation. For reduced noise and
RF interference, the SYNC/MODE pin can be configured to
skip pulses or provide forced continuous operation.
To further maximize battery life, the P-channel MOSFET
is turned on continuously in dropout (100% duty cycle).
In shutdown, the device draws <1μA.
L, LT, LTC, LTM and Burst Mode 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, 6498466, 6611131.
TYPICAL APPLICATION
Step-Down 2.5V/1.25A Regulator
VIN
2.5V TO 5.5V
SYNC
SYNC/MODE
PGOOD
LTC3411A
PVIN
SVIN
SW
10μF
2.2μH
22pF
VOUT
2.5V
1.25A
12.1k
680pF
ITH
SHDN/RT
SGND
549k
VFB
PGND
887k
412k
3411a TA01a
22μF
Efficiency and Power Loss vs Output Current
100 1
90
80
0.1
70
60
50 0.01
40
30
0.001
20 VIN = 2.7V
VIN = 3.6V
10 VIN = 4.2V
0 0.0001
0.1 1 10 100 1000 10000
OUTPUT CURRENT (mA)
fO = 1MHz
Burst Mode OPERATION
3411A TA01b
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LTC3411Awww.DataSheet4U.com
TYPICAL PERFORMANCE CHARACTERISTICS TA = 25°C, VIN = 3.6V, fO = 1MHz, unless
otherwise noted.
Frequency Variation vs VIN
6
4
2
0
–2
–4
–6
–8
2.5 3.0 3.5 4.0 4.5 5.0 5.5
VIN (V)
3411A G10
Dynamic Supply Current vs Input
Voltage
100
10 FORCED CONTINUOUS
1
PULSE SKIP
0.1 Burst Mode
OPERATION
0.01
VOUT = 1.8V
ILOAD = 0A
0.001
2.5 3.0 3.5 4.0 4.5 5.0 5.5
VIN (V)
3411A G13
RDS(ON) vs Input Voltage
0.25
0.20
0.15
0.10
0.05
MAIN SWITCH
SYNCHRONOUS SWITCH
0.0
2.5 3.0 3.5 4.0 4.5 5.0 5.5
INPUT VOLTAGE (V)
3411A G11
Dynamic Supply Current vs
Temperature
100
10 FORCED CONTINUOUS
1
PULSE SKIP
0.1 Burst Mode
OPERATION
0.01
0.001
–50 –25
VOUT = 1.8V
ILOAD = 0A
0 25 50 75
TEMPERATURE (°C)
100 125
3411A G14
RDS(ON) vs Temperature
0.30
0.25
0.20
0.15
0.10
0.05
0.0
–50 –25
MAIN SWITCH
SYNCHRONOUS SWITCH
0 25 50 75
TEMPERATURE (°C)
100 125
3411A G12
Switch Leakage vs Input Voltage
2500
2000
1500
MAIN SWITCH
1000
SYNCHRONOUS SWITCH
500
0
012 345 6
INPUT VOLTAGE(V)
3411A G15
Switch Leakage vs Temperature
600
500
Burst Mode Operation
SW
2V/DIV
400 VOUT
50mV/DIV
300 AC COUPLED
200
100
0
–50
MAIN SWITCH
SYNCHRONOUS SWITCH
–25 0 25 50 75 100 125
TEMPERATURE (°C)
3411A G16
IL
200mA/DIV
VIN = 3.6V
VOUT = 1.8V
ILOAD = 50mA
4μs/DIV
Pulse Skippng Mode
SW
2V/DIV
VOUT
50mV/DIV
AC COUPLED
IL
200mA/DIV
3411A G17
VIN = 3.6V
VOUT = 1.8V
ILOAD = 5mA
4μs/DIV
3411A G18
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LTC3411Awww.DataSheet4U.com
APPLICATIONS INFORMATION
shows some typical surface mount inductors that work
well in LTC3411A applications.
Table 1. Representative Surface Mount Inductors
MANU-
FACTURER PART NUMBER
MA X DC
VALUE CURRENT DCR HEIGHT
Toko A914BYW-1R2M=P3: 1.2μH 2.15A 44mΩ 2mm
D52LC
A960AW-1R2M=P3:
D518LC
1.2μH 1.8A 46mΩ 1.8mm
DB3015C-1068AS-1R0N 1.0μH 2.1A 43mΩ 1.5mm
DB3018C-1069AS-1R0N 1.0μH 2.1A 45mΩ 1.8mm
DB3020C-1070AS-1R0N 1.0μH 2.1A 47mΩ 2mm
A914BYW-2R2M-D52LC 2.2μH 2.05A 49mΩ 2mm
A915AY-2ROM-D53LC 2.0μH 3.3A 22mΩ 3mm
Coilcraft LPO1704-122ML
1.2μH 2.1A 80mΩ 1mm
D01608C-222
2.2μH 2.3A 70mΩ 3mm
LP01704-222M
2.2μH 2.4A 120mΩ 1mm
Sumida CR32-1R0
1.0μH 2.1A 72mΩ 3mm
CR5D11-1R0
1.0μH 2.2A 40mΩ 1.2mm
CDRH3D14-1R2
1.2μH 2.2A 36mΩ 1.5mm
CDRH4D18C/LD-1R1 1.1μH 2.1A 24mΩ 2mm
CDRH4D28C/LD-1R0 1.0μH 3.0A 17.5mΩ 3mm
CDRH4D28C-1R1
1.1μH 3.8A 22mΩ 3mm
CDRH4D28-1R2
1.2μH 2.56A 23.6mΩ 3mm
CDRH6D12-1R0
1.0μH 2.80A 37.5mΩ 1.5mm
CDRH4D282R2
2.2μH 2.04A 23mΩ 3mm
CDC5D232R2
2.2μH 2.16A 30mΩ 2.5mm
TaiyoYuden NPO3SB1ROM
1.0μH 2.6A 27mΩ 1.8mm
N06DB2R2M
2.2μH 3.2A 29mΩ 3.2mm
N05DB2R2M
2.2μH 2.9A 32mΩ 2.8mm
Murata LQN6C2R2M04
2.2μH 3.2A 24mΩ 5mm
FDK MIPW3226DORGM 0.9μH 1.4A 80mΩ 1mm
Catch Diode Selection
Although unnecessary in most applications, a small
improvement in efficiency can be obtained in a few ap-
plications by including the optional diode D1 shown in
Figure 4, which conducts when the synchronous switch
is off. When using Burst Mode operation or pulse skip
mode, the synchronous switch is turned off at a low
current and the remaining current will be carried by the
optional diode. It is important to adequately specify the
diode peak current and average power dissipation so as
not to exceed the diode ratings. The main problem with
Schottky diodes is that their parasitic capacitance reduces
the efficiency, usually negating the possible benefits for
LTC3411A circuits. Another problem that a Schottky diode
can introduce is higher leakage current at high tempera-
tures, which could reduce the low current efficiency.
Remember to keep lead lengths short and observe proper
grounding (see Board Layout Considerations) to avoid ring-
ing and increased dissipation when using a catch diode.
Input Capacitor (CIN) Selection
In continuous mode, the input current of the converter is a
square wave with a duty cycle of approximately VOUT/VIN.
To prevent large voltage transients, a low equivalent series
resistance (ESR) input capacitor sized for the maximum
RMS current must be used. The maximum RMS capacitor
current is given by:
IRMS ≈ IMAX
VOUT (VIN − VOUT )
VIN
where the maximum average output current IMAX equals
the peak current minus half the peak-to-peak ripple cur-
rent, IMAX = ILIM – ΔIL/2.
This formula has a maximum at VIN = 2VOUT, where
IRMS ≅ IOUT/2. This simple worst case is commonly used
to design because even significant deviations do not offer
much relief. Note that capacitor manufacturer’s ripple cur-
rent ratings are often based on only 2000 hours lifetime.
This makes it advisable to further derate the capacitor,
or choose a capacitor rated at a higher temperature than
required. Several capacitors may also be paralleled to meet
the size or height requirements of the design. An additional
0.1μF to 1μF ceramic capacitor is also recommended on
VIN for high frequency decoupling, when not using an all
ceramic capacitor solution.
Output Capacitor (COUT) Selection
The selection of COUT is driven by the required ESR to
minimize voltage ripple and load step transients. Typically,
once the ESR requirement is satisfied, the capacitance
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11 Page | ||
| Páginas | Total 20 Páginas | |
| PDF Descargar | [ Datasheet LTC3411A.PDF ] | |
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