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PDF LTC3409 Data sheet ( Hoja de datos )
| Número de pieza | LTC3409 | |
| Descripción | 600mA Low Vin Buck Regulator | |
| Fabricantes | Linear Technology | |
| Logotipo |  |
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LTC3409
600mA Low VIN Buck
Regulator in 3mm × 3mm DFN
FEATURES
■ 1.6V to 5.5V Input Voltage Range
■ Internal Soft-Start
■ Selectable 1.7MHz or 2.6MHz Constant Frequency
Operation
■ Internal Oscillator can be Synchronizable to an
External Clock, 1MHz to 3MHz Range
■ High Efficiency: Up to 95%
■ Very Low Quiescent Current: Only 65µA During
Burst Mode® Operation
■ 600mA Output Current (VIN = 1.8V, VOUT = 1.2V)
■ 750mA Peak Inductor Current
■ No Schottky Diode Required
■ Low Dropout Operation: 100% Duty Cycle
■ 0.613V Reference Voltage
■ Stable with Ceramic Capacitors
■ Shutdown Mode Draws <1µA Supply Current
■ Current Mode Operation for Excellent Line and Load
Transient Response
■ Overtemperature Protection
■ Available in a Low Profile (0.75mm) 8-Lead
(3mm × 3mm) DFN Package
U
APPLICATIO S
■ Cellular Phones
■ Digital Cameras
■ MP3 Players
DESCRIPTIO
The LTC®3409 is a high efficiency, monolithic synchro-
nous buck regulator using a constant frequency, current
mode architecture. The output voltage is adjusted via an
external resistor divider.
Fixed switching frequencies of 1.7MHz and 2.6MHz are
supported. Alternatively, an internal PLL will synchronize
to an external clock in the frequency range of 1MHz to
3MHz. This range of switching frequencies allows the use
of small surface mount inductors and capacitors, includ-
ing ceramics.
Supply current during Burst Mode operation is only 65µA
dropping to <1µA in shutdown. The 1.6V to 5.5V input
voltage range makes the LTC3409 ideally suited for single
cell Li-Ion, Li-Metal and 2-cell alkaline, NiCd or NiMH
battery-powered applications. 100% duty cycle capability
provides low dropout operation, extending battery life in
portable systems. Burst Mode operation can be user-
enabled, increasing efficiency at light loads, further ex-
tending battery life.
The internal synchronous switch increases efficiency and
eliminates the need for an external Schottky diode. Inter-
nal soft-start offers controlled output voltage rise time at
start-up without the need for external components.
, LTC and LT 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.
Protected by U.S. Patents, including 5481178, 6580258, 6304066, 6127815,
6498466, 6611131.
TYPICAL APPLICATIO
High Efficiency Step-Down Converter
VIN
1.8V TO 5.5V
4.7µF
CER
LTC3409
VIN SW
RUN
MODE VFB
SYNC GND
2.2µH*
10pF
133k 255k
*SUMIDA CDRH2D18/LD
3409 TA01
VOUT
1.8V
10µF
CER
Burst Mode Efficiency, 1.8VOUT
100
90 2.5VIN, BURST
1.0
80
70
4.2VIN, BURST
0.1
60 3.6VIN, BURST
50 0
40
30
POWER LOST
3.6VIN, BURST
20
10
0
0.1 1 10 100 1000
LOAD CURRENT (mA)
3409 TA01b
3409f
1
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LTC3409
TYPICAL PERFOR A CE CHARACTERISTICS
(From Typical Application on the front page except for the resistive divider resistor values)
Oscillator Frequency
vs Temperature
2.70
2.60
2.50
2.40
2.30
2.20
2.10
2.00
1.90
1.80
1.70
1.60
1.50
1.40
1.30
1.20
–50
VIN = 2.7V
VIN = 1.6V
VIN = 4.2V OSC 2.6MHz
VIN = 4.2V
OSC 1.7MHz
VIN = 1.6V VIN = 2.7V
–25 0 25 50 75 100 125
TEMPERATURE (°C)
3409 G07
Oscillator Frequency Shift
vs Input Voltage
6
4 fLOW
1.7MHz
2
0
fHIGH
–2 2.6MHz
–4
–6
–8
–10
1.5
2.5 3.5 4.5
INPUT VOLTAGE (V)
5.5
3409 G08
Output Voltage vs Load Current
VIN = 1.6V
1.22
1.21
1.2VOUT
BURST
1.20
1.2VOUT
PULSE
SKIP
1.19
1.18
0 100 200 300 400 500 600 700 800 900
LOAD CURRENT (mA)
3409 G09
RDS(ON) vs Input Voltage
0.450
0.400
0.350
0.300
MAIN
SWITCH
0.250
0.200
0.150
SYNCHRONOUS
SWITCH
0.100
0.050
0
1.5 2.5 3.5 4.5
INPUT VOLTAGE (V)
5.5
3409 G10
RDS(ON) vs Input Temperature
0.55
MAIN SWITCH
0.50
1.6V
0.45
4.2V
0.40
2.7V 1.6V
0.35
0.30 2.7V
0.25
4.2V
0.20
0.15
0.10
–50 –25
SYNCHRONOUS SWITCH
0 25 50 75
TEMPERATURE (°C)
100 125
3409 G11
Dynamic Supply Current
vs Input Voltage
6000
5000
4000
BURST/SLEEP
VOUT = 1.5V
IOUT = 0
120
100
80
3000
VFB = VIN 60
2000
1000
PULSE
SKIP
VOUT = 1.5V
IOUT = 0
VFB = 0
40
20
00
1.5 2 2.5 3 3.5 4 4.5 5 5.5 6
INPUT VOLTAGE (V)
3409 G12
Dynamic Supply Current vs
Temperature, VIN = 3.6V,
VOUT = 1.5V, 0 Load
500
450
400
PULSE SKIP
350
300
250
200
150
100 BURST
50
0
–50 –25
0 25 50 75 100 125
TEMPERATURE (°C)
3409 G13
Switch Leakage vs Temperature
VIN = 5.5V
6000
VIN = 5.5V
5000
4000
3000
2000
1000
MAIN SWITCH
SYNCHRONOUS SWITCH
0
–50 –25
0 25 50 75
TEMPERATURE (°C)
100 125
3409 G14
Switch Leakage vs Input Voltage
45
40
35
30
25
MAIN SWITCH
20
15
10
SYNCHRONOUS
5 SWITCH
0
02468
INPUT VOLTAGE (V)
3409 G15
3409f
5
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LTC3409
APPLICATIO S I FOR ATIO
where f = operating frequency, COUT = output capacitance
and ∆IL = ripple current in the inductor. For a fixed output
voltage, the output ripple is highest at maximum input
voltage since ∆IL increases with input voltage. Aluminum
electrolytic and dry tantalum capacitors are both available
in surface mount configurations. In the case of tantalum,
it is critical that the capacitors are surge tested for use in
switching power supplies. An excellent choice is the AVX
TPS series of surface mount tantalum. These are specially
constructed and tested for low ESR so they give the lowest
ESR for a given volume. Other capacitor types include
Sanyo POSCAP, Kemet T510 and T495 series, and Sprague
593D and 595D series. Consult the manufacturer for other
specific recommendations.
Using Ceramic Input and Output Capacitors
Higher value, lower cost ceramic capacitors are now
available in smaller case sizes. Their high ripple current,
high voltage rating and low ESR make them ideal for
switching regulator applications. Because the LTC3409’s
control loop does not depend on the output capacitor’s
ESR for stable operation, ceramic capacitors can be used
to achieve very low output ripple and small circuit size.
However, care must be taken when these capacitors are
used at the input and the output. When a ceramic capacitor
is used at the input and the power is supplied by a wall
adapter through long wires, a load step at the output can
induce ringing at the input, VIN. At best, this ringing can
couple to the output and be mistaken as loop instability. At
worst, a sudden inrush of current through the long wires
can potentially cause a voltage spike at VIN, large enough
to damage the part.
When choosing the input and output ceramic capacitors,
choose the X5R or X7R dielectric formulations. These
dielectrics have the best temperature and voltage charac-
teristics of all the ceramics for a given value and size.
Output Voltage Programming
The output voltage is set by a resistive divider according
to the following formula:
VOUT = 0.613V⎛⎝⎜1+ RR21⎞⎠⎟
The external resistive divider is connected to the output,
allowing remote voltage sensing as shown in Figure 1.
VFB
LTC3409
GND
VOUT
R1
R2
3409 F01
Figure 1
Efficiency Considerations
The efficiency of a switching regulator is equal to the
output power divided by the input power times 100%. It is
often useful to analyze individual losses to determine what
is limiting the efficiency and which change would produce
the most improvement. Efficiency can be expressed as:
Efficiency = 100% – (L1 + L2 + L3 + ...)
where L1, L2, etc. are the individual losses as a percentage
of input power.
Although all dissipative elements in the circuit produce
losses, two main sources usually account for most of the
losses in LTC3409 circuits: VIN quiescent current and I2R
losses. The VIN quiescent current loss dominates the
efficiency loss at very low load currents whereas the I2R
loss dominates the efficiency loss at medium to high load
currents. In a typical efficiency plot, the efficiency curve at
very low load currents can be misleading since the actual
power lost is of no consequence as illustrated in Figure 2.
3409f
11
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| Páginas | Total 16 Páginas | |
| PDF Descargar | [ Datasheet LTC3409.PDF ] | |
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