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PDF LTC3409A Data sheet ( Hoja de datos )
| Número de pieza | LTC3409A | |
| Descripción | 600mA Low VIN Buck Regulator | |
| Fabricantes | Linear Technology Corporation | |
| Logotipo |  |
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LTC3409A
600mA Low VIN Buck
Regulator in 3mm × 3mm DFN
FEATURES
n 1.6V to 5.5V Input Voltage Range
n 0.62V to 5.5V Output Voltage Range
n Internal Soft-Start
n Selectable 1.7MHz or 2.6MHz Constant Frequency
Operation
n Internal Oscillator Can Be Synchronized to an
External Clock, 1MHz to 3MHz Range
n High Efficiency: Up to 95%
n 65μA Quiescent Current, Burst Mode® Operation
n 600mA Output Current (VIN = 1.8V, VOUT = 1.2V)
n 750mA Peak Inductor Current
n No Schottky Diode Required
n Low Dropout Operation: 100% Duty Cycle
n 0.612V Reference Voltage
n Stable with Ceramic Capacitors
n Shutdown Mode Draws <1μA Supply Current
n Current Mode Operation for Excellent Line and Load
Transient Response
n Overtemperature Protection
n Available in a Low Profile (0.75mm)
8-Lead (3mm × 3mm) DFN Package
APPLICATIONS
n Cellular Phones
n Digital Cameras
n MP3 Players
DESCRIPTION
The LTC®3409A is a high efficiency, monolithic synchronous
buck regulator using a constant frequency, current mode
architecture. The LTC3409A improves upon the LTC3409’s
light load regulation in Burst Mode operation. 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,
including 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 LTC3409A 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 bat-
tery life in portable systems. Burst Mode operation can be
user-enabled, increasing efficiency at light loads, further
extending battery life.
The internal synchronous switch increases efficiency and
eliminates the need for an external Schottky diode. Internal
soft-start offers controlled output voltage rise time at start-
up without the need for external components.
L, LT, LTC, LTM, Linear Technology and the Linear logo 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, 6304066, 6127815, 6498466, 6611131.
TYPICAL APPLICATION
High Efficiency Step-Down Converter
VIN
1.8V TO 5.5V
4.7μF
LTC3409A
VIN SW
RUN
MODE VFB
SYNC GND
2.2μH*
10pF
267k
137k
*SUMIDA CDRH2D18/LD
VOUT
1.8V
22μF
s2
3409A TA01
Burst Mode Efficiency, 1.8VOUT
100 1
90 2.5VIN, BURST
80
70
60 3.6VIN, BURST
0.1
50 0.01
40 4.2VIN, BURST
POWER LOST
30 3.6VIN, BURST
0.001
20
10
0 0.0001
0 1 10 100 1000
LOAD CURRENT (mA)
3409A TA01b
3409af
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LTC3409A
TYPICAL PERFORMANCE CHARACTERISTICS
(TA = 25°C, from Typical Application on the front page except for the resistive divider resistor values)
Output Voltage
vs Load Current VIN = 1.6V
1.210
RDS(ON) vs Input Voltage
0.45
RDS(ON) vs Temperature
0.55
1.205
1.200
1.195
1.190
1.185
1.100
1
1.2VOUT, BURST
1.2VOUT, PULSE-SKIPPING
10 100
LOAD CURRENT (mA)
1000
3409A G09
0.40
0.35
0.30
0.25
0.20
0.15
0.10
0.05
0
1.5
MAIN
SWITCH
SYNCHRONOUS
SWITCH
2.5 3.5 4.5
INPUT VOLTAGE (V)
5.5
3409A G10
0.50
0.45
0.40
0.35
0.30
0.25
0.20
0.15
0.10
–50 –25
1.6VIN
4.2VIN
2.7VIN
1.6VIN
2.7VIN
4.2VIN
MAIN SWITCH
SYNCHRONOUS SWITCH
0 25 50 75
TEMPERATURE (°C)
100 125
3409A G11
Dynamic Input Current
vs Input Voltage
3500
3000
2500
BURST
VOUT = 1.5V
IOUT = 0
VFB = 1V
2000
90
80
70
60
50
1500
1000
500
0
1.5
40
VOUT = 1.5V
IOUT = 0
PULSE-SKIPPING
30
20
10
VFB = 1V
0
2.5 3.5 4.5 5.5
INPUT VOLTAGE (V)
3409A G12
Dynamic Supply Current
vs Temperature, VIN = 3.6V,
VOUT = 1.5V, No Load
500
450
400 PULSE-SKIPPING
350
300
250
200
150
100 BURST
50
0
–50 –25
0 25 50 75
TEMPERATURE (°C)
100 125
3409A G13
Switch Leakage
vs Temperature VIN = 5.5V
6000
5000
4000
3000
2000
1000
MAIN SWITCH
SYNCHRONOUS SWITCH
0
–50 –25
0 25 50 75
TEMPERATURE (°C)
100 125
3409A G14
Switch Leakage vs Input Voltage
45
40
35
30
25
MAIN SWITCH
20
15
10
SYNCHRONOUS
5 SWITCH
0
0246
INPUT VOLTAGE (V)
3409A G15
3409af
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LTC3409A
APPLICATIONS INFORMATION
The output ripple ΔVOUT is determined by:
ΔVOUT
=
ΔIL
⎛
⎝⎜
ESR
+
8
•
f
1
• COUT
⎞
⎠⎟
where f = operating frequency, COUT = output capacitance
and ΔIL = ripple current in the inductor. For a fixed output
voltage, the output ripple is highest at maximum input
voltage since ΔIL 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 avail-
able in smaller case sizes. Their high ripple current, high
voltage rating and low ESR make them ideal for switching
regulator applications. Because the LTC3409A’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 Equation 2:
VOUT
=
0.612V
⎛
⎝⎜
1+
R1⎞
R2 ⎠⎟
(2)
The external resistive divider is connected to the output,
allowing remote voltage sensing as shown in Figure 1.
VFB
LTC3409A
GND
VOUT
R1
R2
3409A 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 percent-
age of input power.
Although all dissipative elements in the circuit produce
losses, two main sources usually account for most of
the losses in LTC3409A 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.
3409af
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11 Page | ||
| Páginas | Total 16 Páginas | |
| PDF Descargar | [ Datasheet LTC3409A.PDF ] | |
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