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PDF LT3470 Data sheet ( Hoja de datos )
| Número de pieza | LT3470 | |
| Descripción | Micropower Buck Regulator | |
| Fabricantes | Linear Integrated Systems | |
| Logotipo |  |
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LT3470www.DataSheet4U.com
Micropower Buck Regulator
with Integrated Boost and
Catch Diodes
FEATURES
■ Low Quiescent Current: 26µA at 12VIN to 3.3VOUT
■ Integrated Boost and Catch Diodes
■ Input Range: 4V to 40V
■ Low Output Ripple: <10mV
■ < 1µA in Shutdown Mode
■ Output Voltage: 1.25V to 16V
■ 200mA Output Current
■ Hysteretic Mode Control
– Low Ripple Burst Mode® Operation at Light Loads
– Continuous Operation at Higher Loads
■ Solution Size as Small as 50mm2
■ Low Profile (1mm) ThinSOT Package
U
APPLICATIO S
■ Automotive Battery Regulation
■ Power for Portable Products
■ Distributed Supply Regulation
■ Industrial Supplies
■ Wall Transformer Regulation
DESCRIPTIO
The LT®3470 is a micropower step-down DC/DC converter
that integrates a 300mA power switch, catch diode and
boost diode into a low profile (1mm) ThinSOTTM package.
The LT3470 combines Burst Mode and continuous opera-
tion to allow the use of tiny inductor and capacitors while
providing a low ripple output to loads of up to 200mA.
With its wide input range of 4V to 40V, the LT3470 can
regulate a wide variety of power sources, from 2-cell
Li-Ion batteries to unregulated wall transformers and lead-
acid batteries. Quiescent current in regulation is just 26µA
in a typical application while a zero current shutdown
mode disconnects the load from the input source, simpli-
fying power management in battery-powered systems.
Fast current limiting and hysteretic control protects the
LT3470 and external components against shorted out-
puts, even at 40V input.
, LTC and LT are registered trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
Burst Mode is a registered trademark of Linear Technology Corporation.
ThinSOT is a trademark of Linear Technology Corporation.
TYPICAL APPLICATIO
VIN
7V TO 40V
OFF ON
VIN BOOST
LT3470
SHDN
SW
BIAS
2.2µF
FB
GND
0.22µF
33µH
22pF
604k
1%
200k
1%
VOUT
5V
200mA
22µF
Efficiency and Power Loss vs Load Current
90
VIN = 12V
80
1000
70 100
60
50 10
40
30 1
20
10
0.1
1 10
LOAD CURRENT (mA)
0.1
100
3470 TA02
3470f
1
1 page  
TYPICAL PERFOR A CE CHARACTERISTICS
LT3470www.DataSheet4U.com
Diode Leakage (VR = 36V)
vs Temperature
25
BOOST
CATCH
20
15
Switch VCESAT
700
600
500
400
BOOST Pin Current
14
12
10
8
10 300
200
5
100
6
4
2
0
–50 –25
0 25 50 75
TEMPERATURE (°C)
100 125
3470 G13
0
0 100 200 300 400
SWITCH CURRENT (mA)
3470 G14
0
0 100 200 300 400
SWITCH CURRENT (mA)
3470 G15
Catch Diode Forward Voltage
1.0
0.8
0.6
0.4
0.2
0
0 100 200 300 400
CATCH DIODE CURRENT (mA)
3470 G16
Boost Diode Forward Voltage
900
800
700
600
500
400
300
200
100
0
0 50 100 150 200
BOOST DIODE CURRENT (mA)
3470 G17
Minimum Input Voltage, VOUT = 3.3V
6.0
TA = 25°C
VIN TO START
5.5
5.0
Minimum Input Voltage, VOUT = 5V
8
TA = 25°C
VIN TO START
7
4.5
4.0
VIN TO RUN
3.5
6
VIN TO RUN
5
3.0
0
50 100 150
LOAD CURRENT (mA)
200
3470 G18
4
0 50 100 150 200
LOAD CURRENT (mA)
3470 G19
3470f
5
5 Page 
LT3470www.DataSheet4U.com
APPLICATIO S I FOR ATIO
(Figure 2b). The circuit in Figure 2a is more efficient
because the BOOST pin current and BIAS pin quiescent
current comes from a lower voltage source. You must also
be sure that the maximum voltage ratings of the BOOST
and BIAS pins are not exceeded.
The minimum operating voltage of an LT3470 application
is limited by the undervoltage lockout (4V) and by the
maximum duty cycle as outlined in a previous section. For
proper start-up, the minimum input voltage is also limited
by the boost circuit. If the input voltage is ramped slowly,
or the LT3470 is turned on with its SHDN pin when the
output is already in regulation, then the boost capacitor
may not be fully charged. The plots in Figure 3 show
Minimum Input Voltage, VOUT = 3.3V
6.0
TA = 25°C
5.5
VIN TO START
5.0
4.5
4.0
VIN TO RUN
3.5
3.0
0
50 100 150
LOAD CURRENT (mA)
200
3470 G18
Minimum Input Voltage, VOUT = 5V
8
TA = 25°C
VIN TO START
7
6
VIN TO RUN
5
4
0 50 100 150 200
LOAD CURRENT (mA)
3470 G19
Figure 3. The Minimum Input Voltage Depends on Output
Voltage, Load Current and Boost Circuit
minimum VIN to start and to run. At light loads, the
inductor current becomes discontinuous and the effective
duty cycle can be very high. This reduces the minimum
input voltage to approximately 300mV above VOUT. At
higher load currents, the inductor current is continuous
and the duty cycle is limited by the maximum duty cycle of
the LT3470, requiring a higher input voltage to maintain
regulation.
Shorted Input Protection
If the inductor is chosen so that it won’t saturate exces-
sively at the top switch current limit maximum of 450µA,
an LT3470 buck regulator will tolerate a shorted output
even if VIN = 40V. There is another situation to consider in
systems where the output will be held high when the input
to the LT3470 is absent. This may occur in battery charg-
ing applications or in battery backup systems where a
battery or some other supply is diode OR-ed with the
LT3470’s output. If the VIN pin is allowed to float and the
SHDN pin is held high (either by a logic signal or because
it is tied to VIN), then the LT3470’s internal circuitry will
pull its quiescent current through its SW pin. This is fine
if your system can tolerate a few mA in this state. If you
ground the SHDN pin, the SW pin current will drop to
essentially zero. However, if the VIN pin is grounded while
the output is held high, then parasitic diodes inside the
LT3470 can pull large currents from the output through
the SW pin and the VIN pin. Figure 4 shows a circuit that
will run only when the input voltage is present and that
protects against a shorted or reversed input.
D1
VIN
36
100k
VIN BOOST
LT3470 SOT-23
15
SHDN
SW
BIAS 7
1M FB 8
GND
4
VOUT
BACKUP
3470 F04
Figure 4. Diode D1 Prevents a Shorted Input from Discharging a
Backup Battery Tied to the Output; It Also Protects the Circuit
from a Reversed Input. The LT3470 Runs Only When the Input is
Present Hot Plugging Safely
3470f
11
11 Page | ||
| Páginas | Total 16 Páginas | |
| PDF Descargar | [ Datasheet LT3470.PDF ] | |
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