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PDF LT1913 Data sheet ( Hoja de datos )
| Número de pieza | LT1913 | |
| Descripción | Step-Down Switching Regulator | |
| Fabricantes | Linear | |
| Logotipo |  |
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LT1913
25V, 3.5A, 2.4MHz
Step-Down Switching Regulator
FEATURES
■ Wide Input Range: 3.6V to 25V
■ 3.5A Maximum Output Current
■ Adjustable Switching Frequency: 200kHz to 2.4MHz
■ Low Shutdown Current: IQ < 1μA
■ Integrated Boost Diode
■ Synchronizable Between 250kHz to 2MHz
■ Power Good Flag
■ Saturating Switch Design: 95m On-Resistance
■ 0.790V Feedback Reference Voltage
■ Output Voltage: 0.79V to 25V
■ Thermal Protection
■ Soft-Start Capability
■ Small 10-Pin (3mm × 3mm) DFN Packages
U
APPLICATIO S
■ Automotive Battery Regulation
■ Power for Portable Products
■ Distributed Supply Regulation
■ Industrial Supplies
■ Wall Transformer Regulation
DESCRIPTIO
The LT®1913 is an adjustable frequency (200kHz to
2.4MHz) monolithic buck switching regulator that accepts
input voltages up to 25V. A high efficiency 95m switch
is included on the die along with a boost Schottky diode
and the necessary oscillator, control, and logic circuitry.
Current mode topology is used for fast transient response
and good loop stability. Shutdown reduces input supply
current to less than 1μA while a resistor and capacitor on
the RUN/SS pin provide a controlled output voltage ramp
(soft-start). A power good flag signals when VOUT reaches
91% of the programmed output voltage. The LT1913 is
available in 10-Pin 3mm × 3mm DFN packages with ex-
posed pads for low thermal resistance.
, LT, LTC and LTM are registered trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
TYPICAL APPLICATIO
5V Step-Down Converter
VIN
6.5V TO 25V
VIN BD
OFF ON
RUN/SS
BOOST
10μF
680pF
15k
63.4k
VC LT1913
RT
PG
SYNC
GND
SW
FB
VOUT
5V
3.5A
0.47μF
4.7μH
536k
100k
47μF
1913 TA01a
Efficiency
100
VIN = 12V
90
80 VIN = 24V
70
60 VOUT = 5V
L = 4.7μH
f = 600kHz
50
0 0.5 1 1.5 2 2.5
OUTPUT CURRENT (A)
3 3.5
1913 G01
1913f
1
1 page  
LT1913
TYPICAL PERFOR A CE CHARACTERISTICS TA = 25°C unless otherwise noted.
Feedback Voltage
840
820
800
780
760
–50 –25
0 25 50 75 100 125 150
TEMPERATURE (°C)
1913 G12
Minimum Switch On-Time
140
120
100
80
60
40
20
0
–50 –25
0 25 50 75 100 125 150
TEMPERATURE (°C)
1913 G15
Boost Diode
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0
0 0.5 1.0 1.5 2.0
BOOST DIODE CURRENT (A)
1913 G18
Switching Frequency
1.20
RT = 34.0k
1.15
1.10
1.05
1.00
0.95
0.90
0.85
0.80
–50 –25
0 25 50 75 100 125 150
TEMPERATURE (°C)
1913 G13
Soft-Start
7
6
5
4
3
2
1
0
0 0.5 1 1.5 2 2.5 3 3.5
RUN/SS PIN VOLTAGE (V)
1913 G16
Error Amp Output Current
50
40
30
20
10
0
–10
–20
–30
–40
–50
–200
–100
0
100
FB PIN ERROR VOLTAGE (mV)
200
1913 G19
Frequency Foldback
1200
RT = 34.0k
1000
800
600
400
200
0
0 100 200 300 400 500 600 700 800 900
FB PIN VOLTAGE (mV)
1913 G14
RUN/SS Pin Current
12
10
8
6
4
2
0
0
5
10 15 20
25
RUN/SS PIN VOLTAGE (V)
1913 G17
Minimum Input Voltage
5.0
4.5
4.0
3.5
3.0
VOUT = 3.3V
2.5 TA = 25°C
L = 4.7μH
f = 600kHz
2.0
1 10 100 1000
LOAD CURRENT (mA)
10000
1913 G20
1913f
5
5 Page 
LT1913
APPLICATIONS INFORMATION
operating input voltage. Conversely, a lower switching
frequency will be necessary to achieve safe operation at
high input voltages.
If the output is in regulation and no short-circuit, start-
up, or overload events are expected, then input voltage
transients of up to 25V are acceptable regardless of the
switching frequency. In this mode, the LT1913 may enter
pulse skipping operation where some switching pulses
are skipped to maintain output regulation. In this mode
the output voltage ripple and inductor current ripple will
be higher than in normal operation.
The minimum input voltage is determined by either the
LT1913’s minimum operating voltage of ~3.6V or by its
maximum duty cycle (see equation in previous section).
The minimum input voltage due to duty cycle is:
VIN(MIN)
=
VOUT + VD
1– fSW tOFF(MIN)
–
VD
+
VSW
where VIN(MIN) is the minimum input voltage, and tOFF(MIN)
is the minimum switch off time (150ns). Note that higher
switching frequency will increase the minimum input
voltage. If a lower dropout voltage is desired, a lower
switching frequency should be used.
Inductor Selection
For a given input and output voltage, the inductor value
and switching frequency will determine the ripple current.
The ripple current ΔIL increases with higher VIN or VOUT
and decreases with higher inductance and faster switch-
ing frequency. A reasonable starting point for selecting
the ripple current is:
ΔIL = 0.4(IOUT(MAX))
where IOUT(MAX) is the maximum output load current. To
guarantee sufficient output current, peak inductor current
must be lower than the LT1913’s switch current limit (ILIM).
The peak inductor current is:
IL(PEAK) = IOUT(MAX) + ΔIL/2
where IL(PEAK) is the peak inductor current, IOUT(MAX) is
the maximum output load current, and ΔIL is the inductor
ripple current. The LT1913’s switch current limit (ILIM) is
5.5A at low duty cycles and decreases linearly to 4.5A at
DC = 0.8. The maximum output current is a function of
the inductor ripple current:
IOUT(MAX) = ILIM – ΔIL/2
Be sure to pick an inductor ripple current that provides
sufficient maximum output current (IOUT(MAX)).
The largest inductor ripple current occurs at the highest
VIN. To guarantee that the ripple current stays below the
specified maximum, the inductor value should be chosen
according to the following equation:
L
=
VOUT + VD
fSW IL
1–
VOUT + VD
VIN(MAX)
where VD is the voltage drop of the catch diode (~0.4V),
VIN(MAX) is the maximum input voltage, VOUT is the output
voltage, fSW is the switching frequency (set by RT), and
L is in the inductor value.
The inductor’s RMS current rating must be greater than the
maximum load current and its saturation current should be
about 30% higher. To keep the efficiency high, the series
resistance (DCR) should be less than 0.05 , and the core
material should be intended for high frequency applications.
Table 1 lists several vendors and suitable types.
Table 1. Inductor Vendors
VENDOR URL
Murata www.murata.com
TDK www.componenttdk.com
Toko www.toko.com
Sumida www.sumida.com
NEC www.nec.com
PART SERIES
LQH55D
SLF10145
D75C
D75F
CDRH74
CR75
CDRH8D43
MPLC073
MPBI0755
TYPE
Open
Shielded
Shielded
Open
Shielded
Open
Shielded
Shielded
Shielded
Of course, such a simple design guide will not always re-
sult in the optimum inductor for your application. A larger
value inductor provides a slightly higher maximum load
current and will reduce the output voltage ripple. If your
1913f
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11 Page | ||
| Páginas | Total 24 Páginas | |
| PDF Descargar | [ Datasheet LT1913.PDF ] | |
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