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PDF LT3430 Data sheet ( Hoja de datos )
| Número de pieza | LT3430 | |
| Descripción | High Voltage 3A & 200kHz/100kHz Step-Down Switching Regulators | |
| Fabricantes | Linear Technology | |
| Logotipo |  |
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Hay una vista previa y un enlace de descarga de LT3430 (archivo pdf) en la parte inferior de esta página. Total 28 Páginas | ||
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FEATURES
■ Wide Input Range: 5.5V to 60V
■ 3A Peak Switch Current over All Duty Cycles
■ Constant Switching Frequency:
200kHz (LT3430)
100kHz (LT3430-1)
■ 0.1Ω Switch Resistance
■ Current Mode
■ Effective Supply Current: 2.5mA
■ Shutdown Current: 30µA
■ 1.2V Feedback Reference Voltage
■ Easily Synchronizable
■ Cycle-by-Cycle Current Limiting
■ Small, 16-Pin Thermally Enhanced TSSOP Package
APPLICATIONS
■ Industrial and Automotive Power Supplies
■ Portable Computers
■ Battery Chargers
■ Distributed Power Systems
LT343ww0w/.DLatTaS3he4et43U.c0om-1
High Voltage, 3A,
200kHz/100kHz Step-Down
Switching Regulators
DESCRIPTION
The LT®3430/LT3430-1 are monolithic buck switching
regulators that accept input voltages up to 60V. A high ef-
ficiency 3A, 0.1Ω switch is included on the die along with
all the necessary oscillator, control and logic circuitry. A
current mode architecture provides fast transient response
and excellent loop stability.
Special design techniques and a new high voltage process
achieve high efficiency over a wide input range. Efficiency
is maintained over a wide output current range by using
the output to bias the circuitry and by utilizing a supply
boost capacitor to saturate the power switch. Patented
circuitry* maintains peak switch current over the full duty
cycle range. A shutdown pin reduces supply current to
30µA and a SYNC pin can be externally synchronized with
a logic level input from 228kHz to 700kHz for the LT3430
or from 125kHz to 250kHz for the LT3430-1.
The LT3430/LT3430-1 are available in a thermally enhanced
16-pin TSSOP package.
, LT, LTC and LTM are registered trademarks of Linear Technology Corporation.
*US Patent # 6498466
TYPICAL APPLICATION
5V, 2A Buck Converter
MMSD914TI
VIN
5.5V*
TO 60V
4.7µF
100V
OFF ON
BOOST
VIN SW
LT3430**
SHDN
BIAS
SYNC
GND
FB
VC
0.68µF
22µH
30BQ060
+
15.4k
VOUT
5V
2A
100µF 10V
SOLID
TANTALUM
4.99k
3.3k
0.022µF
220pF
3430 TA01
*FOR INPUT VOLTAGES BELOW 7.5V, SOME RESTRICTIONS MAY APPLY
** SEE LT3430-1 CIRCUIT IN APPLICATIONS INFORMATION SECTION
Efficiency vs Load Current
100
VOUT = 5V
90
VIN = 12V
80 VIN = 42V
70
60
LT3430-1 L = 68µH
LT3430 L =27µH
50
0 0.5 1.0 1.5 2.0 2.5
LOAD CURRENT (A)
3430 TA02
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1
1 page  
TYPICAL PERFORMANCE CHARACTERISTICS
LT343ww0w/.DLatTaS3he4et43U.c0om-1
Switching Frequency
230
220
(LT3430)
210
200
190
180
170
–50
–25 0 25 50 75 100 125
JUNCTION TEMPERATURE (°C)
3430 G10
Minimum Input Voltage with
5V Output
7.5
TA = 25°C
7.0
6.5
MINIMUM INPUT
VOLTAGE TO START
6.0
5.5 MINIMUM INPUT
VOLTAGE TO RUN
5.0
0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0
LOAD CURRENT (A)
3430 G11
BOOST Pin Current
90
TA = 25°C
80
70
60
50
40
30
20
10
0
012
SWITCH CURRENT (A)
3
3430 G12
VC Pin Shutdown Threshold
2.1
1.9
1.7
1.5
1.3
1.1
0.9
0.7
–50 –25 0 25 50 75 100 125
JUNCTION TEMPERATURE (°C)
3430 G13
Switch Peak Current Limit
6.0
5.5
5.0
4.5
4.0
3.5
3.0
2.5
–50
–25 0 25 50 75 100 125
JUNCTION TEMPERATURE (°C)
3430 G16
Switch Voltage Drop
450
400
TJ = 125°C
350
300
TJ = 25°C
250
200
150
TJ = –40°C
100
50
0
0123
SWITCH CURRENT (A)
3430 G14
Switch Minimum ON Time
vs Temperature
600
500
400
300
200
100
0
–50 –25 0 25 50 75 100 125
JUNCTION TEMPERATURE (°C)
3430 G15
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5 Page 
LT343ww0w/.DLatTaS3he4et43U.c0om-1
APPLICATIONS INFORMATION
Peak switch and inductor current can be significantly higher
than output current, especially with smaller inductors
and lighter loads, so don’t omit this step. Powdered iron
cores are forgiving because they saturate softly, whereas
ferrite cores saturate abruptly. Other core materials fall
somewhere in between. The following formula assumes
continuous mode of operation, but errs only slightly on
the high side for discontinuous mode, so it can be used
for all conditions.
IPEAK
= IOUT
+
ILP-P
2
= IOUT
+
(VOUT )(VIN – VOUT )
(2)(VIN)(f)(L)
EMI
Decide if the design can tolerate an “open” core geometry
like a rod or barrel, which have high magnetic field radiation,
or whether it needs a closed core like a toroid to prevent
EMI problems. This is a tough decision because the rods
or barrels are temptingly cheap and small and there are
no helpful guidelines to calculate when the magnetic field
radiation will be a problem.
Additional Considerations
After making an initial choice, consider additional factors
such as core losses and second sourcing, etc. Use the
experts in Linear Technology’s Applications department
if you feel uncertain about the final choice. They have ex-
perience with a wide range of inductor types and can tell
you about the latest developments in low profile, surface
mounting, etc.
Maximum Output Load Current
Maximum load current for a buck converter is limited by
the maximum switch current rating (IP). The current rating
for the LT3430/LT3430-1 is 3A. Unlike most current mode
converters, the LT3430/LT3430-1 maximum switch current
limit does not fall off at high duty cycles. Most current
mode converters suffer a drop off of peak switch current
for duty cycles above 50%. This is due to the effects of
slope compensation required to prevent subharmonic
oscillations in current mode converters. (For detailed
analysis, see Application Note 19.)
The LT3430/LT3430-1 are able to maintain peak switch
current limit over the full duty cycle range by using patented
circuitry* to cancel the effects of slope compensation
on peak switch current without affecting the frequency
compensation it provides.
Maximum load current would be equal to maximum switch
current for an infinitely large inductor, but with finite
inductor size, maximum load current is reduced by one-
half peak-to-peak inductor current (ILP-P). The following
formula assumes continuous mode operation, implying
that the term on the right is less than one-half of IP.
IOUT(MAX) =
Continuous Mode
IP
–
ILP-P
2
=IP
−
(
VOUT
+ VF )(
2(L)
VIN
(f)
− VOUT
( VIN )
–
VF
)
For VOUT = 5V, VIN = 12V, VF(D1) = 0.52V, f = 200kHz and
L = 15µH:
( )( )IOUT(MAX)
=
3
−
(5 + 0.52)(12 − 5 – 0.52)
2 15 •10−6 200•103 (12)
= 3 − 0.5 = 2.5A
Note that there is less load current available at the higher
input voltage because inductor ripple current increases.
At VIN = 24V, duty cycle is 23% and for the same set of
conditions:
( )( )IOUT(MAX)
=
3
−
(5 + 0.52)(24 − 5 – 0.52)
2 15 •10−6 200•103 (24)
= 3 − 0.71= 2.29A
To calculate actual peak switch current with a given set
of conditions, use:
ISW(PEAK)
=
IOUT
+
ILP-P
2
=
IOUT
+
(VOUT
+
(VF ) VIN − VOUT
2(L)(f)(VIN)
–
VF )
*US Patent # 6,498,466
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11
11 Page | ||
| Páginas | Total 28 Páginas | |
| PDF Descargar | [ Datasheet LT3430.PDF ] | |
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