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PDF LTC3255 Data sheet ( Hoja de datos )
| Número de pieza | LTC3255 | |
| Descripción | Step-Down Charge Pump | |
| Fabricantes | Linear | |
| Logotipo |  |
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Hay una vista previa y un enlace de descarga de LTC3255 (archivo pdf) en la parte inferior de esta página. Total 16 Páginas | ||
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FEATURES
n Input Voltage Range: 4V to 48V
n Adjustable Regulated Output: 2.4V to 12.5V
n Output Current: 50mA Maximum
n 16μA Quiescent Current in Regulation at No Load
n Input Fault Protection from –52V to 60V
n Multimode Charge Pump (2:1, 1:1) with Automatic
Mode Switching Maintains Regulation Over Wide
VIN Range
n Input Voltage Shunt Mode for Current-Fed Applications
n Power Good Output
n Overtemperature and Short-Circuit Protection
n Operating Junction Temperature: 150°C Maximum
n Thermally Enhanced 10-Lead MSOP and 10-Lead
(3mm × 3mm) DFN packages
APPLICATIONS
n Industrial Control, Factory Automation, Sensors, and
SCADA Systems
n Housekeeping Power Supplies
n Current-Boosting Voltage Regulators for 4mA to
20mA Current Loops
LTC3255
Wide VIN Range
Fault Protected 50mA
Step-Down Charge Pump
DESCRIPTION
The LTC®3255 is a switched-capacitor step-down DC/DC
converter that produces a regulated output (2.4V to 12.5V
adjustable) from a 4V to 48V input. In applications where
the input voltage exceeds twice the output voltage, 2:1
capacitive charge pumping extends output current capabil-
ity beyond input supply current limits. At no load, Burst
Mode® operation cuts VIN quiescent current to 16µA.
With its integrated VIN shunt regulator, the LTC3255
excels in 4mA to 20mA current loop applications. The
device enables current multiplication; a 4mA input current
can power a 7.4mA load continuously. Alternatively, the
LTC3255 serves as a higher efficiency replacement for
linear regulators and provides a space-saving inductor-
free alternative to buck DC/DC converters.
The LTC3255 withstands reverse-polarity input supplies
and output short-circuits without damage. Safety features
including current limit and overtemperature protection
further enhance robustness. The LTC3255 is available in
thermally enhanced 10-lead MSOP and low profile 3mm
× 3mm 10-lead DFN packages.
L, LT, LTC, LTM, Linear Technology, the Linear logo and Burst Mode are registered trademarks
and ThinSOT is a trademark of Linear Technology Corporation. All other trademarks are the
property of their respective owners.
TYPICAL APPLICATION
7.4mA DC Supply from 4mA to 20mA Current Loop
1µF
+
4mA TO 20mA INPUT
>10V COMPLIANCE
–
VIN C+
C– VOUT
EN LTC3255
1µF SHUNT
PGOOD
BIAS GND
FB
0.1µF
220k
PGOOD
2.15M
OUTPUT
3.3V
7.4mA
10µF
1.21M
3255 TA01a
For more information www.linear.com/LTC3255
Available Output Current
vs Input Current
40
37
34
31
28
25
22
AVAILABLE
IOUT
INCREASED
IOUT CAPABILITY
19
16
13
10
INPUT
CURRENT
7
4
4 6 8 10 12 14 16 18 20
INPUT CURRENT (mA)
3255 TA01b
3255f
1
1 page  
LTC3255
TYPICAL PERFORMANCE CHARACTERISTICS TA = 25°C, unless otherwise noted.
3vs.3IVnOpUuTt
Efficiency
Voltage at
50mA
Load
100 SHUNT = GND
90
80
70
LTC3255
60
50
40
IDEAL LDO
30
20
10
4 6 8 10 12 14 16 18 20
INPUT VOLTAGE (V)
3255 G16
v5sVOInUpTuEtfVfiociletangcey at 50mA Load
100
SHUNT = GND
90
80
70
LTC3255
60
50
40
IDEAL LDO
30
20
10
5 7 9 11 13 15 17 19 21 23 25
INPUT VOLTAGE (V)
3255 G17
5vsVOOUuTtpEuffticCiuernrceynt
90 VIN = 12V
80
EFFICIENCY
120
100
70 80
60 60
50 40
40
30
0.1
POWER LOSS
1 10
OUTPUT CURRENT (mA)
20
0
100
3255 G18
Output Ripple
VOUT
20mV/DIV
AC-COUPLED
VIN = 12V
VOUT = 3.3V
IOUT = 5mA
40µs/DIV
Load Transient
VOUT
50mV/DIV
AC-COUPLED
3255 G10
50mA
IOUT 5mA
VIN = 12V
VOUT = 3.3V
40µs/DIV
3255 G11
2.5V Output Voltage
vs Falling Input Voltage
2.55
2.54
SHUNT = GND
IOUT = 50mA
2.53
2.52
2.51
2.50
2.49
2.48
2.47
2.46
2.45
23 4
56
78
VIN (V)
–60°C
25°C
125°C
9 10
3255 G12
3.3V Output Voltage
vs Falling Input Voltage
3.40
3.38
SHUNT = GND
IOUT = 50mA
3.36
3.34
3.32
3.30
3.28
3.26
3.24
3.22
3.20
23456789
VIN (V)
–60°C
25°C
125°C
10 11 12
3255 G13
5V Output Voltage
vs Falling Input Voltage
5.10
5.08
SHUNT = GND
IOUT = 50mA
5.06
5.04
5.02
5.00
4.98
4.96
4.94 –60°C
4.92 25°C
125°C
4.90
4 5 6 7 8 9 10 11 12 13 14 15
VIN (V)
3255 G14
12V Output Voltage
vs Falling Input Voltage
12.25
12.20
12.15
SHUNT = GND
IOUT = 50mA
12.10
12.05
12.00
11.95
11.90
11.85
–60°C
11.80
25°C
125°C
11.75
10 12 14 16 18 20 22 24 26 28 30
VIN (V)
3255 G15
For more information www.linear.com/LTC3255
3255f
5
5 Page 
LTC3255
APPLICATIONS INFORMATION
VOUT Ripple and Capacitor Selection
The type and value of capacitors used with the LTC3255
determine several important parameters such as output
ripple and charge pump strength. The value of COUT
directly controls the amount of output ripple for a given
load current. Increasing the size of COUT will reduce the
output ripple.
To reduce output noise and ripple, it is suggested that a
low ESR (equivalent series resistance < 0.1Ω) ceramic
capacitor (10μF or greater) be used for COUT. Ceramic
capacitors typically have exceptionally low ESR which,
combined with a tight board layout, should yield excellent
performance. Tantalum and aluminum capacitors can be
used in parallel with a ceramic capacitor to increase the
total capacitance but are not recommended to be used
alone because of their high ESR.
VIN Capacitor Selection
The total amount and type of capacitance necessary for
input bypassing is very dependent on the impedance of
the input power source as well as existing bypassing al-
ready on the VIN node. For optimal input noise and ripple
reduction, it is recommended that a low ESR ceramic
capacitor be used for CIN bypassing. Low ESR will reduce
the voltage steps caused by changing input current, while
the absolute capacitor value will determine the level of
ripple. An electrolytic or tantalum capacitor may be used
in parallel with the ceramic capacitor on CIN to increase
the total capacitance, but due to the higher ESR, it is not
recommended that an electrolytic or tantalum capacitor be
used alone for input bypassing. The LTC3255 will operate
with capacitors less than 1μF, but depending on the source
impedance, input noise can feed through to the output
causing degraded performance. For best performance,
1μF or greater total capacitance is suggested for CIN.
Flying Capacitor Selection
The flying capacitor should always be a ceramic type.
Polarized capacitors such as tantalum or aluminum electro-
lytics are not recommended. The flying capacitor controls
the strength of the charge pump. In order to achieve the
rated output current, it is necessary for the flying capaci-
tor to have at least 0.4μF of capacitance over operating
temperature with a bias voltage equal to the programmed
VOUT (see Ceramic Capacitor Selection Guidelines). The
voltage rating of the ceramic capacitor should be VOUT +
1V or greater.
Ceramic Capacitor Selection Guidelines
Capacitors of different materials lose their capacitance
with higher temperature and voltage at different rates.
For example, a ceramic capacitor made of X5R or X7R
material will retain most of its capacitance from –40°C
to 85°C, whereas a Z5U or Y5V style capacitor will lose
considerable capacitance over that range (60% to 80%
loss typical). Z5U and Y5V capacitors may also have a
very strong voltage coefficient, causing them to lose an
additional 60% or more of their capacitance when the rated
voltage is applied. Therefore, when comparing different
capacitors, it is often more appropriate to compare the
amount of achievable capacitance for a given case size
rather than discussing the specified capacitance value. For
example, over rated voltage and temperature conditions,
a 4.7μF, 10V, Y5V ceramic capacitor in an 0805 case may
not provide any more capacitance than a 1μF, 10V, X5R
or X7R available in the same 0805 case. In fact, over bias
and temperature range, the 1μF, 10V, X5R or X7R will
provide more capacitance than the 4.7μF, 10V, Y5V. The
capacitor manufacturer’s data sheet should be consulted
to determine what value of capacitor is needed to ensure
minimum capacitance values are met over operating
temperature and bias voltage. Table 1 is a list of ceramic
capacitor manufacturers in alphabetical order:
For more information www.linear.com/LTC3255
3255f
11
11 Page | ||
| Páginas | Total 16 Páginas | |
| PDF Descargar | [ Datasheet LTC3255.PDF ] | |
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