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PDF LTC3245 Data sheet ( Hoja de datos )
| Número de pieza | LTC3245 | |
| Descripción | 250mA Buck-Boost Charge Pump | |
| Fabricantes | Linear Technology | |
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LTC3245
Features
Wide VIN Range,
Low Noise, 250mA Buck-Boost
Charge Pump
Description
n 2.7V to 38V VIN Range
n IQ = 18µA Operating; 4μA in Shutdown
n 12V to 5V Efficiency = 81%
n Multimode Operation (2:1, 1:1, 1:2) with Automatic
Mode Switching
n Low Noise, Constant Frequency Operation
n Pin Selectable Burst Mode® Operation
n VOUT: Fixed 3.3V, 5V or Adjustable (2.5V to 5V)
n IOUT Up to 250mA
n Overtemperature and Short-Circuit Protection
n Operating Junction Temperature: 150°C Maximum
n Thermally Enhanced 12-Pin MSOP and Low Profile
12-Pin (3mm × 4mm) DFN Packages
Applications
n Automotive ECU/CAN Transceiver Supplies
n Industrial Housekeeping Supplies
n Low Power 12V to 5V Conversion
L, LT, LTC, LTM, Burst Mode, Linear Technology and the Linear logo are registered trademarks
and ThinSOT is a trademark of Linear Technology Corporation. All other trademarks are the
property of their respective owners.
The LTC®3245 is a switched capacitor buck-boost DC/DC
converter that produces a regulated output (3.3V, 5V or
adjustable) from a 2.7V to 38V input. The device uses
switched capacitor fractional conversion to maintain
regulation over a wide range of input voltage. Internal
circuitry automatically selects the conversion ratio to
optimize efficiency as input voltage and load conditions
vary. No inductors are required.
The unique constant frequency architecture provides a
lower noise output than conventional charge pump regu-
lators. To optimize efficiency at the expense of slightly
higher output ripple, the device has pin selectable Burst
Mode operation.
Low operating current (20μA with no load, 4μA in shut-
down) and low external parts count (three small ceramic
capacitors) make the LTC3245 ideally suited for low power,
space constrained automotive/industrial applications. The
device is short-circuit and overtemperature protected, and
is available in thermally enhanced 12-pin MSOP and low
profile 3mm × 4mm 12-pin DFN packages.
Typical Application
Efficient Regulated 5V Output
1µF
C+ C–
LTC3245
VIN = 2.7V TO 38V
VIN VOUT
SEL2 OUTS/ADJ
1µF
BURST
PGOOD
SEL1
GND
3245 TA01a
500k
VOUT = 5V
IOUT UP TO 250mA
10µF
5VOUT Efficiency vs Output Current
90
VIN = 12V
80
70
EFFICIENCY
400
350
300
60 250
50 200
40 150
PLOSS
30 100
20 50
10
0.1
0
1 10 100 1000
IOUT (mA)
3245 TA01b
For more information www.linear.com/LTC3245
3245f
1
1 page  
LTC3245
Typical Performance Characteristics TA = 25°C, unless otherwise noted.
5V Fixed Output Voltage
vs Falling Input Voltage
(Burst Mode Operation)
5.100
3.3V Fixed Output Voltage
vs Falling Input Voltage
(Burst Mode Operation)
3.400
ADJ Regulation Voltage
vs Temperature
1.220
5.075
5.050
5.025
IOUT = 1mA
3.375
3.350
3.325
IOUT = 1mA
1.215
1.210
1.205
5.000
3.300
1.200
4.975
4.950
IOUT = 250mA
4.925
–55°C
25°C
4.900
125°C
2 3 4 5 6 7 8 9 10 11 12 13 14 15
VIN (V)
3245 G10
3.275
3.250
IOUT = 250mA
3.225
–55°C
25°C
125°C
3.200
2 3 4 5 6 7 8 9 10 11 12 13 14 15
VIN (V)
3245 G11
1.195
1.190
1.185
1.180
–60 –30
0 30 60 90
TEMPERATURE (°C)
120 150
3245 G12
5V Output Impedance
vs Temperature (Boost Mode)
30
VIN = 2.7V
25
VIN = 3.3V
20
LOW NOISE
15
10
Burst Mode OPERATION
5
0
–60 –30
0 30 60 90
TEMPERATURE (°C)
120 150
3245 G13
3.3V Output Impedance
vs Temperature (Boost Mode)
40
35 VIN = 3.3V VIN = 2.7V
30
LOW NOISE
25
20
15
10 Burst Mode OPERATION
5
0
–60 –30
0 30 60 90
TEMPERATURE (°C)
120 150
3245 G14
Output Current vs Input Voltage
(VOUT 5% Below Regulation)
800
5V Burst Mode
700 OPERATION
5V LOW NOISE
600
500
400
3.3V LOW NOISE
300
3.3V Burst Mode
200 OPERATION
100
0
2 3 4 5 6 7 8 9 10 11 12 13 14
VIN (V)
3245 G15
Operating Mode Transition
Voltage vs Input Voltage
12
11
IOUT = 1mA
10
9
8
7
6
RISING
FALLING
5 RISING
4
3 FALLING
2
BUCK
LDO
BOOST
1
0
2.5 3 3.5 4 4.5 5
VOUT (V)
3245 G16
Operating Mode Transition
Voltage vs Input Voltage
12
11
IOUT = 150mA
10
9
8 RISING
7 FALLING
6
5 RISING
4
3 FALLING
2
BUCK
LDO
BOOST
1
0
2.5 3 3.5 4 4.5 5
VOUT (V)
3245 G17
Operating Mode Transition
Voltage vs Input Voltage
12
11
IOUT = 250mA
10 RISING
9
8
7 FALLING
6
5
RISING
4
3
FALLING
2
BUCK
LDO
BOOST
1
0
2.5 3 3.5 4 4.5 5
VOUT (V)
3245 G18
For more information www.linear.com/LTC3245
3245f
5
5 Page 
LTC3245
Applications Information
strength. The value of COUT directly controls the amount
of output ripple for a given load current when operating
in constant frequency mode. 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. 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.
Both the style and value of COUT can significantly affect the
stability of the LTC3245. As shown in the Block Diagram,
the device uses a control loop to adjust the strength of the
charge pump to match the current required at the output.
The error signal of this loop is stored directly on the output
charge storage capacitor. The charge storage capacitor also
serves to form the dominant pole for the control loop. To
prevent ringing or instability it is important for the output
capacitor to maintain at least 4μF of capacitance over all
conditions (see Ceramic Capacitor Selection Guidelines).
Likewise excessive ESR on the output capacitor will tend
to degrade the loop stability of the LTC3245. The closed
loop output resistance of the device is designed to be 0.3Ω
for a 5V output and 0.2Ω for a 3.3V output. For a 250mA
load current change, the output voltage will change by
about 1.5%V. If the output capacitor has more ESR than
the closed loop impedance, the closed loop frequency
response will cease to roll off in a simple 1-pole fashion
and poor load transient response or instability could result.
Ceramic capacitors typically have exceptional ESR perfor-
mance, and combined with a tight board layout, should
yield excellent stability and load transient performance.
VIN Capacitor Selection
The constant frequency architecture used by the LTC3245
makes input noise filtering much less demanding than with
conventional regulated charge pumps. Depending on the
mode of operation the input current of the LTC3245 can
vary from IOUT to 0mA on a cycle-by-cycle basis. Low ESR
will reduce the voltage steps caused by changing input
current, while the absolute capacitor value will determine
the level of ripple. The total amount and type of capacitance
necessary for input bypassing is very dependant on the
applied source impedance as well as existing bypassing
already 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. An electrolytic or
tantalum capacitor may be used in parallel with the ce-
ramic 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 LTC3245 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
Warning: A polarized capacitor such as tantalum or alumi-
num should never be used for the flying capacitors since
the voltage can reverse upon start-up of the LTC3245.
Ceramic capacitors should always be used for the flying
capacitors. The flying capacitors control the strength of
the charge pump. In order to achieve the rated output
current, it is necessary for the flying capacitor 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). If only 100mA
or less of output current is required for the application,
the flying capacitor minimum can be reduced to 0.15μF.
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
For more information www.linear.com/LTC3245
3245f
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11 Page | ||
| Páginas | Total 16 Páginas | |
| PDF Descargar | [ Datasheet LTC3245.PDF ] | |
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