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PDF LTC1517-5 Data sheet ( Hoja de datos )
| Número de pieza | LTC1517-5 | |
| Descripción | Micropower/ Regulated 5V Charge Pump in a 5-Pin SOT-23 Package | |
| Fabricantes | Linear Technology | |
| Logotipo |  |
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FEATURES
s Ultralow Power: ICC = 6µA Typ
s Short-Circuit/Thermal Protected
s 5V ±4% Regulated Output
s VIN Range: 2.7V to 5V
s Output Current: 10mA (VIN ≥ 2.7V)
20mA (VIN ≥ 3V)
s No Inductors
s Ultrasmall Application Circuit (0.045in2)
s 800kHz Switching Frequency
s Available in 5-Pin SOT-23
U
APPLICATIONS
s Cellular Telephones
s Battery-Operated Equipment
s Local Power Supplies
s Handheld Instruments
s PCMCIA Supplies
LTC1517-5
Micropower, Regulated
5V Charge Pump in a
5-Pin SOT-23 Package
DESCRIPTION
The LTC®1517-5 is a micropower charge pump DC/DC
converter that produces a regulated 5V output. The input
voltage range is 2.7V to 5V. Extremely low operating current
(typically 6µA with no load) and low external parts count (one
0.1µF flying capacitor and two small bypass capacitors at VIN
and VOUT) make the part ideally suited for small, light load
battery-powered applications. The total printed circuit board
area of the application circuit shown below is only 0.045in2.
The part operates as a Burst ModeTM switched-capacitor
voltage doubler to produce a regulated output. The part has
thermal shutdown capability and can survive a continuous
short circuit from VOUT to GND. The device is available in a
5-pin SOT-23 package.
, LTC and LT are registered trademarks of Linear Technology Corporation.
Burst Mode is a trademark of Linear Technology Corporation.
TYPICAL APPLICATION
0.1µF
54
C1– C1+
LTC1517-5
VIN
2.7V TO 5V
VIN
1
3.3µF
GND VOUT
23
VOUT = 5V ± 4%
IOUT = 10mA (VIN ≥ 2.7V)
6.8µF IOUT = 20mA (VIN ≥ 3V)
1517 TA01
Typical Output Voltage vs Output Current
5.2
TA = 25°C
C1 = 0.1µF
COUT = 6.8µF
5.1
5.0
4.9
4.8
0
VIN = 2.7V VIN = 3V VIN = 3.3V
20 40 60
OUTPUT CURRENT (mA)
80
1517 TA02
1
1 page  
LTC1517-5
APPLICATIONS INFORMATION
Operation
The LTC1517-5 uses a switched-capacitor charge pump
to boost VIN to a 5V ±4% regulated output. The part
achieves regulation by sensing the output voltage through
an internal resistor divider and enabling the charge pump
when the divided output droops below the comparator’s
lower trip point (set by VREF). When the charge pump is
enabled, a 2-phase nonoverlapping clock controls the
internal charge pump switches. Flying capacitor C1 is
charged to VIN on phase one of the clock. On phase two of
the clock, C1 is stacked in series with VIN and connected
to VOUT through an internal switch. This sequence of
charging and discharging the flying capacitor occurs at a
free running frequency of 800kHz (typ) and continues until
the divided output voltage reaches the upper trip point of
the comparator. Once the output is back in regulation, the
charge pump is disabled. This method of bursting the
charge pump on and off enables the LTC1517-5 to achieve
high efficiency at extremely low output loads.
Capacitor Selection
For best performance, it is recommended that low ESR
capacitors be used for both CIN and COUT to reduce noise
and ripple. The CIN and COUT capacitors should be either
ceramic or tantalum and should be 3.3µF or greater.
Ceramic capacitors will provide the smallest size and
lowest ESR for a given capacitance. If the input source
impedance is very low (< 0.5Ω), CIN may not be needed.
Ceramic capacitors are recommended for the flying ca-
pacitor C1 with values of 0.1µF or 0.22µF. Smaller value
flying capacitors may be used in low IOUT applications.
Output Ripple
Normal LTC1517-5 operation produces voltage ripple on
the VOUT pin. Output voltage ripple is required for the part
to regulate. Low frequency ripple exists due to the hyster-
esis in the sense comparator and propagation delays in the
charge pump enable/disable circuits. High frequency ripple
is also present mainly from the ESR (equivalent series
resistance) in the output capacitor. Typical output ripple
with VIN = 3V under maximum load is 100mV peak-to-peak
with a low ESR (< 0.5Ω) 3.3µF output capacitor (minimum
recommended COUT). For applications requiring VIN to
exceed 3.3V or for applications requiring < 100mV of
peak-to-peak ripple, a 6.8µF to 10µF COUT capacitor is
recommended. Slight further decreases in output ripple
can be achieved by using COUT capacitors larger than
10µF.
Short-Circuit/Thermal Protection
During short-circuit conditions, the LTC1517-5 will draw
between 50mA and 200mA from VIN, causing a rise in
junction temperature. On-chip thermal shutdown circuitry
disables the charge pump once the junction temperature
exceeds approximately 160°C. The charge pump is
reenabled once the junction temperature drops to approxi-
mately 145°C. The LTC1517-5 will cycle in and out of
thermal shutdown indefinitely without latchup or damage
until the VOUT short is removed.
5
5 Page | ||
| Páginas | Total 8 Páginas | |
| PDF Descargar | [ Datasheet LTC1517-5.PDF ] | |
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