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PDF LTC1514CS8-3.3 Data sheet ( Hoja de datos )
| Número de pieza | LTC1514CS8-3.3 | |
| Descripción | Step-Up/Step-Down Switched Capacitor DC/DC Converters with Low-Battery Comparator | |
| Fabricantes | Linear Technology | |
| Logotipo |  |
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Hay una vista previa y un enlace de descarga de LTC1514CS8-3.3 (archivo pdf) en la parte inferior de esta página. Total 8 Páginas | ||
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FEATURES
s 3.3V or 5V Output Voltages
s 2V to 10V Input Voltage Range
s Up to 50mA Output Current
s Only Three External Capacitors Required
s Soft Start Limits Inrush Current at Turn-On
s Low Operating Current: 60µA
s Low Shutdown Current: 10µA
s Shutdown Disconnects Load from VIN
s Short-Circuit and Overtemperature Protected
s 650kHz Switching Frequency
s Low-Battery Comparator Active in Shutdown
s Available in SO-8 Package
U
APPLICATIONS
s Battery-Operated Equipment
s Smart Card Readers
s Local Power Supplies
s Handheld Instruments
s Battery Backup Supplies
LTC1514-3.3/LTC1514-5
Step-Up/Step-Down Switched
Capacitor DC/DC Converters
with Low-Battery Comparator
DESCRIPTION
The LTC®1514-3.3/LTC1514-5 are micropower switched
capacitor DC/DC converters that produce a regulated
output voltage by either stepping up or stepping down
the input voltage. Output voltage is fixed at either 3.3V
(LTC1514-3.3) or 5V (LTC1514-5) by an internal resistor
divider.
A unique architecture allows the parts to accommodate
a wide input voltage range (2V to 10V) while maintaining
±4% regulation. Additional circuitry prevents excessive
inrush current and output voltage ripple when large VIN
to VOUT differentials are present.
An internal uncommitted comparator is kept active in
shutdown. The comparator has an open-drain output for
flexible interfacing.
The parts are short-circuit and overtemperature pro-
tected. Battery life is maximized by very low operating
currents (ICC = 60µA typ, 10µA in shutdown). Both parts
are available in an SO-8 package.
, LTC and LT are registered trademarks of Linear Technology Corporation.
TYPICAL APPLICATION
5V Step-Up/Step-Down Power Supply with Low-Battery Detect
ON OFF
LOW BAT
1.33M
1%
499k
1%
100k
LTC1514-5
1
SHDN
2
LBO
3
LBI
4
GND
VOUT
VIN
C1+
C1–
8
7
6
5
+
0.22µF
VOUT = 5V
IOUT = 50mA
10µF
+
10µF
VIN
4-CELL
NiCd
1514 TA01
LTC1514-5 Output Voltage
vs Input Voltage
5.2
IOUT = 10mA
5.1
5.0
4.9
4.8
2 3 4 5 6 7 8 9 10
INPUT VOLTAGE (V)
LT1514 • TA02
1
1 page  
LTC1514-3.3/LTC1514-5
PIN FUNCTIONS
battery comparator and 1.145V reference are kept alive in
shutdown.
GND (Pin 4): Ground. Should be tied to a ground plane for
best performance.
C1– (Pin 5): Charge Pump Flying Capacitor, Negative
Terminal.
C1+ (Pin 6): Charge Pump Flying Capacitor, Positive
Terminal.
VIN (Pin 7): Charge Pump Input Voltage. May be between
2V and 8V (LTC1514-3.3) or between 2.7V and 10V
(LTC1514-5). VIN should be bypassed with a ≥ 10µF low
ESR capacitor as close as possible to the pin for best
performance.
VOUT (Pin 8): Regulated Output Voltage. The output volt-
age is internally set to either 3.3V (LTC1514-3.3) or to 5V
(LTC1514-5) using an internal resistor divider. VOUT should
be bypassed with a ≥ 10µF low ESR capacitor as close as
possible to the pin for best performance.
APPLICATIONS INFORMATION
Regulator Operation
The regulator section of the LTC1514-3.3/LTC1514-5
consists of a charge pump, reference, comparator and
some logic. The divided down output voltage is com-
pared to the internal reference voltage. When the divided
output drops below the reference voltage, the charge
pump is enabled, which boosts the output back into
regulation. Hysteresis in the comparator forces the regu-
lator to burst on and off and causes approximately
100mV of peak-to-peak ripple to appear at the output. By
enabling the charge pump only when needed, the
LTC1514-3.3 and LTC1514-5 are able to achieve high
efficiencies with low output load currents.
Each part’s charge pump has a unique architecture that
allows the input voltage to be either stepped up or
stepped down to produce a regulated output. Internal
circuitry senses the VIN to VOUT differential voltage and
controls the charge pump operating mode. In addition,
the effective output impedance of the charge pump is
internally adjusted to prevent large inrush currents and
allow for a wide input voltage range. When the input
voltage is lower than the output voltage, the charge pump
operates as a step-up voltage doubler. When the input
voltage is greater than the output, the charge pump
operates as a step-down gated switch.
Capacitor Selection
For best performance, low ESR capacitors are recom-
mended for both CIN and COUT to reduce noise and ripple.
The CIN and COUT capacitors should be either ceramic or
tantalum and should be 10µF or greater. If the input
source impedance is very low (< 0.5Ω), CIN may not be
needed. Increasing the size of COUT to 22µF or greater will
reduce output voltage ripple—particularly with high VIN
voltages (8V or greater). A ceramic capacitor is recom-
mended for the flying capacitor C1 with a value of 0.1µF
or 0.22µF. Smaller value flying capacitors may be used in
low output current applications.
Output Ripple
Normal LTC1514-3.3/LTC1514-5 operation produces
voltage ripple on the VOUT pin. Output voltage ripple is
required for the parts to regulate. Low frequency ripple
exists due to the hysteresis 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 (VIN < 8V) under maxi-
mum load is 100mV peak-to-peak with a low ESR (< 0.5Ω)
10µF output capacitor. For applications requiring VIN to
exceed 8V, a 22µF or larger COUT capacitor is recom-
mended to maintain max ripple in the 100mV range.
The magnitude of the ripple voltage depends on several
factors. High input voltages increase the output ripple
since more charge is delivered to COUT per charging
cycle. A large C1 flying capacitor (> 0.22µF) also
increases ripple in step-up mode for the same reason.
Large output current load and/or a small output capacitor
(< 10µF) results in higher ripple due to higher output
voltage dV/dt. High ESR capacitors (ESR > 0.5Ω) on the
5
5 Page | ||
| Páginas | Total 8 Páginas | |
| PDF Descargar | [ Datasheet LTC1514CS8-3.3.PDF ] | |
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