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PDF LTC1502CMS8-3.3 Data sheet ( Hoja de datos )
| Número de pieza | LTC1502CMS8-3.3 | |
| Descripción | Single Cell to 3.3V Regulated Charge Pump DC/DC Converter | |
| Fabricantes | Linear Technology | |
| Logotipo |  |
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FEATURES
s Input Voltage Range: 0.9V to 1.8V
s 0.9V Guaranteed Start-Up Voltage
s Regulated Output Voltage: 3.3V ±4%
s Output Current: 10mA (VIN ≥ 1V)
s No Inductors
s Shutdown Disconnects Load from VIN
s Low Operating Current: 40µA
s Low Shutdown Current: 5µA
s Short-Circuit and Overtemperature Protected
s Application Circuit Fits in < 0.125in2 PCB Area
s Available in 8-Pin MSOP and SO Packages
U
APPLICATIO S
s Pagers
s Battery Backup Supplies
s Portable Electronic Equipment
s Handheld Medical Instruments
s Glucose Meters
LTC1502-3.3
Single Cell to 3.3V
Regulated Charge Pump
DC/DC Converter
DESCRIPTIO
The LTC®1502-3.3 is a quadrupler charge pump DC/DC
converter that produces a regulated 3.3V output from a
single alkaline cell input. It requires only five small external
capacitors—no inductors are required. Low supply cur-
rent (40µA typical, 5µA in shutdown) and minimal external
components make the LTC1502-3.3 ideal for space and
power conscious single-cell applications. The total printed
circuit board area of the circuit shown below is less than
0.125in2.
Forcing the C1–/SHDN pin low through an external resis-
tive pull-down puts the part into shutdown mode. During
shutdown, the internal oscillator is stopped and the load is
disconnected from VIN. An internal pull-up current on the
C1–/SHDN pin forces the part back into normal operation
once the pull-down resistance is removed.
The LTC1502-3.3 is short-circuit protected and survives
an indefinite VOUT short to ground. The LTC1502-3.3 is
available in 8-pin MSOP and SO packages.
, LTC and LT are registered trademarks of Linear Technology Corporation.
TYPICAL APPLICATIO
Single Cell to 3.3V DC/DC Converter
10µF
1
2
1µF 3
4
C2 VOUT
C1+ C3+
LTC1502-3.3
C1–/SHDN C3 –
GND VIN
8
7
6
5
1µF
10µF
VOUT = 3.3V
10µF IOUT = 10mA
VIN
SINGLE CELL
NiCd or
ALKALINE
1502-3.3 TA01
PCB LAYOUT FITS IN < 0.125IN2
Output Voltage vs Input Voltage
3.5
TA = 25°C
3.4
3.3
3.2
IOUT = 10mA
IOUT = 15mA
3.1
3.0
0.8
1.0 1.2 1.4 1.6
INPUT VOLTAGE (V)
1.8
1502-3.3 TA02
1
1 page  
TEST CIRCUIT
SWITCH
CLOSED FOR
SHUTDOWN
LTC1502-3.3
10µF
100Ω
1
2
1µF 3
4
C2 VOUT
C1+ C3+
LTC1502-3.3
C1–/SHDN C3 –
GND VIN
8
7
6
5
100pF
10µF
IOUT
1µF
10µF
VIN
1502-3.3 TC
APPLICATIONS INFORMATION
Regulator Operation
The LTC1502-3.3 uses a quadrupler charge pump DC/DC
converter to produce a boosted output voltage. The
quadrupler charge pump consists of two voltage doubler
charge pumps (CP1 and CP2 on the Block Diagram)
cascaded in series. CP1 doubles the input voltage VIN and
the CP1 output voltage is stored on external capacitor C2.
The C2 pin also serves as the input for doubler CP2 whose
output is stored on the output capacitor COUT. Each
doubler is controlled by a two-phase clock which is
generated in the Timing Control circuit. On phase one of
the clock, the flying capacitors C1 and C3 are charged to
their respective input voltages. On phase two each charged
flying capacitor is stacked on top of the input voltage and
discharged through an internal switch onto its respective
output. This sequence of charging and discharging the
CP1 and CP2 flying capacitors continues at the free
running oscillator frequency (500kHz typ) until the output
is in regulation.
Regulation is achieved by comparing the divided down
output voltage to a fixed voltage reference. The charge
pump clocks are disabled when the output voltage is
above the desired regulation point set by COMP1. When
the output has dropped below the lower trip point of
COMP1, the charge pump clocks are turned back on until
VOUT is boosted back into regulation.
Enhanced Start-Up
Enhanced start-up capability is provided by the COMP2
circuitry. COMP2 compares the divided down C2 voltage
to the input voltage VIN. The COMP2 output disables the
output charge pump CP2 whenever the divided C2 voltage
is lower than VIN. The CP2 output is thereby forced into a
high impedance state until the voltage on C2 has been
raised above VIN (the C2 pin should not be loaded for
proper start-up). This allows a higher internal gate drive
voltage to be generated (from the C2 pin) before the output
(VOUT) is connected to a load. Hysteresis in COMP2 forces
CP2 to be turned ON and OFF while COUT is charging up to
prevent a lockup condition if C2 droops too low during
start-up. By the time the output nears the regulation point,
the C2 voltage is well above the lower trip point of COMP2
and CP2 will remain enabled. This method of disabling the
output charge pump while an internal boosted gate drive
supply is developed allows the part to start up at low
voltages with a larger output current load than would
otherwise be possible.
Shutdown
Shutdown is implemented using an external pull-down
device on the C1–/SHDN pin. The recommended external
pull-down device is an open-drain FET with resistive cur-
rent limiting (see Figure 1). The pull-down device must sink
up to 300µA and pull down below 0.2V to ensure proper
shutdown operation, however, the actual series resistance
is not critical. The pull-down device must also go into a Hi-
Z state for the LTC1502-3.3 to become active.
The timing control circuitry forces the CP1 switches into
a high impedance state every 16 clock cycles. The Hi-Z
duration is equal to one clock cycle. At the end of the
Hi-Z time interval, the voltage on the C1–/SHDN pin is
sampled. If the C1–/SHDN pin has been pulled to a logic
low state, the part will go into shutdown mode. When the
pull-down device is disabled, an internal pull-up current
5
5 Page | ||
| Páginas | Total 8 Páginas | |
| PDF Descargar | [ Datasheet LTC1502CMS8-3.3.PDF ] | |
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