LTC1429_15 Datasheet, PDF (1/12 Pages) Linear Technology – Clock-Synchronized Switched Capacitor Regulated Voltage Inverter

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FOR INFORMATION PURPOSES ONLY
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FEATURES
I _{Regulated Negative Voltage from a Single}
Positive Supply
I _{External Clock for Synchronization in Noise}
Sensitive Systems
I _{REG Output Indicates Output is in Regulation}
I _{Low Output Ripple: 5mV Typ}
I _{Can Provide Regulated – 5V from a 3V Supply}
I _{Supply Current: 600µA Typ}
I _{Shutdown Mode Drops Supply Current to 0.2µA}
I _{Up to 12mA Output Current}
I _{Adjustable or Fixed Output Voltages}
I _{Requires Only Three or Four External Caps}
I _{Output Regulation: 5%}
I _{Available in SO-8 Packages}
U
APPLICATIONS
I _{GaAs FET Bias Generators}
I _{Negative Supply Generators}
I _{Battery Powered Systems}
I _{Single Supply Applications}
, LTC and LT are registered trademarks of Linear Technology Corporation.
LTC1429
Clock-Synchronized
Switched Capacitor
Regulated Voltage Inverter
DESCRIPTION
The LTC^®1429 is a switched-capacitor voltage inverter de-
signed to provide a regulated negative voltage from a single
positive supply and permits clock synchronization in noise
sensitive systems. The LTC1429CS operates from a single 3V
to 8V supply and provides an adjustable output voltage from
– 1.25V to –8V. An on-chip resistor string allows the
LTC1429CS to be configured for output voltages of –3.5V,
–4V, –4.5V or –5V. The LTC1429CS8 is optimized for
applications which require a fixed –4V output from a 5V
supply and requires only a single external 0.1µF flying
capacitor. The LTC1429CS requires one or two external
0.1µF capacitors, depending on input voltage. Both versions
require additional external input and output bypass capaci-
tors. An optional compensation capacitor at ADJ/COMP can
be used to reduce the output voltage ripple.
Each version of the LTC1429 guarantees output regulation of
5%. The LTC1429 includes an open-drain REG output which
pulls low when the output is within 5% of the set value. Output
ripple is typically as low as 5mV. The LTC1429 requires an
external clock applied to the SYNC/SD for normal operation
and consumes a typical quiescent current of 600µA. Holding
the SYNC/SD either high or low brings the device into
shutdown and the supply current drops to 0.2µA. For appli-
cations which don’t have a clock signal available, the LTC1261
provides the same functionality with an internal oscillator. For
applications which require output ripple below 1mV, see the
LTC1550/LTC1551. The LTC1429CS is available in a 14-pin
SO package and the LTC1429CS8 is available in an 8-pin SO
package.
TYPICAL APPLICATION
– 4V Generator with Power Valid
5V
C1
0.1µF
C2
0.1µF
1 _VCC
SYNC/SD ⁸
2 _C1+
7
REG
LTC1429-4CS8
3 _C1–
6
OUT
4 _GND
COMP ⁵
10k
*C3
0.001µF ₊
*OPTIONAL
5V
POWER VALID
V_OUT = –4V AT 10mA
C4
3.3µF
LTC1429 • TA01
Waveforms for –4V Generator with Power Valid
0V
V_OUT
– 4V
5V
POWER VALID
0V
SYNC/SD ^5V
0V
0.2ms/DIV
LTC1429 • TA02
1