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PDF LTC1429 Data sheet ( Hoja de datos )
| Número de pieza | LTC1429 | |
| Descripción | Clock-Synchronized Switched Capacitor Regulated Voltage Inverter | |
| Fabricantes | Linear Technology | |
| Logotipo |  |
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FEATURES
s Regulated Negative Voltage from a Single
Positive Supply
s External Clock for Synchronization in Noise
Sensitive Systems
s REG Output Indicates Output is in Regulation
s Low Output Ripple: 5mV Typ
s Can Provide Regulated – 5V from a 3V Supply
s Supply Current: 600µA Typ
s Shutdown Mode Drops Supply Current to 0.2µA
s Up to 12mA Output Current
s Adjustable or Fixed Output Voltages
s Requires Only Three or Four External Caps
s Output Regulation: 5%
s Available in SO-8 Packages
U
APPLICATIONS
s GaAs FET Bias Generators
s Negative Supply Generators
s Battery Powered Systems
s 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
VOUT = –4V AT 10mA
C4
3.3µF
LTC1429 • TA01
Waveforms for –4V Generator with Power Valid
0V
VOUT
– 4V
5V
POWER VALID
0V
5V
SYNC/SD
0V
0.2ms/DIV
LTC1429 • TA02
1
1 page  
LTC1429
PIN FUNCTIONS
effect on output ripple; see the Applications Information
section for more details.
REG (Pin 12/Pin 7): This is an open drain output that pulls
low when the output voltage is within 5% of the set value.
It will sink 10mA to ground with a 5V supply. The external
circuitry must provide a pull-up or REG will not swing high.
The voltage at REG may exceed VCC; it can be pulled up to
12V above ground without damage.
SYNC/SD (Pin 13/Pin 8): Synchronous Clock Input. A
minimum input clock frequency (60kHz with VCC ≤ 5V and
100kHz with VCC = 6.5V) must be applied to this input to
keep the LTC1429 operating normally. An input clock
below the minimum frequency may cause the charge
pump to operate erratically or the device to shut down. A
logic high or low at the SYNC/SD pin will put the device
into SHUTDOWN and drop the supply current to 0.2µA.
The LTC1429 will operate with input square wave of 40%
to 60% duty cycle. For best performance, use a square
wave of 50% duty cycle.
VCC (Pin 14/Pin 1): Power Supply. This requires an input
voltage between 3V and 6.5V. Certain combinations of
output voltage and operating mode may place additional
restrictions on the input voltage; see the Applications
Information section for details. VCC must be bypassed to
ground with at least a 0.1µF capacitor, placed in close
proximity to the chip; again, see the Applications Informa-
tion section.
TEST CIRCUITS
5V
10µF
0.1µF
1 VCC
SYNC/SD 8
2 C1+
7
REG
LTC1429-4CS8
3 C1–
6
OUT
4 GND
COMP 5
FSYNC = 700kHz
+
0.001µF
VOUT = –4V ± 5%
3.3µF
LTC1429 • TC01
Figure 1. Doubler Mode
0.1µF
0.1µF
VIN = 3.3V
10µF
+
2 C1+
3 C1–
14
10
VCC ADJ
0.001µF
RADJ 9
R1 8 NC
LTC1429CS
SYNC/SD 13
FSYNC = 700kHz
4 C2+
R0 7 NC
5 C2–
GND OUT 11
VOUT = –4V ± 5%
6 + 3.3µF
Figure 2. Tripler Mode
LTC1429 • TC02
APPLICATIONS INFORMATION
MODES OF OPERATION
The LTC1429 uses a charge pump to generate a negative
output voltage that can be regulated to a value either
higher or lower than the original input voltage. It has two
modes of operation: a doubler inverting mode, which can
provide a negative output equal to or less than the positive
power supply, and a tripler inverting mode, which can
provide negative output voltages either larger or smaller in
magnitude than the original positive supply. The tripler
offers greater versatility and wider input range but re-
quires four external capacitors and a 14-pin package; the
doubler offers the SO-8 package and requires only three
external capacitors. The optional compensation capacitor
at ADJ/COMP is used to reduce the ripple output voltage.
Doubler Mode
This mode allows the LTC1429 to generate negative
output voltage magnitudes up to that of the supply voltage,
5
5 Page 
LTC1429
APPLICATIONS INFORMATION
The internal resistor values are the same for the fixed
output versions of the LTC1429 as they are for the adjust-
able parts. The output voltage can be trimmed, if desired,
by connecting external resistance from the COMP pin to
OUT or ground to alter the divider ratio. As in the adjustable
parts, the absolute value of the internal resistors may vary
significantly from unit to unit. As a result, the further the
trim shifts the output voltage, the less accurate the output
voltage will be. If a precise output voltage other than one
of the available fixed voltages is required, it’s better to use
an adjustable LTC1429 and use precision external resis-
tors. The internal reference is trimmed at the factory to
within 3.5% of 1.24V. With 1% external resistors, the
output will be within 5.5% of the nominal value, even
under worst case conditions.
The LTC1429 can be internally configured with nonstand-
ard fixed output voltages. For details, contact the Linear
Technology Marketing Department.
TYPICAL APPLICATIONS
3.3V In, – 4.5V Out GaAs FET Bias Generator
5V In, – 4V Out GaAs FET Bias Generator
VBAT
3.3V
0.22µF
SYNC/SD
0.1µF
0.1µF
14
2
C1+
VCC
SYNC/SD
13
3 C1–
12
REG
LTC1429CS
4 C2+
11
OUT
5 C2–
ADJ 10
P-CHANNEL
POWER SWITCH
10k
–4.5V BIAS
+ 3.3µF
GaAs
TRANSMITTER
VBAT
SYNC/SD
18
5V VCC SYNC/SD
0.1µF
0.1µF
2 C1+
REG 7
LTC1429CS8-4
3 C2–
OUT 6
4 GND COMP 5
0.001µF
NC 8 R1
R0
7
9
RADJ
GND
6
0.001µF
LTC1429 • TA03
P-CHANNEL
POWER SWITCH
10k
– 4V BIAS
+ 3.3µF
GaAs
TRANSMITTER
LTC11429 • TA04
–5V Supply Generator
Minimum Parts Count – 4V Generator
18
5V VCC SYNC/SD
0.1µF
0.1µF
2 C1+
REG 7
LTC1429CS8-4
3 C1–
6
OUT
VOUT = –4V
45
GND COMP
+ 3.3µF
LTC11429 • TA07
0.1µF
0.1µF
3V ≤ VCC ≤ 7V
0.22µF
14
VCC 10
ADJ
2 C1+
9
3 C1–
RADJ
13
SYNC/SD
0.001µF
LTC1429CS
8
R1 NC
4 C2+
R0 7 NC
5 C2–
11
OUT
VOUT = –5V ±5%
AT 10mA
GND + 3.3µF
6
LTC1429 • TA06
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no represen-
tation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
11
11 Page | ||
| Páginas | Total 12 Páginas | |
| PDF Descargar | [ Datasheet LTC1429.PDF ] | |
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