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PDF LTC1261CS8-4 Data sheet ( Hoja de datos )
| Número de pieza | LTC1261CS8-4 | |
| Descripción | Switched Capacitor Regulated Voltage Inverter | |
| Fabricantes | Linear Technology | |
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LTC1261
Switched Capacitor
Regulated Voltage Inverter
FEATURES
s Regulated Negative Voltage from a
Single Positive Supply
s Can Provide Regulated – 5V from a 3V Supply
s REG Pin Indicates Output is in Regulation
s Low Output Ripple: 5mV Typ
s Supply Current: 600µA Typ
s Shutdown Mode Drops Supply Current to 5µA
s Up to 15mA Output Current
s Adjustable or Fixed Output Voltages
s Requires Only Three or Four External Capacitors
s Available in SO-8 Packages
APPLICATI S
s GaAs FET Bias Generators
s Negative Supply Generators
s Battery-Powered Systems
s Single Supply Applications
DESCRIPTIO
The LTC®1261 is a switched-capacitor voltage inverter
designed to provide a regulated negative voltage from a
single positive supply. The LTC1261CS 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 LTC1261CS to be configured for output volt-
ages of – 3.5V, – 4V, – 4.5V or – 5V with no external
components. The LTC1261CS8 is optimized for applica-
tions which use a 5V or higher supply or which require
low output voltages. It requires a single external 0.1µF
capacitor and provides adjustable and fixed output voltage
options in 8-pin SO packages. The LTC1261CS requires
one or two external 0.1µF capacitors, depending on input
voltage. Both versions require additional external input
and output bypass capacitors. An optional compensation
capacitor at ADJ/COMP can be used to reduce the output
voltage ripple.
Each version of the LTC1261 will supply up to 12mA
output current with guaranteed output regulation of 5%.
The LTC1261 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. Quiescent current
is typically 600µA when operating and 5µA in shutdown.
The LTC1261 is available in a 14-pin narrow body SO
package and an 8-pin SO package.
, LTC and LT are registered trademarks of Linear Technology Corporation.
TYPICAL APPLICATION
– 4V Generator with Power Valid
5V
C1 C2
1µF 0.1µF
*OPTIONAL
1
VCC
SHDN 8
2 C1+
REG 7
LTC1261-4
3 C1–
OUT 6
4
GND
COMP 5
5V
10k
C3*
100pF
POWER VALID
VOUT = –4V
AT 10mA
C4
+ 3.3µF
LTC1261 • TA01
Waveforms for – 4V Generator with Power Valid
0V
OUT
– 4V
5V
SHDN
0V
5V
POWER VALID
0V
0.2mS/DIV
LTC1261 • TAO2
1
1 page  
LTC1261
PIN FUNCTIONS
Pin numbers are shown as (LTC1261CS/LTC1261CS8).
NC (Pin 1/NA): No Internal Connection.
C1+ (Pin 2/ Pin 2): C1 Positive Input. Connect a 0.1µF
capacitor between C1+ and C1–. With the LTC1261CS in
doubler mode, connect a 0.1µF capacitor from C1+ to
C2 –.
C1– (Pin 3/Pin 3): C1 Negative Input. Connect a 0.1µF
capacitor from C1+ to C1–. With the LTC1261CS in
doubler mode only, C1– should float.
C2 + (Pin 4/NA): C2 Positive Input. In tripler mode con-
nect a 0.1µF capacitor from C2 + to C2 –. This pin is used
with the LTC1261CS in tripler mode only; in doubler
mode this pin should float.
C2 – (Pin 5/NA): C2 Negative Input. In tripler mode
connect a 0.1µF capacitor from C2 + to C2 –. In doubler
mode connect a 0.1µF capacitor from C1+ to C2 –.
GND (Pin 6/Pin 4): Ground. Connect to a low impedance
ground. A ground plane will help to minimize regulation
errors.
R0 (Pin 7/NA): Internal Resistor String, 1st Tap. See
Table 2 in the Applications Information section for infor-
mation on internal resistor string pin connections vs
output voltage.
R1 (Pin 8/NA): Internal Resistor String, 2nd Tap.
RADJ (Pin 9/NA): Internal Resistor String Output. Con-
nect this pin to ADJ to use the internal resistor divider.
See Table 2 in the Applications Information section for
information on internal resistor string pin connections vs
output voltage.
ADJ (COMP for fixed versions) (Pin 10/Pin 5): Output
Adjust/Compensation Pin. For adjustable parts this pin is
used to set the output voltage. The output voltage should
be divided down with a resistor divider and fed back to
this pin to set the regulated output voltage. The resistor
divider can be external or the internal divider string can
be used if it can provide the required output voltage.
Typically the resistor string should draw ≥ 10µA from the
output to minimize errors due to the bias current at the
adjust pin. Fixed output parts have the internal resistor
string connected to this pin inside the package. The pin
can be used to trim the output voltage if desired. It can
also be used as an optional feedback compensation pin
to reduce output ripple on both adjustable and fixed
output voltage parts. See Applications Information sec-
tion for more information on compensation and output
ripple.
OUT (Pin 11/Pin 6): Negative Voltage Output. This pin
must be bypassed to ground with a 1µF or larger capaci-
tor; it must be at least 3.3µF to provide specified output
ripple. The size of the output capacitor has a strong effect
on output ripple. See the Applications Information sec-
tion 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 8mA 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 and can be
pulled up to 12V above ground without damage.
SHDN (Pin 13/Pin 8): Shutdown. When this pin is at
ground the LTC1261 operates normally. An internal 5µA
pull-down keeps SHDN low if it is left floating. When
SHDN is pulled high, the LTC1261 enters shutdown
mode. In shutdown the charge pump stops, the output
collapses to 0V and the quiescent current drops to 5µA
typically.
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. VCC must be bypassed
to ground with at least a 0.1µF capacitor placed in close
proximity to the chip. See the Applications Information
section for details.
5
5 Page 
LTC1261
APPLICATIONS INFORMATION
Table 2. Output Voltages Using the Internal Resistor Divider
PIN CONNECTIONS
OUTPUT VOLTAGE
ADJ to RADJ
ADJ to RADJ, R0 to GND
ADJ to RADJ, R1 to R0
ADJ to RADJ, R1 to GND
ADJ to R1
– 5V
– 4.5V
– 4V
– 3.5V
– 1.77V
ADJ to R0
– 1.38V
ADJ to GND
– 1.24V
There are some oddball output voltages available by
connecting ADJ to R0 or R1 and shorting out some of the
internal resistors. If one of these combinations gives you
the output voltage you want, by all means use it!
The internal resistor values are the same for the fixed
output versions of the LTC1261 as they are for the adjust-
able. 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 is better to use
an adjustable LTC1261 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 LTC1261 can be internally configured with nonstand-
ard fixed output voltages. Contact the Linear Technology
Marketing Department for details.
TYPICAL APPLICATIONS N
3.3V Input, – 4.5V Output GaAs FET Bias Generator
VBAT
3.3V
1µF
P-CHANNEL
POWER SWITCH
SHUTDOWN
0.1µF
0.1µF
14
2
C1+
VCC
SHDN
13
3 C1–
12
REG
LTC1261
4 C2+
OUT 11
5 C2–
ADJ 10
NC 8 R1
R0
7
9
RADJ
GND
6
10k
–4.5V BIAS
+ 3.3µF
GaAs
TRANSMITTER
100pF
LTC1261 • TA03
11
11 Page | ||
| Páginas | Total 16 Páginas | |
| PDF Descargar | [ Datasheet LTC1261CS8-4.PDF ] | |
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