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PDF SPX2957 Data sheet ( Hoja de datos )
| Número de pieza | SPX2957 | |
| Descripción | 350mA Low Drop Out Voltage Regulator | |
| Fabricantes | Sipex | |
| Logotipo |  |
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Hay una vista previa y un enlace de descarga de SPX2957 (archivo pdf) en la parte inferior de esta página. Total 9 Páginas | ||
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FEATURES
• Output Accuracy 5V, 3.3V@ 350mA Output
• Very Low Quiescent Current
• Low Dropout Voltage
• Extremely Tight Load And Line Regulation
• Very Low Temperature Coefficient
• Current & Thermal Limiting
• Error Flag Warns Of Output Dropout
• Logic-Controlled Electronic Shutdown
• Output Programmable From 1.24V to 29V
SPX2955/56/57
350mA Low Drop Out Voltage Regulator
with Shutdown
(PRELIMINARY INFORMATION)
APPLICATIONS
• Battery Powered Systems
• Cordless Telephones
• Radio Control Systems
• Portable/Palm Top/Notebook Computers
• Portable Consumer Equipment
• Portable Instrumentation
• Automotive Electronics
• SMPS Post-Regulator
• Voltage Reference
PRODUCT DESCRIPTION
The SPX2955/56/57 is a low power voltage regulator. This device is an excellent choice for use in battery-powered applications such
as cordless telephones, radio control systems, and portable computers. The SPX2955/56/57 features very low quiescent current
(100µA Typ.) and very low dropout voltage. This includes a tight initial tolerance of 1% max and 2% max., and very low output
temperature coefficient, making the SPX2955/56/57 useful as a low-power voltage reference.
The error flag output feature is used as power-on reset for warning of a low output voltage, due to a falling voltage input of batteries.
Another feature is the logic-compatible shutdown input which enables the regulator to be switched on and off. The SPX2955/56/57 is
offered in 3-pin and 5-pin TO-220 package compatible with other 5 volt and adjustable regulators, in 8-Pin Plastic Dip SO-8 (same pin
out as SPX2951) and surface mount TO-263 packages.
The regulator output voltage (of the 8-pin package and 5-pin TO-220 & TO-263) may be pin-strapped for a 5V and 3.3V or
programmed from 1.24V to 29V with an external pair of resistors. Look for SPX2951 for 150mA and SPX2954 for 250mA
applications.
TO-263-5 Package
SPX2956/57
12 345
Top View
Five Lead Package Pin Functions:
SPX2956
SPX2957
1) ERROR
ADJUST
2) INPUT
SHUTDOWN
3) GND
GND
4) OUTPUT
INPUT
5) SHUTDOWN OUTPUT
PIN CONNECTIONS
TO-220-5 Package
SPX2956/57
8-Pin Surface Mount
OUTPUT
SENSE
SHUTDOWN
GROUND
18
2 ALPHA 7
3 SAPSX229935056
45
INPUT
FEEDBACK
5V/ 3.3V TAP
ERROR
Top View
1 2 345
Top View
TO-220-3 Package
3
2
1
Front View
VOUT
GND
VIN
TO-263-3 Package
SPX2955
Front View
3 VOUT
2 GND
1 V IN
Rev. 11/21/00
1 page  
APPLICATION HINTS
EXTERNAL CAPACITORS
The stability of the SPX2955/56/57 requires a 2.2µF or greater
capacitor between output and ground. Oscillation could occur
without this capacitor. Most types of tantalum or aluminum
electrolytic works fine here. For operations of below -25°C solid
tantalum is recommended since the many aluminum types have
electrolytes the freeze at about –30°C. The ESR of about 5Ω or
less and resonant frequency above 500kHz are the most
important parameters in the value of the capacitor. The capacitor
value can be increased without limit.
At lower values of output current, less output capacitance is
required for stability. For the currents below 10mA the value of
the capacitor can be reduced to 0.5µF and 0.15µF for 1mA. More
output capacitance needed for the 8-pin version at voltages below
5V since it runs the error amplifier at lower gain. At worst case
5µF or greater must be used for the condition of 250mA load at
1.23V output.
The SPX2955/56/57, unlike other low dropout regulators will
remain stable and in regulation with no load in addition to the
internal voltage divider. This feature is especially important in
application like CMOS RAM keep-alive. When setting the output
voltage of the SPX2955/56/57, a minimum load of 10mA is
recommended.
If there is more than 10 inches of wire between the input and the
AC filter capacitor or if a battery is used as the input then a 0.1µF
tantalum or aluminum electrolytic capacitor should be placed
from the input to the ground.
Instability can occur if there is stray capacitance to the
SPX2955/56/57 feedback terminal (pin 7). This could cause
more problems when using a higher value of external resistors to
set the output voltage.
SPX2955/56/57
This problem can be fixed by adding a 100pF capacitor between
output and feedback and increasing the output capacitor to at least
3.3µF.
ERROR DETECTION COMPARATOR OUTPUT
The Comparator produces a logic low output whenever the
SPX2955/56/57 output falls out of regulation by more than around
5%. This is around 60mV offset divided by the 1.235 reference
voltage. This trip level remains 5% below normal regardless of the
programmed output voltage of the regulator. Figure 1 shows the
timing diagram depicting the ERROR signal and the regulator output
voltage as the SPX2955/56/57 input is ramped up and down. The
ERROR signal becomes low at around 1.3V input, and goes high
around 5V input (input voltage at which Vout = 4.75). Since the
SPX2955/56/57’s dropout voltage is load dependent, the input voltage
trip point (around 5V) will vary with the load current. The output
voltage trip point (approx. 4.75V) does not vary with load.
The error comparator has an open-collector output, which requires an
external pull-up resistor. Depending on the system requirements the
resistor may be returned to 5V output or other supply voltage. In
determining the value of this resistor, note that the output is rated to
sink 400µA, this value adds to battery drain in a low battery
condition. Suggested values range from 100K to 1MΩ. If the output
is unused this resistor is not required.
PROGRAMMING THE OUTPUT VOLTAGE OF
SPX2955/56/57
The SPX2956/57 may be pin-strapped for 5V using its internal
voltage divider by tying Pin 1 (output) to Pin 2 (sense) and Pin 7
(feedback) to Pin 6 (5V Tap).
4.75V
OUTPU T
VOLTAGE
_______
ERROR*
IN PU T
VOLTAGE
+5 . 0 V
+1 . 3 V
+
+
* See A pplication Info. _ _ __ _ __
Figure 1. ER R O R O utput Tim ing
+VIN
100K
ERROR
OUTPUT
5 ______
ERROR
8
+VIN
1
VOUT
SPX2955/57
SHUTDOWN
INPUT
3
SD
GND
4
FB
7
1.23V
VREF
1.2 to 29V
+
R1 10uF
.01uF
R2
Figure 2. Adjustable Regulator
Rev. 11/21/00
5 Page | ||
| Páginas | Total 9 Páginas | |
| PDF Descargar | [ Datasheet SPX2957.PDF ] | |
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