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參數(shù)資料
| 型號(hào)： | SPX2954 |
| 元件分類： | 基準(zhǔn)電壓源/電流源 |
| 英文描述： | 250 mA Low Dropout Voltage Regulator（Output Programmable From 1.24V to 29V）(250mA，低壓差穩(wěn)壓器（可編程輸出從1.24V-29V)) |
| 中文描述： | 250毫安低壓差穩(wěn)壓器（輸出可編程從兩種器件的29V）（250mA的，低壓差穩(wěn)壓器（可編程輸出從兩種器件- 29V）） |
| 文件頁數(shù)： | 4/7頁 |
| 文件大小： | 204K |
| 代理商： | SPX2954 |
Rev. 11/21/00
SPX2954
APPLICATION HINTS
EXTERNAL CAPACITORS
For the stability of the SPX2954 requires a 2.2
μ
F 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 5
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 0.5
μ
F and 0.15
μ
F 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 5
μ
F or greater must be used for the condition of 250mA
load at 1.23V output.
The SPX2954, 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 SPX2954, a minimum load of 1
μ
A 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 1
μ
A
tantalum or aluminum electrolytic capacitor should be placed
from the input to the ground.
Instability can occur if there is stray capacitance to the SPX2954
feedback terminal (pin 7). This could cause more problems when
using a higher value of external resistors to set the output voltage.
This problem can be fixed by adding a 100pF capacitor between
output and feedback and increasing the output capacitor to at least
3.3
μ
F.
ERROR DETECTION COMPARATOR OUTPUT
The Comparator produces a logic low output whenever the SPX2954
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 SPX2954
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 V
OUT
= 4.75. Since the SPX2954’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 400
μ
A, this value adds to battery drain in a low battery
condition. Suggested values range from 100K to 1M
. If the output
is unused this resistor is not required.
PROGRAMMING
THE
OUTPUT
SPX2954
The SPX2954 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).
VOLTAGE
OF
+
+
+
+
4.75V
OUTPUT
VOLTAGE
ERROR*
_______
INPUT
VOLTAGE
1.3V
5.0V
Figure 1. ERROR Output Timing
_______
* See Application Info
.
100K
OUTPUT
ERROR
ERROR
______
SD
V
OUT
GND
FB
+V
IN
+V
IN
1.23V
1.2 to 30V
R
1
.
01uF
3.3uF
R
2
V
REF
3
8
5
1
4
7
SHUTDOWN
INPUT
+
Figure 2. Adjustable Regulator
SPX2954
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| SPX2954_05 | 制造商:SIPEX 制造商全稱:Sipex Corporation 功能描述:250mA Low Dropout Voltage Regulator |
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| SPX2954AM3-3-3 | 制造商:SIPEX 制造商全稱:Sipex Corporation 功能描述:250mA Low Dropout Voltage Regulator |
| SPX2954AM3-5.0 | 制造商:SIPEX 制造商全稱:Sipex Corporation 功能描述:250 mA Low Drop Out Voltage Regulator |
| SPX2954AM3-5-0 | 制造商:SIPEX 制造商全稱:Sipex Corporation 功能描述:250mA Low Dropout Voltage Regulator |
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