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參數(shù)資料
| 型號(hào)： | SPX2947S |
| 英文描述： | 500mA Low Drop Out Voltage Regulator with Shutdown |
| 中文描述： | 500mA的低壓差與關(guān)斷穩(wěn)壓器 |
| 文件頁(yè)數(shù)： | 6/11頁(yè) |
| 文件大?。?/td> | 101K |
| 代理商： | SPX2947S |
4
Rev. B Date:01/20/04
SPX2945 400mA Low Dropout Voltage Regulator with Shutdown
Copyright 2004 Sipex Corporation
SPX2945 - 5.0V BLOCK DIAGRAM
FEEDBACK
INPUT
OUTPUT
UNREGULATED DC
SHUTDOWN
GROUND
ERROR
______
5V TAP
SENSE
5V at 400mA
MAX
TO CMOS OR
TTL
REFERENCE
ERROR DETECTION
COMPARATOR
ERROR
AMPLIFIER
1.23V
FROM
CMOS OR
TTL
+
60 mV
3
7
8
1
2
6
5
4
.
60k
330k
180k
.
1F
_
External Capacitors
The stability of the SPX2945 requires a 2.2
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 that 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 capaci-
tor. The capacitor value can be increased with-
out 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
F and 0.15F 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
4.7
F or greater must be used for the condition
of 250mA load at 1.23V output.
The SPX2945, unlike other low dropout regu-
lators will remain stable and in regulation with
no load in addition to the internal voltage di-
vider. This feature is especially important in
applications like CMOS RAM keep-alive.
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 0.1
F tanta-
lum or aluminum electrolytic capacitor should
be placed from the input to the ground.
Instability can occur if there is stray capaci-
tance to the SPX2945 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
F.
APPLICATION INFORMATION
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