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參數(shù)資料
| 型號： | SPX3940 |
| 英文描述： | 1A Low Drop Out Voltage Regulator |
| 中文描述： | 1A低壓降穩(wěn)壓器 |
| 文件頁數(shù)： | 5/7頁 |
| 文件大?。?/td> | 169K |
| 代理商： | SPX3940 |
Rev. 12/19/00
SPX3940/41/42
Also, it may be programmed for any output voltage between its
1.235V reference and its 30V maximum rating. As seen in
Figure 2, an external pair of resistors is required.
Refer to the below equation for the programming of the output
voltage::
V
OUT
= V
REF
×
( 1 + R
1
\ R
2
)+ I
FB
R
1
The V
REF
is 1.235 and I
FB
is the feedback bias current, nominally
-20nA. The minimum recommended load current of 1
μ
A forces
an upper limit of 1.2 M
on value of R
2
.
If no load is presented
the I
FB
produces an error of typically 2% in V
OUT
, which may be
eliminated at room temperature by trimming R
1
. To improve the
accuracy choose the value of R2 = 100k this reduces the error by
0.17% and increases the resistor program current by 12
μ
A. Since
the LP2951 typically draws 60
μ
A at no load with Pin 2 open-
circuited this is a small price to pay
HEAT SINK REQUIREMENTS
Depending on the maximum ambient temperature and maximum
power dissipation a heat sink may be required with the
SPX3940/41/42. The junction temperature range has to be within
the range specified under Absolute Maximum Ratings under all
possible operating conditions. To find out if a heat sink is
required, the maximum power dissipation of the device needs to
be calculated. This is the maximum specific AC voltage that
must be taken into consideration at input. Figure 3 shows the
condition and power dissipation which should be calculated with
the following formula:
P
TOTAL
= (V
IN
- 5) I
L
+ (V
IN
)I
G
Next step is to calculate the temperature rise T
R
(max). T
J
(max)
maximum allowable junction temperature, T
A
(max) maximum
ambient temperature :
T
R
(max) = T
J
(max) - T
A
(max)
Junction to ambient thermal resistance
θ
(j-A)
can be calculated
after determining of P
TOTAL &
T
R
(max):
θ
(J-A)
= T
R
(max)/P
(max)
If the
θ
(J-A)
is 60
°
C/W or higher, the device could be operated
without a heat sink. If the value is below 60
°
C/W then the heat
sink is required and the thermal resistance of the heat sink can be
calculated by the following formula,
θ
(J-C)
junction to case,
θ
(C-H)
case to heat sink,
θ
(H-A)
heat sink to ambient:
θ
(J-A)
=
θ
(J-C)
+
θ
(C-H)
+
θ
(H-A)
REDUCING OUTPUT NOISE
It may be an advantage to reduce the AC noise present at the output.
One way is to reduce the regulator bandwidth by increasing the size of
the output capacitor. This is the only way that noise can be reduced
on the 3 lead SPX3940/41/42 but is relatively inefficient, as
increasing the capacitor from 1
μ
F to 220
μ
F only decreases the noise
from 430
μ
V to 160
μ
V Vrms for a 100kHz bandwidth at 5V output.
Noise could also be reduced fourfold by a bypass capacitor across R
1
,
since it reduces the high frequency gain from 4 to unity. Pick
C
BYPASS
1 / 2
π
R
1
×
200 Hz
or choose 0.01
μ
F. When doing this, the output capacitor must be
increased to 3.3
μ
F to maintain stability. These changes reduce the
output noise from 430
μ
V to 100
μ
V Vrms for a 100kHz bandwidth at
5V output. With the bypass capacitor added, noise no longer scales
with output voltage so that improvements are more dramatic at higher
output voltages.
+
2.2 uF
+
SPX3940
I
IN
V
IN
I
G
I
L
3.3V
IN
OUT
GND
LOAD
I
IN
= I
L
+ I
G
Figure 3. 3.3V Regulator Circuit
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相關(guān)代理商/技術(shù)參數(shù) |
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|---|---|
| SPX3940_12 | 制造商:EXAR 制造商全稱:EXAR 功能描述:1A Low Dropout Voltage Regulator |
| SPX3940AM3 | 制造商:SIPEX 制造商全稱:Sipex Corporation 功能描述:1A Low Drop Out Voltage Regulator |
| SPX3940AM3-1.8 | 制造商:SIPEX 制造商全稱:Sipex Corporation 功能描述:1A Low Dropout Voltage Regulator Fixed Output, Fast Response |
| SPX3940AM3-1.8/ | 制造商:SIPEX 制造商全稱:Sipex Corporation 功能描述:1A Low Dropout Voltage Regulator Fixed Output, Fast Response |
| SPX3940AM3-2.5 | 制造商:SIPEX 制造商全稱:Sipex Corporation 功能描述:1A Low Dropout Voltage Regulator Fixed Output, Fast Response |
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