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PDF SPX3941 Data sheet ( Hoja de datos )
| Número de pieza | SPX3941 | |
| Descripción | 1A Low Drop Out Voltage Regulator | |
| Fabricantes | Sipex | |
| Logotipo |  |
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FEATURES
• Output Accuracy 3.3V, @ 1A 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
SPX3940/41/42
1A 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 SPX3940/41/42 is a low power voltage regulator. This device is an excellent choice for battery-powered applications such as
cordless telephones, radio control systems and portable computers. The SPX3940/41/42 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 SPX3940/41/42 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 SPX3940/41/42 is
offered in 3-pin and 5-pin TO-220 package SOT-223, and surface mount TO-263 packages.
The regulator output voltage (of the 8-pin SO-8 and 5-pin TO-220 & TO-263) may be pin-strapped for a 3.3V or programmed from
1.24V to 29V with an external pair of resistors.
TO-263-5 Package
SPX3941/42
12 345
Top View
Five Lead Package Pin Functions:
SPX3941 SPX3942
1) ERROR
ADJUST
2) INPUT
SHUTDOWN
3) GND
GND
4) OUTPUT
INPUT
5) SHUTDOWN OUTPUT
PIN CONNECTIONS
TO-220-5 Package
SOT-223 Package
SPX3941/42
12 345
Top View
SPX3940
123
V GND/ V
IN ADJ
OUT
Front View
TO-252 Package
3
2
1
Front View
VOUT
ADJ/GND
VIN
TO-220 Package
SPX3940
Front View
VOUT
GND/ ADJ
VIN
TO-263Package
3 VOUT
2 GND/ ADJ
Front View
1 V IN
Rev. 12/19/00
1 page  
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::
VOUT = VREF × ( 1 + R1\ R2 )+ IFBR1
The VREF is 1.235 and IFB is the feedback bias current, nominally
-20nA. The minimum recommended load current of 1 µA forces
an upper limit of 1.2 MΩ on value of R2. If no load is presented
the IFB produces an error of typically 2% in VOUT, which may be
eliminated at room temperature by trimming R1. To improve the
accuracy choose the value of R2 = 100k this reduces the error by
0.17% and increases the resistor program current by 12µA. Since
the LP2951 typically draws 60 µA at no load with Pin 2 open-
circuited this is a small price to pay
SPX3940/41/42
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 1µF to 220µF only decreases the noise
from 430µV to 160µV Vrms for a 100kHz bandwidth at 5V output.
Noise could also be reduced fourfold by a bypass capacitor across R1,
since it reduces the high frequency gain from 4 to unity. Pick
CBYPASS ≅ 1 / 2πR1 × 200 Hz
or choose 0.01µF. When doing this, the output capacitor must be
increased to 3.3µF to maintain stability. These changes reduce the
output noise from 430µV to 100µV 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.
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:
PTOTAL = (VIN - 5) IL + (VIN)IG
Next step is to calculate the temperature rise TR (max). TJ (max)
maximum allowable junction temperature, TA (max) maximum
ambient temperature :
TR (max) = TJ (max) - TA (max)
Junction to ambient thermal resistance θ(j-A) can be calculated
after determining of PTOTAL & TR (max):
θ(J-A) = TR (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)
IIN
VIN
+
IIN = IL + IG
IN OUT
SPX3940
GND
IG
3.3V
+
2.2 uF
Figure 3. 3.3V Regulator Circuit
IL
LOAD
Rev. 12/19/00
5 Page | ||
| Páginas | Total 7 Páginas | |
| PDF Descargar | [ Datasheet SPX3941.PDF ] | |
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