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PDF SPX2945 Data sheet ( Hoja de datos )
| Número de pieza | SPX2945 | |
| Descripción | Low Drop Out Voltage Regulator | |
| Fabricantes | Sipex | |
| Logotipo |  |
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®
SPX2945
400mA Low Dropout Voltage Regulator with Shutdown
FEATURES
■ Output 3.3V, 5.0V at 400mA Output
■ Very Low Quiescent Current, 100µA
■ Low Dropout Voltage, 420mV at 400mA
■ 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 20V
(for SO-8)
+VIN
100K
SHUTDOWN
INPUT
OFF
ON
8 +VIN
1
VOUT
SPX2945 FB 7
SD
3
______
ERROR
GND
5
4
1.2V to 20V
+
R1 0.01µF 10µF
VREF
R2
ERROR
OUTPUT
Adjustable Regulator
VIN
+
0.1 µF
IN OUT
SPX2945
GND
5V
+
2.2 µF
5V Regulator Circuit
DESCRIPTION
The SPX2945 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 SPX2945
features very low quiescent current (100µA Typ.) and very low dropout voltage. This includes a tight initial
tolerance of 1% max and very low output temperature coefficient, making the SPX2945 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 SPX2945 is offered in 3-pin TO-220 package, SO-8 (same pin
out as SPX2951), SOT-223, surface mount 3-Pin TO-252, 3-Pin TO-263 packages and 5-Pin TO-263.
The regulator output voltage (of the 8-pin SO-8) may be pin-strapped for a 3.3V and 5.0V or programmed
from 1.24V to 20V with an external pair of resistors. Look for SPX2951 for 150mA and SPX2954 for 250mA
applications.
TO-220-3 (U)
TO-263-3 (T)
TO-263-5 (T5)
TO-252 (R)
8-Pin Surface Mount(S)
SOT-223 (M3)
SPX2945
123
SPX2945
1 23
VIN GN VOU
SPX2945
5 Pin TO-263
1 2345
SPX2945
1 23
VIN GN VOU
VOU
SENS
SHUTDOWN
GN
18
SPX2945
27
36
45
VIN
FEEDBACK
5V/ 3.3V TAP
ERRO
SPX2945
1 23
VIN GN VOU
VIN GN VOU
Rev. B Date:01/20/04
SPX2945 400mA Low Dropout Voltage Regulator with Shutdown
1
©Copyright 2004 Sipex Corporation
1 page  
Error Detection Comparator Output
The Comparator produces a logic low output
whenever the SPX2945 output falls out of regu-
lation 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 SPX2945
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 = 4.75). Since the SPX2945’s
OUT
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 out-
put, which requires an external pull-up resistor.
Depending on the system requirements the re-
sistor 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
SPX2945
The SPX2945 may be pin-strapped for 5V or
3.3V using its internal voltage divider by tying
Pin 1 (output) to Pin 2 (sense) and Pin 7 (feed-
back) to Pin 6 (5V/3.3V Tap).
Also, it may be programmed for any output
voltage between its 1.235V reference and its
20V maximum rating. As seen in Figure 2, an
external pair of resistors is required.
Refer to the below equation for the program-
ming of the output voltage::
V = V x ( 1 + R / R )+ I R
OUT
REF
12
FB 1
The VREF is 1.235 and IFB is the feedback bias
current, nominally -20nA. The minimum rec-
ommended 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
SPX2945 typically draws 60 µA at no load with
Pin 2 open-circuited this is a small price to pay.
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 SPX2945 but
is relatively inefficient, as increasing the ca-
pacitor 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
C
BYPASS
≅1
/
2πR1
x
200
Hz
or choose 0.01µF. When doing this, the output
capacitor must be increased to 3.3µF to main-
tain stability. These changes reduce the output
noise from 430µV to 100µV Vrms for a 100kHz
bandwidth at 5V output. With the bypass ca-
pacitor added, noise no longer scales with out-
put voltage so that improvements are more dra-
matic at higher output voltages.
4.75V
OUTPUT
VOLTAGE
_______
ERROR*
INPUT
VOLTAGE
+5.0V
+1.3V
* See Application Info.
Figure 1. ERROR Output Timing
+
+
Rev. B Date:01/20/04
SPX2945 400mA Low Dropout Voltage Regulator with Shutdown
5
©Copyright 2004 Sipex Corporation
5 Page 
ORDERING INFORMATION
Ordering No.
SPX2945M3-3.3
SPX2945M3-5.0
SPX2945S-3.3
SPX2945S-5.0
SPX2945R-3.3
SPX2945R-5.0
SPX2945T-3.3
SPX2945T-5.0
SPX2945T5-3.3
SPX2945T5-5.0
SPX2945U-3.3
SPX2945U-5.0
Top Mark
2945M3
33YYWW
2945M3
50YYWW
2945S33
33YYWW
SPX2945R
50YYWW
SPX2945R
504YYWW
SPX2945R
YYWW
SPX2945T
33YYWW
SPX2945T5
50YYWW
SPX2945T5
33YYWW
SPX2945T
50YYWW
SPX2945U
33YYWW
SPX2945U
50YYWW
Accuracy
1%
1%
1%
1%
1%
1%
1%
1%
1%
1%
1%
1%
Output Voltage Packages
3.3V
5.0V
3.3V
5.0V
3-Pin SOT-223
3-Pin SOT-223
8-Pin SOIC
8-Pin SOIC
3.3V
3-Pin TO-252
5.0V
3-Pin TO-252
3.3V
3-Pin TO-263
5.0V
3-Pin TO-263
3.3V
5-Pin TO-263
5.0V
3.3V
5-Pin TO-263
3-Pin TO-220
5.0V
3-Pin TO-220
Corporation
ANALOG EXCELLENCE
Sipex Corporation
Headquarters and
Sales Office
233 South Hillview Drive
Milpitas, CA 95035
TEL: (408) 934-7500
FAX: (408) 935-7600
Sales Office
22 Linnell Circle
Billerica, MA 01821
TEL: (978) 667-8700
FAX: (978) 670-9001
e-mail: [email protected]
Sipex Corporation reserves the right to make changes to any products described herein. Sipex does not assume any liability arising out of the
application or use of any product or circuit described herein; neither does it convey any license under its patent rights nor the rights of others.
Rev. B Date:01/20/04
SPX2945 400mA Low Dropout Voltage Regulator with Shutdown
11
©Copyright 2004 Sipex Corporation
11 Page | ||
| Páginas | Total 11 Páginas | |
| PDF Descargar | [ Datasheet SPX2945.PDF ] | |
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