Rev. B Date:01/20/04

SPX2945 400mA Low Dropout Voltage Regulator with Shutdown

SPX2945

DESCRIPTION

FEATURES

Output 3.3V, 5.0V at 400mA Output

Very Low Quiescent Current, 100

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)

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 (100

A 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.

400mA Low Dropout Voltage Regulator with Shutdown

TO-220-3 (U)

SPX2945

5 Pin TO-263

GND

OUT

SOT-223 (M3)

SPX2945

8-Pin Surface Mount

SENS

SHUTDOWN

FEEDBACK

5V/ 3.3V TAP

ERRO

SPX2945

TO-252 (R)

SPX2945

TO-263-5

TO-263-3 (T)

SPX2945

(S)

(T5)

100K

ERROR

______

OUT

GND

0.01

SHUTDOWN
INPUT

SPX2945

OFF

REF

ERROR

OUTPUT

1.2V to 20V

2.2

SPX2945

GND

OUT

0.1

Adjustable Regulator

5V Regulator Circuit

Rev. B Date:01/20/04

SPX2945 400mA Low Dropout Voltage Regulator with Shutdown

ELECTRICAL CHARACTERISTICS

Electrical characteristics at V

= V

+1V, I

= 1mA, C

OUT

= 2.2

µF, T

= 25

°C, unless otherwise specified. The denotes

the specifications wich apply over full operating tempeture range -40

°C to +85°C, unless noted.

PARAMETER

CONDITIONS MIN TYP MAX

UNITS

(Note 2)

3.3V Version

Output Voltage

3.267 3.3 3.333 V

1mA

400mA 3.217 3.3 3.382

5.0V Version

Output Voltage

4.950 5.0 5.050 V

1mA

400mA 4.880 5.0 5.120

All Voltage Options

Output Voltage

100

ppm/

Temperature Coefficient (Note1)

Line Regulation (Note 3) 6V

20V (Note 4)

1.5

Load Regulation (Note 3) I

=1 to 400mA 6

20 mV

Dropout Voltage (Note5) I

=1mA

100 mV

150

=400mA

360 450

700

Ground Current I

=1mA

100 200

300

=150mA

4 mA

=300mA

=400mA

Current Limit V

OUT

330

800

Thermal Regulation

0.05 0.2 %/W

Output Noise,

10Hz to 100kHz,

=2.2

400

RMS

=100mA C

=33

260

PSRR at 100KHz

=100mA C

=10

Adjustable 8 Pin Version only

Reference Voltage

1.210 1.235 1.260 V

Reference Voltage Over Temperature 1.185 1.285 V

Feedback Pin Bias Current

40 nA

Reference Voltage Temp.

ppm/

Coefficient

Power Dissipation ........................................................ Internally Limited
Lead Temp. (Soldering, 5 Seconds) ............................................. 260

Storage Temperature Range ........................................ -65

C to +150

Operating Junction Temperature Range ....................... -40

C to +125

Input Supply Voltage ......................................................... -20V to +26V

ABSOLUTE MAXIMUM RATINGS

Feedback Input Voltage ................................................ -1.5V to +26V
Shutdown Input Voltage ................................................ -0.3V to +26V
Error Comparator Output .............................................. -0.3V to +26V
ESD Rating ............................................................................ 2kV Min

Rev. B Date:01/20/04

SPX2945 400mA Low Dropout Voltage Regulator with Shutdown

PARAMETER CONDITIONS MIN TYP

MAX

UNITS

(Note 2)

Feedback Pin Bieas Current

0.1

nA/

Temperature Coefficient

Output Leakage Current

=20V

0.01

Output Low Voltage

=4.5V

150

250 mV

=400

400

Upper Threshold Voltage

(Note 6) 40 60

Lower Threshold Voltage

(Note 6)

95 mV

140

Hysteresis

(Note 6)

Input Logic Voltage

Low (Regulator ON)

0.7

High (Regulator OFF)

1.3

2.0

Shutdown Pin Input Current

VS=2.4V

100

VS=26V

450

600

750

Regulator Output Current

(Note 7) 10 3

in Shutdown

ELECTRICAL CHARACTERISTICS: Continued

Electrical characteristics at V

= V

+1V, I

= 1mA, C

OUT

= 2.2

µF, T

= 25

°C, unless otherwise specified. applies over the

full operating temperature range.

Note 1: Output or reference voltage temperature coefficients defined as the worst case voltage change divided by
the total temperature range.
Note 2: Unless otherwise specified all limits are guaranteed for T

= 25

C, V

= 6V, I

= 1mA and C

= 2.2

F. Additional

conditions for the 8-pin versions are feedback tied to 5V/3.3V tap and output tied to output sense (V

OUT

= 5V) and

SHUTDOWN

0.8V.

Note 3: Regulation is measured at constant junction temperature, using pulse testing with a low duty cycle. Changes
in output voltage due to heating effects are covered under the specification for thermal regulation.
Note 4: Line regulation for the SPX2945 is tested at 150

C for I

= 1 mA. For T

= 125

C, line regulation is guaranteed

by design.
Note 5: Dropout voltage is defined as the input to output differential at which the output voltage drops 100 mV below
its nominal value measured at 1V differential at very low values of programmed output voltage, the minimum input
supply voltage of 2V ( 2.3V over temperature) must be taken into account.
Note 6: Comparator thresholds are expressed in terms of a voltage differential at the feedback terminal below the
nominal reference voltage measured at 6V input. To express these thresholds in terms of output voltage change,
multiply by the error amplifier gain = V

OUT

REF

= (R1 + R2)/R2. For example, at a programmed output voltage of 5V,

the Error output is guaranteed to go low when the output drops by 95 mV x 5V/1.235 = 384 mV. Thresholds remain
constant as a percent of V

OUT

as V

OUT

is varied, with the dropout warning occurring at typically 5% below nominal, 7.5%

guaranteed.
Note 7: V

SHUTDOWN

2V, V

26V, V

OUT

= 0, Feedback pin tied to 5V/3.3V Tap.

Rev. B Date:01/20/04

SPX2945 400mA Low Dropout Voltage Regulator with Shutdown

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

60k

330k

180k

External Capacitors

The stability of the SPX2945 requires a 2.2

µF 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

µF and 0.15µF 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

µF 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

µF 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

µF.

APPLICATION INFORMATION

Rev. B Date:01/20/04

SPX2945 400mA Low Dropout Voltage Regulator with Shutdown

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

OUT

= 4.75). Since the SPX2945'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 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
400

µA; 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 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::

OUT

= V

REF

x ( 1 + R

/ R

)+ I

The V

REF

is 1.235 and I

is the feedback bias

current, nominally -20nA. The minimum rec-
ommended load current of 1

µA forces an upper

limit of 1.2 M

on value of R

. If no load is

presented the I

produces an error of typically

2% in V

OUT

, which may be eliminated at room

temperature by trimming R

. To improve the

accuracy choose the value of R

= 100k; this

reduces the error by 0.17% and increases the
resistor program current by 12

µA. 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 1

µF to 220µF only decreases the

noise from 430

µV to 160µV Vrms for a 100kHz

bandwidth at 5V output. Noise could also be
reduced fourfold by a bypass capacitor across
R

, since it reduces the high frequency gain from

4 to unity. Pick

BYPASS

1 / 2R

x 200 Hz

or choose 0.01

µF. When doing this, the output

capacitor must be increased to 3.3

µF to main-

tain stability. These changes reduce the output
noise from 430

µV 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

1.3V

5.0V

* See Application Info.

Figure 1. ERROR Output Timing

Rev. B Date:01/20/04

SPX2945 400mA Low Dropout Voltage Regulator with Shutdown

-A-

-C-

BACK VIEW A-A

TERM 4

.010

A M

3 PLCS

-B-

SEATING
PLANE

NOTES

1. Refer To Applicable Symbol List.
2. Dimensions And Tolerancing Per Ansi Y14.5m - 1982.
3. Lead Dimension Uncontrolled in L3
4. Tab Contour Optional Within Dim. b2 & L2 And E1 & D1
5. D1 & E1 Establishes A Minimum Mounting Surface for

Terminal 4.

6. L is the Termal Length for Soldering.

7. Controlling Dimension: Inch

8. 2 Mils Suggested For Postive Contact At Mounting.

S
Y

MIN.

N
O
T
E

INCHES

MAX

MIN.

MAX

0.098

0.180

2.184
0.889
0.635
7.620
5.207
0.457
0.457
5.969
4.318
6.350
4.318

9.398
0.508
0.635
0.889
1.143

4,5

2.3876

1.143
0.889
1.143
5.461

0.5842
0.5842

6.223

6.731

10.414

1.016
1.270
1.524

A
A1
b
b1
b2
c
c1
D
D1
E
E1
e
e1
H
L
L1
L2
L3

0.086
0.035
0.025
0.300
0.205
0.018
0.018
0.235
0.170
0.250
0.170

0.370
0.020
0.025
0.035
0.045

0.094
0.045
0.035
0.045
0.215
0.023
0.023
0.245
-
0.265
-

0.410
-
0.040
0.050
0.060

2.489

4.572

PACKAGE: 3 PIN TO-252

Rev. B Date:01/20/04

SPX2945 400mA Low Dropout Voltage Regulator with Shutdown

0.408

0.013

(10.36

0.33)

0.110

0.010

(2.794

0.254)

0.250

0.010

(6.350

0.254)

0.151D

0.002

(3.835 D

0.051)

0.180

0.005

(4.572

0.127)

0.050

0.002

(1.270

0.051)

0.340

0.010

(8.636

0.254)

0.150 MIN

(3.81 MIN)

0.410

(10.41)

0.100

0.010

(2.540

0.254)

0.032

0.005

(0.813

0.127)

0.540

0.015

(13.720

0.381)

0.050 TYP

(1.27 TYP)

0.200

0.010

(5.080

0.254)

0.015

0.010/-0.002

(0.381

0.254/-0.051)

0.015

0.010/-0.015

(2.667

0.254/-0.381)

1.020

0.015

(25.910

0.381)

SEATING
PLANE

Tapered 1

2 Sides

Typ.

PACKAGE: 3 PIN TO-220

Rev. B Date:01/20/04

SPX2945 400mA Low Dropout Voltage Regulator with Shutdown

0.405 ± 0.005

(10.287 ± 0.127)

(9.042

0.127)

(15.24

0.635)

0.600

0.025

(0.813

0.076)

0.032

0.003

0.356 ± 0.005

0.055 (1.397)

0.176 ± 0.005 (4.470 ± 0.127)
0.050 ± 0.002 (1.270 ± 0.051)

0.015 +- 0.003

0° 8°

(0.381

0.074)

0.100

0.010

(2.540

0.254)

±
±

(1.702

0.127)

0.067

0.005

PACKAGE: 5 PIN TO-263

0.103 BSC

0.356

0.005

(9.042

0.127)

(15.24 0.635)

(2.616)

0.032

0.001

(0.813

0.025)

0.176 0.005
0.050 0.002

0.015

0.003

0° 8°

(0.381

0.074)

0.100

0.010

(2.540

0.254)

(4.470

0.127)

(1.270

0.051)

±
±

0.050 (1.270)

0.405 ± 0.005
(10.287 ± 0.127)

0.055 (1.397)

0.600 ± 0.025

PACKAGE: 3 PIN TO-263

Rev. B Date:01/20/04

SPX2945 400mA Low Dropout Voltage Regulator with Shutdown

Ø
Ø1

1.65

TOP VIEW

SEE VIEW C

8 PIN NSOIC

DIMENSIONS

Minimum/Maximum

(mm)

8 Pin NSOIC

(JEDEC MS-012,

AA - VARIATION)

COMMON HEIGHT DIMENSION

b
c

1.35

4.90 BSC

0.40

0.31

0.51

SYMBOL

MIN NOM MAX

0.10

0.25

1.75

1.25

0.17

0.25

6.00 BSC
3.90 BSC

1.27 BSC

1.27

1.04 REF

0.25 BSC

0º
5º

8º

15º

Ø1

Seating Plane

Gauge Plane

VIEW C

SEATING PLANE

SIDE VIEW

E/2

INDEX AREA
(D/2 X E1/2)

E1/2

WITH PLATING

BASE METAL

CONTACT AREA

PACKAGE: 8 PIN NSOIC

Rev. B Date:01/20/04

SPX2945 400mA Low Dropout Voltage Regulator with Shutdown

Corporation

ANALOG EXCELLENCE

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.

ORDERING INFORMATION

Sales Office
22 Linnell Circle
Billerica, MA 01821
TEL: (978) 667-8700
FAX: (978) 670-9001
e-mail: sales@sipex.com

Sipex Corporation

Headquarters and
Sales Office
233 South Hillview Drive
Milpitas, CA 95035
TEL: (408) 934-7500
FAX: (408) 935-7600

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