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)
0.1
µF
ON
SHUTDOWN
INPUT
OFF
+V
IN
100K
8
+V
IN
1
V
OUT
1.2V to 20V
+
SPX2945
3
SD
GND
4
FB
7
R
1
0.01µF
10µF
______
ERROR
ERROR
5
R
2
V
REF
OUTPUT
Adjustable Regulator
V
IN
5V
IN
OUT
SPX2945
+
GND
+
2.2
µF
5V Regulator Circuit
Now Available in Lead Free Packaging
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)
V
OU
8-Pin Surface Mount
(S)
SOT-223 (M3)
SPX2945
SPX2945
1
1
2
3
2
3
1
2
3
4
8
7
6
5
SPX2945
5 Pin TO-263
SPX2945
1
2
3
SPX2945
SENS
SHUTDOWN
V
IN
FEEDBACK
5V/ 3.3V TAP
ERRO
SPX2945
1
2
3
1 2 3 4 5
V
IN
GN
V
IN
GN
V
OU
V
OU
GN
V
IN
GN
V
OU
V
IN
GN
V
OU
Note: Tab is Ground
Date: 3/14/06
SPX2945 400mA Low Dropout Voltage Regulator with Shutdown
©Copyright 2006 Sipex Corporation
GND
V
OUT
V
IN
SD
Er
1
ABSOLUTE MAXIMUM RATINGS
Power Dissipation ........................................................ Internally Limited
Lead Temp. (Soldering, 5 Seconds) ............................................. 260°C
Storage Temperature Range ........................................ -65°C to +150°C
Operating Junction Temperature Range ....................... -40°C to +125°C
Input Supply Voltage ......................................................... -20V to +26V
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
ELECTRICAL CHARACTERISTICS
Electrical characteristics at V
IN
= V
O
+1V, I
O
= 1mA, C
OUT
= 2.2µF, T
A
= 25°C, unless otherwise specified.
The
♦
denotes
the specifications wich apply over full operating tempeture range -40°C to +85°C, unless noted.
PARAMETER
3.3V Version
Output Voltage
1mA
≤
I
L
≤
400mA
5.0V Version
Output Voltage
1mA
≤
I
L
≤
400mA
All Voltage Options
Output Voltage
Temperature Coefficient
Line Regulation (Note 3)
Load Regulation (Note 3)
Dropout Voltage (Note5)
20
(Note1)
6V
≤
V
IN
≤
20V (Note 4)
I
L
=1 to 400mA
I
L
=1mA
I
L
=400mA
Ground Current
I
L
=1mA
I
L
=150mA
I
L
=300mA
I
L
=400mA
Current Limit
Thermal Regulation
Output Noise,
10Hz to 100kHz,
I
L
=100mA
PSRR at 100KHz
I
L
=100mA
Reference Voltage
Reference Voltage
Feedback Pin Bias Current
Reference Voltage Temp.
Coefficient
Date: 3/14/06
CONDITIONS
(Note 2)
MIN
TYP
MAX
UNITS
3.267
3.217
4.950
4.880
3.3
3.3
5.0
5.0
3.333
3.382
5.050
5.120
100
♦
V
V
♦
♦
♦
♦
mV
♦
♦
µA
♦
mA
♦
♦
♦
♦
mA
%/W
µV
RMS
dB
ppm/°C
mV
mV
1.5
6
60
360
100
2
4
8
330
0.05
400
260
31
20
20
30
100
150
450
700
200
300
4
6
8
12
15
25
800
0.2
V
OUT
=0
C
L
=2.2µF
C
L
=33µF
C
L
=10µF
1.210
Over Temperature
1.185
Adjustable 8 Pin Version only
1.235
20
20
1.260
1.285
40
60
♦
ppm/°C
V
V
nA
SPX2945 400mA Low Dropout Voltage Regulator with Shutdown
©Copyright 2006 Sipex Corporation
2
ELECTRICAL CHARACTERISTICS: Continued
Electrical characteristics at V
IN
= V
O
+1V, I
O
= 1mA, C
OUT
= 2.2µF, T
A
= 25°C, unless otherwise specified.
♦
applies over the
full operating temperature range.
PARAMETER
Feedback Pin Bieas Current
Temperature Coefficient
Output Leakage Current
Output Low Voltage
Upper Threshold Voltage
Lower Threshold Voltage
Hysteresis
Input Logic Voltage
Shutdown Pin Input Current
V
0H
=20V
V
IN
=4.5V
I
0L
=400µA
(Note 6)
(Note 6)
(Note 6)
Low (Regulator ON)
High (Regulator OFF)
VS=2.4V
VS=26V
Regulator Output Current
in Shutdown
Thermal Resistance
Theta Junction-Ambient
θ
JA
(Note 7)
TO-220-3
TO-263-3
TO-263-5
NSOIC-8
SOT-223
TO-252
10
20
40
25
60
75
15
1.3
30
450
3
♦
29.4
31.4
31.2
128.4
62.3
50
♦
♦
♦
♦
♦
♦
°C/W
0.7
2.0
50
100
600
750
♦
♦
♦
♦
µA
95
140
CONDITIONS
(Note 2)
MIN
TYP
0.1
0.01
150
1
2
250
400
♦
mV
mV
♦
mV
V
µA
♦
mV
MAX
♦
UNITS
nA/°C
µA
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
j
= 25°C, V
IN
= 6V, I
L
= 1mA and C
L
= 2.2µF. 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
V
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
L
= 1 mA. For T
J
= 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
/V
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
IN
≤
26V, V
OUT
= 0, Feedback pin tied to 5V/3.3V Tap.
Date: 3/14/06
SPX2945 400mA Low Dropout Voltage Regulator with Shutdown
©Copyright 2006 Sipex Corporation
3
SPX2945 - 5.0V BLOCK DIAGRAM
UNREGULATED DC
7
FEEDBACK
+
8
INPUT
1
OUTPUT
5V at 400mA
MAX
2
SENSE
+
_
FROM
CMOS OR
TTL
3
SHUTDOWN
180kΩ
ERROR
AMPLIFIER
.
6
5V TAP
330kΩ
.
+
5
______
ERROR
1µF
TO CMOS OR
TTL
4
60kΩ
.
+
60 mV
+ 1.23V
+
_
ERROR DETECTION
COMPARATOR
REFERENCE
GROUND
APPLICATION INFORMATION
External Capacitors
The stability of the SPX2945 requires a 2.2µF 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 5Ω 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 0.5µF 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
4.7µF 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 0.1µF 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 3.3µF.
Date: 3/14/06
SPX2945 400mA Low Dropout Voltage Regulator with Shutdown
©Copyright 2006 Sipex Corporation
4
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
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
OUT
= V
REF
x ( 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 rec-
ommended load current of 1
µA
forces an upper
limit of 1.2 MΩ 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 R
2
= 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
R
1
, since it reduces the high frequency gain from
4 to unity. Pick
C
BYPASS
≅1
/ 2πR
1
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*
+
5.0V
INPUT
VOLTAGE
+
+
+
1.3V
* See Application Info.
Figure 1. ERROR Output Timing
Date: 3/14/06
SPX2945 400mA Low Dropout Voltage Regulator with Shutdown
©Copyright 2006 Sipex Corporation
5
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