Input Can Withstand -20V Reverse Battery & +60 Positive Transient
PRODUCT DESCRIPTION
The AS2954 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 AS2954 features very low quiescent current (75µA Typ.) and
very low dropout voltage. This includes a tight initial tolerance of
±
0.5% max and
±
1% max., and very low output temperature
coefficient, making the AS2954 useful as a low-power voltage reference. The key AS2954 features include protection against reversed
battery, fold-back current limiting, and automotive load dump protection (60V positive transient).
The error flag output feature is used as power-on reset for warning of a low output voltage, due to falling voltage input of batteries.
Another feature is the logic compatible shutdown input which enables the regulator to be switched on and off. The AS2954 is offered
in a 3-pin TO-92and TO-263 package compatible with other 5 volt regulators, in 8-Pin plastic, SO-8, (same pin out as AS2951), TO-
220 and TO-263.
The regulator output voltage (of the 8-pin) may be pin-strapped for a 5Vand 3.3V or programmed from 1.24V to 29V with an external
pair of resistors. Look for AS2951 for 150mA and LP2951 for 100mA applications.
PIN CONNECTIONS
TO-263-3 Package
TO-263-5 Package
8-Pin Surface Mount (S)
OUTPUT
1
2
3
4
AS2954
8
7
6
5
INPUT
FEEDBACK
5V, 3.3V TAP
ERROR
1
SOT-223 Package
TO-220-3 Package
TO-220-5 Package
AS2954
1
2
3
AS2954
1 2 3 4 5
1) INPUT
2)
3)
4)
5)
OUTPUT
GND
SHUTDOWN
ERROR
SENSE
SHUTDOWN
GND
AS2954
2
3
AS2954
AS2954
1) INPUT
2) OUTPUT
Top View
TO-92 (N)
1
2
3
V
IN
GND
V
OUT
3) GND
4) SHUTDOWN
5) ERROR
1 2 3
V
IN
GND V
OUT
1 2 3 4 5
Front View
V
ADJ
V
OUT
V
IN
Top View
Top View
Front View
OUTPUT
GND
INPUT
Front View
Bottom View
Rev.9/29/00
AS2954
ORDERING INFORMATION
TO-263
3-PIN
AS2954YT3-X
TO-263
5-PIN
AS2954YT5-X
TO-92
3 PIN
AS2954YN-X
TO-220
3 PIN
AS2954YU3-X
TO-220
5 PIN
AS2954YU5-X
PLASTIC SOIC
8 PIN
AS2954YS-X
SOT-223
3 PIN
AS2954YM3-X
OPER.TEMP.
RANGE
-40°C to +125°C
X= Output Voltage: (3.3 for 3.3V, 5.0 for 5.0V)
Y= Output Tolerance (A = 0.5%, Blank = 1%; B = 2%)
ABSOLUTE MAXIMUM RATINGS
Power Dissipation..........................................Internally Limited
Lead Temp. (Soldering, 5 Seconds) ................................ 260°C
Storage Temperature Range ............................ -65° to +150°C
Operating Junction Temperature Range (Note 9)
AS2954 .................................................. -40C° to +125°C
Input Supply Voltage .......................................-20V to +60V
Feedback Input Voltage .....................................-1.5 to +30V
Shutdown Input Voltage.....................................-0.3 to +30V
Error Comparator Output ...................................-0.3 to +30V
ESD Rating ............................................................ 2KV Min
ELECTRICAL CHARACTERISTICS
at V
S
=±15V, T
A
=25°C
,
unless otherwise noted.
Boldface
applies over the full
operating temperature range.
Parameter
3.3V Version
Output Voltage
Conditions
Typical
AS2954A
Min Max
3.284
3.267
3.260
3.251
3.317
3.333
3.340
3.350
AS2954
Min
Max
3.267
3.251
3.234
3.201
3.333
3.350
3.366
3.399
AS2954B
Min
Max
3.234
3.201
3.194
3.168
3.366
3.399
3.432
3.432
Units
Output Voltage
5V Version
Output Voltage
T
J
=25°C
-25°C
≤
T
J
≤
+85°C
-40°C
≤
T
J
≤
+125°C
1mA
≤I
L
≤
250mA
T
J
≤T
JMAX
T
J
=25°C
-25°C
≤
T
J
≤
+85°C
-40°C
≤
T
J
≤
+125°C
1mA
≤I
L
≤
250mA
T
J
≤T
JMAX
3.3
V
3.3
V
Output Voltage
All Voltage Options
Output Voltage
Temperature Coefficient
Line Regulation (Note 3)
Load Regulation (Note 3)
Dropout Voltage
(Note 5)
5.0
5.0
5.0
5.0
4.975
4.95
4.94
4.925
5.025
5.050
5.06
5.075
4.95
4.925
4.90
4.85
5.05
5.075
5.10
5.15
4.90
4.85
4.84
4.80
5.10
5.15
5.20
5.20
V
V
20
(Note 1)
6V
≤V
IN
≤30V
(Note 4)
I
L
= 1 to 250 mA
I
L
= 0.1 to 1 mA
I
L
= 1mA
I
L
= 50mA
I
L
= 100mA
I
L
= 250 mA
0.03
0.04
60
220
250
375
90
1
4.5
21
100
0.10
0.20
0.16
0.20
100
150
250
420
300
450
450
600
150
180
2
2.5
6
8
14
16
550
600
0.2
150
0.20
0.40
0.20
0.30
100
150
250
420
300
450
450
600
150
180
2
2.5
6
8
20
22
550
600
0.2
180
0.40
0.60
0.30
0.40
100
150
250
420
300
450
450
600
150
180
2
2.5
6
8
26
28
550
600
0.2
ppm/°C
%max
%max
mV
Ground Current
I
L
= 1mA
I
L
= 50mA
I
L
= 100mA
I
L
= 250 mA
µA
mA
Current Limit
Thermal Regulation
Output Noise,
10Hz to 100khz
I
L
= 100mA
8-Pin Versions only
Reference Voltage
Reference Voltage
Feedback Pin Bias Current
Reference Voltage Temperature
Coefficient
Feedback Pin Bias Current
Temperature Coefficient
V
OUT
= 0
0.05
C
L
= 2.2µF
C
L
= 33
µF
400
260
Typical
1.235
mA
%/w
µV
rms
Over Temperature (Note 6)
20
AS2954A
1.220
1.250
1.200
1.260
1.190
1.27
40
60
AS2954
1.210
1.200
1.185
1.260
1.270
1.285
40
60
AS2954B
1.200
1.270
1.190
1.280
1.180
1.295
40
60
V
V
nA
ppm/°C
(Note 7)
50
nA/°C
0.1
Rev.9/29/00
AS2954
(Continued)
Parameter
Conditions
(Note 2)
Typical
AS2954A
Min
Max
AS2954
Min
Max
AS2954B
Min
Max
Units
Applies for AS2954YT5-X, AS2954YU5-X and AS2954YS-X
Error Comparator
Output Leakage Current
Output Low Voltage
Upper Threshold Voltage
Lower Threshold Voltage
Hysteresis
Shutdown Input
V
SD
Hysteresis(HYST)
Input Bias Current(I
B
)
V
IN(SD)
= 0V to 5V
V
OH
= 30V
V
IN
= 4.5V
I
OL
= 400µA
(Note 8)
(Note 8)
(Note 8)
0.01
150
240
350
60
-320
-380
-450
-640
100
2.00
250
400
-150
-100
230
160
-320
-380
-450
-640
100
2.00
250
400
-150
-100
230
160
-320
-380
-450
-640
100
2.00
250
400
-150
-100
230
160
µA
mV
mV
mV
mV
Output Turn-On
Threshold Voltage
6
10
1.155
1.140
1.305
1.320
1.155
1.140
1.305
1.320
1.155
1.140
1.305
1.320
V
mV
nA
-30
-50
-30
-50
-30
-50
-30
-50
-30
-50
-30
-50
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
= 100
µA
and C
L
= 1µF. Additional conditions for the 8-pin versions are
feedback tied to 5V 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 AS2954 is tested at 150°C for I
L
= 1 mA. For I
L
= 100µA and T
J
= 125°C, line regulation is guaranteed by design to 0.2%. See typical
performance characteristics for line regulation versus temperature and load current.
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:
V
REF
≤V
OUT
≤
(V
IN
- 1V), 2.3
≤V
IN
≤30V,
100µA≤I
L
≤
250 mA, T
J
≤
T
JMAX
.
Note 7:
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
= (R
1
+ R
2
)/R
2
. 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 8:
V
SHUTDOWN
≥
2V, V
IN
≤
30V, V
OUT
=0, feedback pin tied to 5V Tap.
Note 9:
The junction -to-ambient thermal resistance of the TO-92 package is 180°C/ W with 0.4” leads and 160°C/ W with 0.25” leads to a PC board.
The thermal resistance of the 8-Pin DIP package is 105°C/W junction-to-ambient when soldered directly to a PC board. Junction-to-ambient thermal resistance for the
SOIC (S) package is 160°C/W.
UNREGULATED DC
7
FEEDBACK
8
INPUT
1
OUTPUT
2
SENSE
+
_
FROM
CMOS OR
TTL
3
SHUTDOWN
60k
Ω
..
180k
Ω
..
6
ERROR
AMPLIFIER
5V TAP
+
1
µ
F
..
V
O
5V @ 250mA
MAX
+
330k
Ω
..
+
60 mV
+ 1.23V
+
_
ERROR
COMPARATOR
5
______
ERROR
TO CMOS OR
TTL
4
REFERENCE
GROUND
AS2954 Block Diagram
Rev.9/29/00
AS2954
APPLICATION HINTS
EXTERNAL CAPACITORS
For the stability of the AS2954 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 the 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 capacitor. The capacitor
value can be increased without 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 5µF or greater must be used for the condition of 250mA
load at 1.23V output.
The AS2954, unlike other low dropout regulators will remain
stable and in regulation with no load in addition to the internal
voltage divider.
This feature is especially important in
application like CMOS RAM keep-alive. When setting the
output voltage of the AS2954, a minimum load of 1µA is
recommended
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 1µA
tantalum or aluminum electrolytic capacitor should be placed
from the input to the ground.
Instability can occur if there is stray capacitance to the AS2954
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.
ERROR DETECTION COMPARATOR OUTPUT
The Comparator produces a logic low output whenever the AS2954
output falls out of regulation 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 AS2954
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 AS2954’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 output, which requires an
external pull-up resistor. Depending on the system requirements the
resistor 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 AS2954
The AS2954 may be pin-strapped for 5V using its internal voltage
divider by tying Pin 1 (output) to Pin 2 (sense) and Pin 7 (feedback)
to Pin 6 (5V Tap).
+V
IN
4.75V
100K
OUTPUT
VOLTAGE
_______
ERROR*
ERROR
OUTPUT
5
______
ERROR
8
+V
IN
V
OUT
1
1.2 to 30V
AS2954
SHUTDOWN
INPUT
3
SD
GND
4
FB
7
1.23V
R
1
.01uF
+
3.3uF
+
5.0V
INPUT
VOLTAGE
+
1.3V
+
+
V
REF
R
2
* See Application Info
.
_______
Figure 1. ERROR Output Timing
Figure 2. Adjustable Regulator
Rev.9/29/00
AS2954
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 1µA 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 LP2951 typically draws 60µA 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 AS2954 but is relatively inefficient, as increasing the
capacitor from 1µF to 220µF only decreases the noise from 430µV to
160µV rms 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
×
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
RMS
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.
HEATSINK REQUIREMENTS
Depending on the maximum ambient temperature and maximum
power dissipation a heatsink may be required with the AS2954.
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 heatsink 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 heatsink. If the value is below 60°C/W then the
heatsink is required and the thermal resistance of the heatsink can
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