Advanced Monolithic Systems, Inc. 6680B Sierra Lane, Dublin, CA 94568 Phone (925) 556-9090 Fax (925) 556-9140
Advanced AMS2950/AMS2951
Monolithic 150mA LOW DROPOUT VOLTAGE REGULATOR
Systems
FEATURES APPLICATIONS
•• 5.0V, 3.3V, 3.0V and 2.5V Versions •• Battery Powered Systems
•• High Accuracy Output Voltage •• Portable Consumer Equipment
•• Extremely Low Quiescent Current •• Cordless Telephones
•• Low Dropout Voltage •• Portable (Notebook) Computers
•• Extremely Tight Load and Line Regulation •• Portable Instrumentation
•• Very Low Temperature Coefficient •• Radio Control Systems
•• Current and Thermal Limiting •• Automotive Electronics
•• Needs Minimum Capacitance (1µµF) for Stability •• Avionics
•• Unregulated DC Positive Transients 60V •• Low-Power Voltage Reference
ADDITIONAL FEATURES (AMS2951 ONLY)
•• 1.24V to 29V Programmable Output
•• Error Flag Warning of Voltage Output Dropout
•• Logic Controlled Electronic Shutdown
GENERAL DESCRIPTION
The AMS2950 and AMS2951 are micropower voltage regulators ideally suited for use in battery-powered systems. These
devices feature very low quiescent current (typ.75µA), and very low dropout voltage (typ.45mV at light loads and 380mV at
150mA) thus prolonging battery life. The quiescent current increases only slightly in dropout. The AMS2950/AMS2951 has
positive transient protection up to 60V and can survive unregulated input transient up to 20V below ground.
The AMS2950 and AMS2951 were designed to include a tight initial tolerance (typ. 0.5%), excellent load and line regulation
(typ. 0.05%), and a very low output voltage temperature coefficient, making these devices useful as a low-power voltage
reference.
The AMS2950 is offered in the 3-pin TO-92 package. AMS2951 is available in 8-pin plastic SOIC and DIP packages and
offers three major additional system features. An error flag output warns of a low output voltage, often due to failing batteries
on input. The AMS2951 also features the logic-compatible shutdown input which enables the regulator to be switched on and
off. The AMS2951 device may be pin-strapped for a 5.0V, 3.3V, 3.0V or 2.5 output, or programmed from 1.24V to 29V with
an external pair of resistors.
ORDERING INFORMATION PIN CONNECTION
PACKAGE TYPE
OPERATING
TO-92
8 LEAD PDIP
8 LEAD SOIC
TEMP. RANGE
AMS2950ACN-X
AMS2951ACP-
AMS2951ACS-X
IND.
AMS2950CN-X
AMS2951CP-X
AMS2951CS-X
IND
X = 3.3V, 3.0V, 2.5V
8L SOIC/ 8L PDIP
1
2
8
4
3
7
5
6VTAP
ERROR
FEEDBACK
OUTPUT
SENSE
SHUTDOWN
INPUT
GROUND
Top View
TO-92
OUTPUT INPUT
GND
Bottom View
Advanced Monolithic Systems, Inc. 6680B Sierra Lane, Dublin, CA 94568 Phone (925) 556-9090 Fax (925) 556-9140
AMS2950/AMS2951
ABSOLUTE MAXIMUM RATINGS (Note 1)
Input Supply Voltage -0.3 to +30V Wave 4 seconds, 260°C
SHUTDOWN Input Voltage, Infrared 4 seconds, 240°C
Error Comparator Output Vapor Phase 4 seconds, 219°C
Voltage,(Note 9) ESD TBD
FEEDBACK Input Voltage -1.5 to +30V
(Note 9) (Note 10) OPERATING RATINGS (Note 1)
Power Dissipation
Internally Limited
Junction Temperature +150°C Max. Input Supply Voltage 30V
Storage Temperature -65
°
C to +150
°
CJunction Temperature Range
Soldering Dwell Time, Temperature (TJ) (Note 8)
AMS2950AC-XX,
AMS2950C-XX
AMS2951AC-XX,
AMS2951C-XX -40°C to +125°C
ELECTRICAL CHARACTERISTICS at Vs=Vout+1V, Ta=25°C, unless otherwise noted.
Parameter Conditions
(Note 2)
AMS2950AC
AMS2951AC
Min. Typ. Max.
AMS2950C
AMS2951C
Min. Typ. Max. Units
2.5 V Versions (Note 16)
Output Voltage TJ = 25°C (Note 3)
-25°C ≤TJ ≤85°C
Full Operating Temperature
Range
2.488
2.475
2.470
2.5
2.5
2.5
2.512
2.525
2.530
2.475
2.450
2.440
2.5
2.5
2.5
2.525
2.550
2.560
V
V
V
Output Voltage 100 µA ≤IL ≤150 mA
TJ ≤TJMAX 2.463 2.5 2.537 2.448 2.5 2.562 V
3.0 V Versions (Note 16)
Output Voltage TJ = 25°C (Note 3)
-25°C ≤TJ ≤85°C
Full Operating Temperature
Range
2.985
2.970
2.964
3.0
3.0
3.0
3.015
3.030
3.036
2.970
2.955
2.940
3.0
3.0
3.0
3.030
3.045
3.060
V
V
V
Output Voltage 100 µA ≤IL ≤150 mA
TJ ≤TJMAX 2.958 3.0 3.042 2.928 3.0 3.072 V
3.3 V Versions (Note 16)
Output Voltage TJ = 25°C (Note 3)
-25°C ≤TJ ≤85°C
Full Operating Temperature
Range
3.284
3.267
3.260
3.3
3.3
3.3
3.317
3.333
3.340
3.267
3.251
3.234
3.3
3.3
3.3
3.333
3.350
3.366
V
V
V
Output Voltage 100 µA ≤IL ≤150 mA
TJ ≤TJMAX 3.254 3.3 3.346 3.221 3.3 3.379 V
5.0 V Versions (Note 16)
Output Voltage TJ = 25°C (Note 3)
-25°C ≤TJ ≤85°C
Full Operating Temperature
Range
4.975
4.95
4.94
5.0
5.0
5.0
5.025
5.050
5.06
4.95
4.925
4.90
5.0
5.0
5.0
5.05
5.075
5.10
V
V
V
Output Voltage 100 µA ≤IL ≤150 mA
TJ ≤TJMAX 4.925 5.0 5.075 4.88 5.0 5.12 V
All Voltage Options
Output Voltage
Temperature Coefficient (Note 12) (Note 4) 20 50 ppm/°C
Line Regulation (Note 14) 6V ≤Vin ≤30V (Note 15) 0.03 0.1 0.04 0.2 %
Load Regulation (Note 14) 100 µA ≤IL ≤ 150 mA 0.04 0.1 0.1 0.2 %
Advanced Monolithic Systems, Inc. 6680B Sierra Lane, Dublin, CA 94568 Phone (925) 556-9090 Fax (925) 556-9140
AMS2950/AMS2951
ELECTRICAL CHARACTERISTICS (Note 2) (Continued)
PARAMETER CONDITIONS
(Note 2)
AMS2950AC
AMS2951AC
Min. Typ. Max.
AMS2950C
AMS2951C
Min. Typ. Max. Units
Dropout Voltage
(Note 5)
IL = 100µ A
IL = 150 mA 50
380
80
450
50
380
80
450
mV
mV
Ground Current IL = 100 µA
IL = 150 mA 75
8
120
12
75
8
120
12
µA
mA
Current Limit Vout = 0 160 200 160 200 mA
Thermal Regulation (Note 13) 0.05 0.2 0.05 0.2 %/W
Output Noise,
10Hz to 100KHz
CL = 1µF
CL = 200 µF
CL = 13.3 µF
(Bypass = 0.01 µF pins 7 to
1(AMS2951))
430
160
100
430
160
100
µV rms
µV rms
µV rms
8-Pin Versions only AMS2951AC AMS2951C
Reference Voltage 1.22 1.235 1.25 1.21 1.235 1.26 V
Reference Voltage Over Temperature (Note 7) 1.19 1.27 1.185 1.285 V
Feedback Pin Bias Current 40 60 40 60 nA
Reference Voltage Temperature
Coefficient ( Note 12 ) 20 50 ppm/°C
Feedback Pin Bias Current
Temperature Coefficient 0.1 0.1 nA/°C
Error Comparator
Output Leakage Current VOH = 30V 0.01 10.01 1µA
Output Low Voltage Vin = 4.5V
IOL = 400µA150 250 150 250 mV
Upper Threshold Voltage (Note 6) 40 60 40 60 mV
Lower Threshold Voltage (Note 6) 75 95 75 95 mV
Hysteresis (Note 6) 15 15 mV
Shutdown Input
Input logic Voltage Low (Regulator ON)
High (Regulator OFF) 21.3 0.7 21.3 0.7 V
V
Shutdown Pin Input Current
(Note 3) Vs = 2.4V
Vs = 30V 30
450
50
600
30
450
50
600 µA
µA
Regulator Output Current in
Shutdown (Note 3) (Note 11) 3 10 3 10 µA
Note 1: Absolute Maximum Ratings are limits beyond which damage to the device may occur. Operating Ratings are conditions under which operation of the
device is guaranteed. Operating Ratings do not imply guaranteed performance limits. For guaranteed performance limits and associated test conditions, see the
Electrical Characteristics tables.
Note 2: Unless otherwise specified all limits guaranteed for VIN = ( VONOM +1)V, IL = 100 µA and CL = 1 µF for 5V versions and 2.2µF for 3V and 3.3V
versions. Limits appearing in boldface type apply over the entire junction temperature range for operation. Limits appearing in normal type apply for TA = TJ =
25°C Additional conditions for the 8-pin versions are FEEDBACK tied to VTAP, OUTPUT tied to SENSE and VSHUTDOWN ≤ 0.8V.
Note 3: Guaranteed and 100% production tested.
Note 4: Guaranteed but not 100% production tested. These limits are not used to calculate outgoing AQL levels.
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
VIN = ( VONOM +1)V. To express these thresholds in terms of output voltage change, multiply by the error amplifier gain = Vout/Vref = (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 Vout as Vout is varied, with the dropout warning occurring at typically 5% below nominal, 7.5% guaranteed.
Note 7: Vref ≤Vout ≤ (Vin - 1V), 2.3 ≤Vin≤30V, 100µA≤IL≤ 150 mA, TJ ≤ TJMAX.
Advanced Monolithic Systems, Inc. 6680B Sierra Lane, Dublin, CA 94568 Phone (925) 556-9090 Fax (925) 556-9140
AMS2950/AMS2951
Note 8: The junction-to-ambient thermal resistance are as follows:180°C/W and 160°C/W for the TO-92 (N) package with 0.40 inch and 0.25 inch leads to the
printed circuit board (PCB) respectively, 105°C/W for the molded plastic DIP (P) and 160°C/W for the molded plastic SO-8 (S). The above thermal resistances
for the N, S and P packages apply when the package is soldered directly to the PCB.
Note 9: May exceed input supply voltage.
Note 10: When used in dual-supply systems where the output terminal sees loads returned to a negative supply, the output voltage should be diode-clamped to
ground.
Note 11: Vshutdown ≥ 2V, Vin ≤ 30V, Vout =0, Feedback pin tied to 5VTAP.
Note 12: Output or reference voltage temperature coefficients defined as the worst case voltage change divided by the total temperature range.
Note 13: Thermal regulation is defined as the change in output voltage at a time T after a change in power dissipation is applied, excluding load or line
regulation effects. Specifications are for a 50mA load pulse at VIN =30V (1.25W pulse) for T =10 ms.
Note 14: 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 15: Line regulation for the AMS2951 is tested at 150°C for IL = 1 mA. For IL = 100 µA and TJ = 125°C, line regulation is guaranteed by design to 0.2%.
See typical performance characteristics for line regulation versus temperature and load current.
Note 16: All AMS2950 devices have the nominal output voltage coded as the last two digits of the part number. In the AMS2951 products, the 2.5V 3.0V and
3.3V versions are designated by the last two digits, but the 5V version is denoted with no code of the part number.
BLOCK DIAGRAM AND TYPICAL APPLICATIONS
AMS2950-XX AMS2951-XX
INPUT
OUTPUT
GROUND
ERROR
AMPLIFIER
1.23V
REFERENCE
UNREGULATED DC
VOUT
IL≤ 150mA
SEE APPLICATION
HINTS
+
+
+
+
-
INPUT OUTPUT
GROUND
ERROR
AMPLIFIER
1.23V
REFERENCE
UNREGULATED DC V
OUT
I
L
≤
150mA
SEE APPLICATION
HINTS
+
+
+
+
-
FEED-
BACK
SHUT-
DOWN
SENSE
V
TAP
ERROR TO CMOS
OR TTL
+
-
+
330k
Ω
4
5
6
2
187
3
FROM
CMOS
OR TTL
50mV
ERROR DETECTION COMPARATOR
Advanced Monolithic Systems, Inc. 6680B Sierra Lane, Dublin, CA 94568 Phone (925) 556-9090 Fax (925) 556-9140
AMS2950/AMS2951
TYPICAL PERFORMANCE CHARACTERISTICS
0
40
100
60
160
0 1 2 3 4 5 6 7 8
INPUT VOLTAGE (V)
Quiescent Current
QUIESCENT CURRENT (µA)
125
250
Input Current
25
50
75
100
150
175
200
225
INPUT VOLTAGE (V)
INPUT CURRENT (µA)
5V OUTPUT
-75 0 25 50 75 100 125
5.06
5.0
150
OUTPUT VOLTAGE (V)
Temperature Drift of 3
Representative Units
TEMPERATURE (° C)
5.04
4.98
4.94 -50 -25
0.1 1 10 150
LOAD CURRENT (mA)
GROUND CURRENT (mA)
0.01
0.1
1
10 Quiescent Current Dropout Characteristics
INPUT VOLTAGE (V)
OUTPUT VOLTAGE (V)
RL= 50 kΩ
0
90
270 Input Current
15
30
45
75
120
150
180
210
INPUT VOLTAGE (V)
INPUT CURRENT (mA)
-75 0 25 50 75 100 125
120
90
150
QUIESCENT CURRENT (µA)
Quiescent Current
TEMPERATURE (° C)
100
70
60
-50 -25
IL= 100µA
-75 0 25 50 75 100 125
10
150
QUIESCENT CURRENT (mA)
Quiescent Current
TEMPERATURE (° C)
9
8
7-50 -25
IL= 150mA
50
80
110
20
80
140
120
0
2
5
3
8
0 1 2 3 4 5 6 7 8
INPUT VOLTAGE (V)
Quiescent Current
QUIESCENT CURRENT (µA)
1
4
7
6
01 2 3 4 5 6 1 2 3 4 5 6 7 8 9 100
0
1
2
3
4
5
6
0
1 2 3 4 5 6 7 8 9 100
60
240
5.02
4.96
5V OUTPUT
5V OUTPUT5V OUTPUT 5V OUTPUT
5V OUTPUT
5V OUTPUT
5V OUTPUT
IL= 1 mA
IL= 150mA
RL= 50Ω
RL= 50 kΩ
IL= 0
VIN= 6V
VIN= 6V
RL= 50Ω
0.2%
RL= ∞
Advanced Monolithic Systems, Inc. 6680B Sierra Lane, Dublin, CA 94568 Phone (925) 556-9090 Fax (925) 556-9140
AMS2950/AMS2951
TYPICAL PERFORMANCE CHARACTERISTICS (Continued)
-75 0 25 50 75 100 125
170
140
150
SHORT CIRCUIT CURRENT (mA)
Short Circuit Current
TEMPERATURE (° C)
150
120
110
-50 -25 -75 0 25 50 75 100125
600
150
DROPOUT VOLTAGE (mV)
Dropout Voltage
TEMPERATURE (° C)
400
100
0-50 -25
IL= 150mA
100
130
160
-75 025 50 75 100125
2.2
150
MINIMUM OPERATING VOLTAGE (V)
AMS2951 Minimum Operating Voltage
TEMPERATURE (° C)
-50 -25 -75 0 25 50 75 100125
20
150
BIAS CURRENT (nA)
AMS2951 Feedback Bias Current
TEMPERATURE (° C)
0
-30 -50 -25 -2.0 -1.5 -1.0 -0.5 00.5
-250
50
-50
-150
AMS2951 Feedback Pin Current
1.0
FEEDBACK VOLTAGE (V)
FEEDBACK CURRENT (µA)
-200
0
-100
200 400 600
100
mV
800
INPUT
VOLTAGE
Line Transient Response
TIME (µs)
0
8V
4V 0
IL= 1mA
VOUT= 5V
0.0 0.3 0.4 0.5 0.6 0.7 0.8
2.5
0.9
SINK CURRENT (mA)
AMS2951 Comparator Sink Current
OUTPUT LOW VOLTAGE (V)
1.5
0.0 0.1 0.20 3 4 5 6 7 8
9
4
ERROR OUTPUT (V)
AMS2951 Error Comparator Output
INPUT VOLTAGE (V)
5
2
1
1 2
0
3
6
VOUT= 5V
100µA1mA 10mA 150mA
OUTPUT CURRENT
DROPOUT VOLTAGE (mV)
0
500 Dropout Voltage
500
300
50
400
300
200
100
2.1
2.0
1.9
1.8
1.7
1.6
10
-10
-20
50
mV
-50
mV
6V
OUTPUT VOLTAGE
CHANGE
~
~
~
~
8
72.0
1.0
0.5
IL= 100µA
TJ = 25°C
TA = 125°C
TA = 25°C
TA = -55°C
PIN 7 DRVEN BY EXTERNAL
SOURCE (REGULATOR RUN
OPEN LOOP)
TA = 125°C
TA = 25°C
TA = -55°C
CL= 1µF
HYSTERESIS
50k RESISTOR TO
EXTERNAL 5V SUPPLY
50k
RESISTOR
TO VOUT
Advanced Monolithic Systems, Inc. 6680B Sierra Lane, Dublin, CA 94568 Phone (925) 556-9090 Fax (925) 556-9140
AMS2950/AMS2951
TYPICAL PERFORMANCE CHARACTERISTICS (Continued)
Load Transient Response
TIME (ms)
OUTPUT VOLTAGE
CHANGE (mV)
CL= 1 µF
0 1 2 3 4 5
100
0
50
150
250
VOUT = 5V
2
7
AMS2951 Enable Transient
0
2
0
1
3
4
5
6
TIME (µs)
SHUTDOWN PIN
VOLTAGE (V)
0 100 200 300 400 500 600 700-100
-2
IL= 10 mA
200
100
-50
-100
150
mA
µA
~
~
~
~
LOAD
CURRENT
Load Transient Response
TIME (ms)
OUTPUT VOLTAGE
CHANGE (mV)
0 4 8 12 16 20
100
-20
0
40
80
60
20
-40
-60
150
mA
µA
~
~
LOAD
CURRENT
OUTPUT
VOLTAGE (V)
CL= 10 µF
VOUT = 5V
VOUT = 5V
CL= 10 µF
CL= 1 µF
VIN = 8V
10 100 1K 100K
FREQUENCY (Hz)
OUPUT IMPEDANCE (Ω)
0.01
10 Output Impedance
2
1
0.05
0.02
101104105
90
60
106
RIPPLE REJECTION (dB)
Ripple Rejection
FREQUENCY (Hz)
70
40
30
102
IL= 100µA
20
50
80
VIN= 6V
103101104105
90
60
106
RIPPLE REJECTION (dB)
Ripple Rejection
FREQUENCY (Hz)
70
40
30
102
IL= 1mA
20
50
80
VIN= 6V
103
101104105
80
50
106
RIPPLE REJECTION (dB)
Ripple Rejection
FREQUENCY (Hz)
60
30
20
102
IL= 50mA
10
40
70
VIN= 6V
103
FREQUENCY (Hz)
VOLTAGE NOISE SPECTRAL
DENSITY(mV/√Hz)
0.0
3.5 AMS2951 Output Noise
2.0
1.5
0.5
104105
102103
1.0
3.0
2.5
-75 0 25 50 75 100 125
400
200
150
PIN 2 TO PIN 4 RESISTANCE (kΩ)
AMS2951 Divider Resistance
TEMPERATURE (° C)
300
100
-50 -25
0
5
0.1
0.2
0.5
10K 1M
CL= 1 µF
IL= 150mA
CL= 220 µF
CL= 3.3 µF
0.01 µF
BYPASS
PIN 1 TO
PIN 7
5V OUTPUT
IL= 150mA
CL= 1µF
VOUT= 5V
CL= 1 µF
VOUT = 5V
IO= 1 mA
IO= 100µA
IO= 100mA
VOUT = 5V
CL= 1 µF
IL= 0 VOUT = 5V
CL= 1 µF
IL= 10mA
Advanced Monolithic Systems, Inc. 6680B Sierra Lane, Dublin, CA 94568 Phone (925) 556-9090 Fax (925) 556-9140
AMS2950/AMS2951
TYPICAL PERFORMANCE CHARACTERISTICS (Continued)
-75 0 25 50 75 100 125
1.8
1.2
150
SHUTDOWN TRESHOLD VOLTAGE (V)
Shutdown Treshold Voltage
TEMPERATURE (° C)
1.6
1.0
0.6 -50 -25
1.4
0.8
REGULATOR OFF
0 5 10 15 20 25
0
120
80
40
AMS2951 Maximum Rated
Output Current
30
INPUT VOLTAGE (V)
OUTPUT CURRENT (mA)
20
100
60
0
5
Thermal Response
0
1
-2
2
4
TIME (µs)
POWER
DISSIPATION (W)
10 20 30 40 500
-1
5 15 20 25
30
0
30
OUTPUT VOLTAGE CHANGE (V)
Line Regulation
INPUT VOLTAGE (V)
10
-10 10
IL= 100µA
10
-5
5
0
~
~
5
25
20
15
0 5 10 15 20 25
0
120
80
40
AMS2950 Maximum Rated
Output Current
30
INPUT VOLTAGE (V)
OUTPUT CURRENT (mA)
20
100
60
~
~
OUTPUT VOLTAGE
CHANGE (mV)
1.25W
TA= 25° C
TA= 50° C
TA= 25° C
TA= 85° C
TA= 85° C
TJMAX= 125° C
VOUT = 5V
8 PIN MOLDED
DIP SOLDERED
TO PC BOARD
REGULATOR ON
TO-92 PACKAGE
.25"LEADS SOLDERED
TO PC BOARD
TJMAX= 125° C
IL= 1mA
IL= 100µA
TJ = 150° C
TJ = 125° C
Advanced Monolithic Systems, Inc. 6680B Sierra Lane, Dublin, CA 94568 Phone (925) 556-9090 Fax (925) 556-9140
AMS2950/AMS2951
APPLICATION HINTS
External Capacitors
A 1.0
µ
F or greater capacitor is required between output and
ground for stability at output voltages of 5V or more. At lower
output voltages, more capacitance is required (2.2
µ
or more is
recommended for 3V and 3.3V versions). Without this capacitor
the part will oscillate. Most types of tantalum or aluminum
electrolytic works fine here; even film types work but are not
recommended for reasons of cost. Many aluminum types have
electrolytes that freeze at about -30
°
C, so solid tantalums are
recommended for operation below -25
°
C. The important
parameters of the capacitor are an ESR of about 5
Ω
or less and
resonant frequency above 500 kHz parameters in the value of the
capacitor. The value of this capacitor may be increased without
limit.
At lower values of output current, less output capacitance is
required for stability. The capacitor can be reduced to 0.33
µ
F for
currents below 10 mA or 0.1
µ
F for currents below 1 mA. Using
the adjustable versions at voltages below 5V runs the error
amplifier at lower gains so that more output capacitance is needed.
For the worst-case situation of a 200mA load at 1.23V output
(Output shorted to Feedback) a 3.3µF (or greater) capacitor should
be used.
Unlike many other regulators, the AMS2950, will remain stable
and in regulation with no load in addition to the internal voltage
divider. This is especially important in CMOS RAM keep-alive
applications. When setting the output voltage of the AMS2951
version with external resistors, a minimum load of 1
µ
A is
recommended.
A 1
µ
F tantalum or aluminum electrolytic capacitor should be
placed from the AMS2950/AMS2951 input to the ground 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.
Stray capacitance to the AMS2951 Feedback terminal can cause
instability. This may especially be a problem when using a higher
value of external resistors to set the output voltage. Adding a 100
pF capacitor between Output and Feedback and increasing the
output capacitor to at least 3.3 µF will fix this problem.
Error Detection Comparator Output
The comparator produces a logic low output whenever the
AMS2951 output falls out of regulation by more than
approximately 5%. This figure is the comparator’s built-in offset
of about 60 mV divided by the 1.235 reference voltage (Refer to
the block diagram). This trip level remains “5% below normal”
regardless of the programmed output voltage of the 2951. For
example, the error flag trip level is typically 4.75V for a 5V output
or 11.4V for a 12V output. The out of regulation condition may be
due either to low input voltage, current limiting, or thermal
limiting.
Figure 1 gives a timing diagram depicting the ERROR signal and
the regulator output voltage as the AMS2951 input is ramped up
and down. For 5V versions the ERROR signal becomes valid
(low) at about 1.3V input. It goes high at about 5V input (the input
voltage at which Vout = 4.75 ).
Since the AMS2951’s dropout voltage is load dependent (see
curve in typical performance characteristics), the input voltage trip
point (about 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. This resistor may be returned to the
output or some other supply voltage depending on system
requirements. In determining a value for this resistor, note that the
output is rated to sink 400
A, this sink current adds to battery
drain in a low battery condition. Suggested values range from
100K to 1MΩ. The resistor is not required if this output is unused.
Programming the Output Voltage (AMS2951)
The AMS2951 may be pin-strapped for the nominal fixed output
voltage using its internal voltage divider by tying the output and
sense pins together, and also tying the feedback and V
pins
together. Alternatively, 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.
The complete equation for the output voltage is:
Vout = VREF × (1 + R1/ R2)+ IFBR1
where V
is the nominal 1.235 reference voltage and I
is the
feedback pin bias current, nominally -20 nA. The minimum
recommended load current of 1
A forces an upper limit of 1.2
M
on value of R
, if the regulator must work with no load (a
condition often found in CMOS in standby) I
will produce a 2%
typical error in V
which may be eliminated at room
temperature by trimming R
. For better accuracy, choosing R2 =
100k reduces this error to 0.17% while increasing the resistor
program current by 12 µA. Since the AMS2951 typically draws 60
A at no load with Pin 2 open-circuited, this is a small price to
pay.
Reducing Output Noise
In reference applications it may be an advantageous to reduce the
AC noise present at the output. One method 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
AMS2950 but is relatively inefficient, as increasing the capacitor
from 1
F to 220
F only decreases the noise from 430
V to 160
µV rms for a 100 kHz 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 about 0.01
F. When doing this, the output capacitor must be
increased to 3.3
F to maintain stability. These changes reduce
the output noise from 430
V to 100
V rms for a 100 kHz
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.
Advanced Monolithic Systems, Inc. 6680B Sierra Lane, Dublin, CA 94568 Phone (925) 556-9090 Fax (925) 556-9140
AMS2950/AMS2951
APPLICATION HINTS (Continued)
OUTPUT
VOLTAGE
ERROR*
INPUT
VOLTAGE
4.75V
5V
1.3V
R1
ERROR*
ERROR
OUPUT
**SHUTDOWN
INPUT
GND FB
VOUT
VREF R2
SD
1.23V
74
3
8
15 +VIN
+VIN
VOUT
1.2 30V
3.3µF
.01
µF
+*
100k
AMS2951
FIGURE 1. ERROR Output Timing FIGURE 2. Adjustable Regulator
*When
V
IN
1.3V the error flag pin becomes a high impedance,
and the error flag voltage rises to its pull-up voltage. Using V
out
as the pull-up voltage (see Figure 2), rather than an external 5V
source, will keep the error flag voltage under 1.2V (typ.) in this
condition. The user may wish to drive down the error flag voltage
using equal value resistors (10 k suggested), to ensure a low-
level logic signal during any fault condition, while still allowing
a valid high logic level during normal operation.
*See Application Hints.
Vout = VREF × (1 + R1/ R2)
**Drive with TTL- high to shut down. Ground or leave if shutdown
feature is not used.
Note: Pins 2 and 6 are left open.
TYPICAL APPLICATIONS
300 mA Regulator with 0.75 Dropout Wide Input Voltage Range Current Limiter
UNREGULATED
INPUT
LOAD
50mA TO
300mA
GNDFB
OUTIN
47
62
18
VTAP
AMS2951
2N5432 (2)
SENSE 5V OUTPUT
4.7µF
27kΩ
330Ω
ERROR
ERROR
OUPUT
SHUTDOWN
INPUT
GND FB
VOUT
SD
74
3
8
15 +VIN
+VIN
AMS2951
*VOUT ≈ VΙΝ
*Minimum Input-Output voltage ranges from 40mV to 400mV, depending on
load current. Current limit is typically 160 mA
Advanced Monolithic Systems, Inc. 6680B Sierra Lane, Dublin, CA 94568 Phone (925) 556-9090 Fax (925) 556-9140
AMS2950/AMS2951
TYPICAL APPLICATIONS (Continued)
Low Drift Current Source 5Volt Current Limiter
SHUTDOWN
INPUT
GND FB
VOUT
SD
74
3
8
1
VIN
+V = 2
AMS2951
LOAD
30V
IL
R
1% 1µF
0.1µF
+
GND
VOUT
+VIN
5V BUS
AMS2950 -5.0 *VOUT ≈ 5V
1µF
*Minimum Input-Output voltage ranges from 40mV to 400mV, depending on
load current. Current limit is typically 160 mA
5V Regulator with 2.5V Sleep Function Open Circuit Detector for 4 to 20mA Current Loop
ERROR
ERROR
OUPUT
SHUTDOWN
INPUT
GND FB
VOUT
SD
74
3
8
15 +VIN
+VIN
AMS2951
C - MOS
GATE
200kΩ
100kΩ
100kΩ
3.3µF
470kΩ
47kΩ
*SLEEP
INPUT
1%
1%
100pF
2N3906
+VOUT
+GND
VOUT
+VIN
+5V
AMS2951
*OUTPUT
0.1µF
FB
4.7kΩ
360
1N4001
1N457
4
8
1
4
MIN. VOLTAGE ≈ 4V
20mA
72
15
4
Advanced Monolithic Systems, Inc. 6680B Sierra Lane, Dublin, CA 94568 Phone (925) 556-9090 Fax (925) 556-9140
AMS2950/AMS2951
TYPICAL APPLICATIONS (Continued)
2 Ampere Low Dropout Regulator Regulator with Early Warning and Auxiliary Output
ERROR ERROR
FLAG
CURRENT
LIMIT SECTION
GND
FB
VOUT
SD
14
3
8
5
7
+VIN
+VIN = VOUT +.5V
AMS2951
+VOUT @ 2A
R1
R2
10kΩ
100µF
4.7
TANT.
++
1%
220
.033
20kΩ
4.7MΩ
2N3906
0.05
680
470
MJE2955
ERROR
GND
FB
VOUT
5
4
8
1
6
+VIN
AMS2951
#1
VTAP
7
ERROR
GND
FB
VOUT
4
8
6+VIN
AMS2951
#2
VTAP
3SD
7
SENSE
2
5
RESET
1µF
20
+VIN D1
D2
3.6V
NICAD
27 kΩ
2.7MΩ
330 kΩ
1µF
D4
Q1
MAIN 5V OUTPUT µP
VDD
2
D3
5V MEMORY
SUPPLY
EARLY WARNING
SENSE
+
+
VOUT = 1.23V(1+R1/R2)
For 5V VOUT, use internal resistors. Wire pin 6 to 7 and pin 2 to +VOUTBuss.
• Early warning flag on low input voltage
• Main output latches off at lower input voltages
• Battery backup on auxiliary output
Operation: Reg.#1’s VOUT is programmed one diode drop above 5V. It’s error flag
becomes active when VIN≤ 5.7V. When VIN drops below 5.3V, the error flag of
Reg.#2 becomes active and via Q1 latches the main output off. When VIN again
exceeds 5.7V Reg.#1 is back in regulation and the early warning signal rises,
unlatching Reg.#2 via D3.
1A Regulator with 1.2V Dropout Latch Off When Error Flag Occurs
OUTPUT
5V ± 1% @
0 TO 1A
GND
FB OUT
IN
4
7
6
1
2
8
VTAP
AMS2951
SUPERTEX
VP12C
SENSE
0.002µ
F
2
k
Ω
10
k
Ω
1ΜΩ
0.01µ
F
220µ
F
1µ
F
+
IQ
≅
400
µ
A
UNREGULATED
INPUT
R1
ERROR
GND FB
VOUT
R2
SD 7
4
3
8
15 +VIN
+VIN
VOUT
1µF
+
470kΩ
AMS2951
470kΩ
RESET
Advanced Monolithic Systems, Inc. 6680B Sierra Lane, Dublin, CA 94568 Phone (925) 556-9090 Fax (925) 556-9140
AMS2950/AMS2951
PACKAGE DIMENSIONS inches (millimeters) unless otherwise noted.
3 LEAD TO-92 PLASTIC PACKAGE (N)
8 LEAD SOIC PLASTIC PACKAGE (S)
0.140±0.010
(3.556±0.127)
0.060±0.010
(1.524±0.254)
0.015±0.002
(0.381±0.051)
0.016±0.003
(0.406±0.076)
0.050±0.005
(1.270±0.127)
0.060±0.005
(1.524±0.127)
DIA
0.180±0.005
(4.572±0.127)
0.180±0.005
(4.572±0.127)
0.050
(1.270)
MAX
0.500
(12.70)
MIN UNCONTROLLED
LEAD DIMENSIONS
10°
NOM
5° NOM
N (TO-92 ) AMS DRW# 042391
0.90
(2.286)
NOM
0°-8° TYP
0.010-0.020
(0.254-0.508)
S (SO-8 ) AMS DRW# 042293
x 45°
0.016-0.050
(0.406-1.270)
0.008-0.010
(0.203-0.254)
0.004-0.010
(0.101-0.254)
0.014-0.019
(0.355-0.483)
0.053-0.069
(1.346-1.752)
0.050
(1.270)
TYP
0.150-0.157**
(3.810-3.988)
0.228-0.244
(5.791-6.197)
0.189-0.197*
(4.801-5.004)
*DIMENSION DOES NOT INCLUDE MOLD FLASH. MOLD FLASH
SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE
**DIMENSION DOES NOT INCLUDE INTERLEAD FLASH. INTERLEAD
FLASH SHALL NOT EXCEED 0.010" (0.254mm) PER SIDE
1 2 3 4
8 7 6 5
Advanced Monolithic Systems, Inc. 6680B Sierra Lane, Dublin, CA 94568 Phone (925) 556-9090 Fax (925) 556-9140
AMS2950/AMS2951
PACKAGE DIMENSIONS inches (millimeters) unless otherwise noted (Continued).
8 LEAD PLASTIC DIP PACKAGE (P)
0.045-0.065
(1.143-1.651)
0.255±0.015*
(6.477±0.381)
0.400*
(10.160)
MAX
1 2 3 4
8 7 6 5
0.130±0.005
(3.302±0.127)
0.018±0.003
(0.457±0.076)
0.100±0.010
(2.540±0.254) (8.255 )
+0.635
-0.381
0.325 +0.025
-0.015
0.009-0.015
(0.229-0.381)
0.300-0.325
(7.620-8.255)
0.065
(1.651)
TYP
0.005
(0.127)
MIN
0.125
(3.175)
MIN 0.015
(0.380)
MIN
*DIMENSIONS DO NOT INCLUDE MOLD FLASH OR PROTUSIONS.
MOLD FLASH OR PROTUSIONS SHALL NOT EXCEED 0.010" (0.254mm)
P (8L PDIP ) AMS DRW# 042294