AMS AMS2942

AMS2942
FEATURES
APPLICATIONS
• Adjustable from 1.23V to 42V
• High Accuracy Output Voltage
• Extremely Low Quiescent Current
• Low Dropout Voltage
• Tight Load and Line Regulation
• Low Temperature Coefficient
• Current and Thermal Protection
• Unregulated DC Positive Transients 60V
• Error Flag Warning of Voltage Output Dropout
• Logic Controlled Electronic Shutdown
• Telephone Systems
• High Voltage Power Supply
• Cordless Telephones
• Laboratory Instrumentation
• Radio Control Systems
• Automotive Electronics
• Avionics
GENERAL DESCRIPTION
The AMS2942 are micropower voltage regulators ideally suited for use with high voltage powered systems. This device
feature very low quiescent current (typ.130µA), and very low dropout voltage (typ.45mV at light loads and 380mV at
100mA). The quiescent current increases only slightly in dropout. The AMS2942 has positive transient protection up to 60V
and can survive unregulated input transient up to 20V below ground.
AMS2942 is designed with a tight initial voltage reference tolerance, 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 regulator in telephone
applications, using the telephone line as a power source.
The AMS2942 is available in a special 8-pin plastic SOIC in which pin 2 and 3 are fused together with the package paddle
serving also as heat sink. An error flag output warns of a low output voltage, often due to failing voltage on input line. A
logic-compatible shutdown input is available, which enables the regulator to be switched on and off. The output voltage can be
programmed from 1.23V to 42V with an external pair of resistors.
ORDERING INFORMATION
PACKAGE TYPE
8 LEAD SOIC
AMS2942AS
AMS2942BS
PIN CONNECTION
8L SOIC
OPERATING
TEMP. RANGE
IND
IND
OUTPUT 1
8 INPUT
GROUND 2
7 FEEDBACK
GROUND 3
6 N/C
ON/OFF 4
5 ERROR
Top View
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AMS2942
ABSOLUTE MAXIMUM RATINGS (Note 1)
Input Supply Voltage
Power Dissipation
Junction Temperature
Storage Temperature
Soldering (25 Sec.)
-0.3 to +50V
Internally Limited
+150°C
-65°C to +150°C
265°C
ESD
2000V
OPERATING RATINGS (Note 1)
Max. Input Supply Voltage
Junction Temperature Range
(TJ) (Note 8)
45V
-40°C to +125°C
ELECTRICAL CHARACTERISTICS at VS=VOUT+1V, TA=25°C, unless otherwise specified.
Parameter
Conditions
AMS2942A
(Note 2)
Min.
Reference Voltage
1.22
Typ.
1.235
AMS2942B
Max.
Min.
1.25
1.21
1.27
1.185
Typ.
1.235
Units
Max.
1.26
V
1.285
V
Reference Voltage
Over Temperature (Note 7)
Output Voltage
Temperature Coefficient
(Note 10) (Note 4)
Line Regulation (Note 12)
6V ≤ V ≤ 45V (Note 13)
0.05
0.2
0.1
0.4
%
Load Regulation (Note 12)
100 µA ≤I ≤ 100 mA
0.05
0.2
0.1
0.4
%
Dropout Voltage
(Note 5)
I = 100µ A
50
80
50
80
mV
I = 100 mA
380
450
380
450
mV
I = 100 µA
120
180
120
180
µA
Ground Current
1.19
20
IN
L
L
L
L
I = 100 mA
ppm/°C
50
8
12
8
12
mA
160
200
160
200
mA
(Note 11)
0.05
0.2
0.05
0.2
%/W
Output Noise,
C = 1µF
L
430
430
µV rms
10Hz to 100KHz
C = 200 µF
L
160
160
C = 13.3 µF
µV rms
L
100
100
µV rms
L
Current Limit
V
Thermal Regulation
OUT
=0
(Bypass = 0.01 µF pins 7 to 1)
Feedback Pin Bias Current
40
Reference Voltage Temperature
Coefficient
Feedback Pin Bias Current
Temperature Coefficient
Error Comparator
( Note 10)
Output Leakage Current
V
Output Low Voltage
V = 4.5V, I
Upper Threshold Voltage
(Note 6)
Lower Threshold Voltage
(Note 6)
75
Hysteresis
(Note 6)
15
80
40
20
0.1
OH
= 42V
IN
OL
= 400µA
40
80
50
nA
ppm/°C
0.1
nA/°C
0.05
2
0.05
2
µA
150
250
150
250
mV
60
40
95
60
75
mV
95
15
mV
mV
Shutdown Input
Input logic Voltage
1.3
Low (Regulator ON)
0.7
2.5
High (Regulator OFF)
1.3
0.7
V
µA
2.5
V
Shutdown Pin Input Current
(Note 3)
VS = 2.5V
V = 42V
30
60
30
60
600
850
600
850
µA
Regulator Output Current in
Shutdown (Note 3)
(Note 9)
15
50
15
50
µA
S
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AMS2942
BLOCK DIAGRAM AND TYPICAL APPLICATIONS
AMS2942
39V to 45V UNREGULATED DC
VO = 38V
+
INPUT
FROM
CMOS
OR TTL
OUTPUT
+
SHUTDOWN
10µF
330kΩ
+
-
+
50mV
+
ERROR
AMPLIFIER
298kΩ
FEEDBACK
10kΩ
+
ERROR
1.23V
REFERENCE
TO CMOS
OR TTL
GROUND
ERROR DETECTION COMPARATOR
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. 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, 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≤42V, 100µA≤IL≤ 100 mA, TJ ≤ TJMAX.
Note 8: The junction-to-ambient thermal resistance is 120°C/W for the molded plastic SO-8 (S), when the package is soldered directly to the PCB.
Note 9: VSHUTDOWN ≥ 2.5V, VIN ≤ 42V, VOUT =0.
Note 10: Output or reference voltage temperature coefficients defined as the worst case voltage change divided by the total temperature range.
Note 11: 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 =42V (1.25W pulse) for T =10 ms.
Note 12: 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 13: Line regulation 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.
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AMS2942
TYPICAL PERFORMANCE CHARACTERISTICS
Quiescent Current
10
0.1
1
10
LOAD CURRENT (mA)
140
120
IL= 1 mA
100
80
IL= 0
60
40
20
0
100
0
Short Circuit Current
1
2 3
4
5 6
INPUT VOLTAGE (V)
7
9
VIN= VOUT+1V
IL= 100mA
8
7
-75 -50 -25 0 25 50 75 100 125 150
TEMPERATURE (° C)
8
Dropout Voltage
Dropout Voltage
600
DROPOUT VOLTAGE (mV)
160
150
140
130
120
110
500
500
400
IL= 100mA
300
~
~
100
50
IL= 100µA
DROPOUT VOLTAGE (mV)
170
0
-75 -50 -25 0 25 50 75 100 125 150
TEMPERATURE (° C)
100
-75 -50 -25 0 25 50 75 100 125 150
TEMPERATURE (° C)
Minimum Operating Voltage
2.1
BIAS CURRENT (nA)
1.8
1.7
200
TJ = 25°C
100
0
-10
-20
1mA
10mA
OUTPUT CURRENT
100mA
Feedback Pin Current
50
10
1.9
300
Feedback Bias Current
20
2.2
2.0
400
0
100µA
FEEDBACK CURRENT ( µA)
SHORT CIRCUIT CURRENT ( mA)
QUIESCENT CURRENT (mA)
QUIESCENT CURRENT ( µA)
GROUND CURRENT (mA)
1
0.01
0.1
MINIMUM OPERATING VOLTAGE (V)
Quiescent Current
Quiescent Current
160
10
0
PIN 7 DRVEN BY EXTERNAL
SOURCE (REGULATOR RUN
OPEN LOOP)
-50
TA = 125°C
-100
-150
TA = 25°C
-200
TA = -55°C
1.6
-75 -50 -25 0 25 50 75 100 125 150
TEMPERATURE (° C)
-30
-75 -50 -25 0 25 50 75 100 125 150
TEMPERATURE (° C)
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-250
-2.0
0
0.5
-1.5 -1.0 -0.5
FEEDBACK VOLTAGE (V)
1.0
AMS2942
TYPICAL PERFORMANCE CHARACTERISTICS (Continued)
100
mA
100
µA
1
2
3
TIME (ms)
4
5
0
RIPPLE REJECTION (dB)
IO= 100mA
IO= 1 mA
0.5
0.2
VOUT = 5V
CL= 1 µF
0.05
0.02
0.01
16
20
CL= 1 µF
5
4
IL= 10 mA
VIN = 8V
3
2
1
0
2
CL= 10 µF
~
~
0
-2
-100 0 100 200 300 400 500 600 700
TIME (µs)
Ripple Rejection
90
90
80
80
70
IL= 0
60
50
40
CL= 1 µF
VIN= 6V
30
IL= 100µA
VOUT = 5V
70
CL= 1 µF
VIN= VOUT+1V
IL= 1mA
60
50
40
30
IL= 10mA
10
100
1K
10K 100K
FREQUENCY (Hz)
20
10 1
1M
Error Comparator Output
10 2
10 5
10 3
10 4
FREQUENCY (Hz)
20
10 1
10 6
Error Comparator Sink Current
9
2.5
7
50k RESISTOR TO
EXTERNAL 5V SUPPLY
6
5
4
HYSTERESIS
3
50k
RESISTOR
TO VOUT
2
1
0
0
1
2 3 4 5 6 7
INPUT VOLTAGE (V)
8
SINK CURRENT (mA)
VOUT= 5V
8
ERROR OUTPUT (V)
8
12
TIME (ms)
TA = 125°C
2.0
1.5
TA = 25°C
1.0
TA = -55°C
0.5
INPUT OUTPUT VOLTAGE
VOLTAGE
CHANGE
OUPUT IMPEDANCE (Ω)
2
0.1
4
7
6
Ripple Rejection
IO= 100µA
1
OUTPUT
VOLTAGE (V)
~
~
Output Impedance
10
5
CL= 10 µF
RIPPLE REJECTION (dB)
0
100
mA
100
µA
Enable Transient
SHUTDOWN PIN
VOLTAGE (V)
CL= 1 µF
~
~
OUTPUT VOLTAGE
CHANGE (mV)
Load Transient Response
80
60
40
20
0
-20
-40
-60
LOAD
CURRENT
LOAD
CURRENT
OUTPUT VOLTAGE
CHANGE (mV)
Load Transient Response
250
200
150
100
50
0
-50
-100
0.0
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9
OUTPUT LOW VOLTAGE (V)
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10 2
10 5
10 3
10 4
FREQUENCY (Hz)
10 6
Line Transient Response
100
mV
50
mV
0
-50
mV
CL= 1µF
IL= 1mA
~
~
VOUT= 5V
8V
6V
4V
0
200
400
TIME (µs)
600
800
AMS2942
APPLICATION HINTS
External Capacitors
Setting the Output Voltage
A 1.0 µF 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. 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 µF for
currents below 10 mA or 0.1 µF for currents below 1 mA. At
voltages below 5V the error amplifier operates at lower gains so
that more output capacitance is needed. For the worst-case
situation of a 100mA load at 1.23V output (Output shorted to
Feedback) a 3.3µF (or greater) capacitor should be used.
A 1µF tantalum or aluminum electrolytic capacitor should be
placed between input to 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 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.
The AMS2942 it may be programmed for any output voltage
between its 1.235V reference and its 42V 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 VREF is the nominal 1.235 reference voltage and IFB is the
feedback pin bias current, nominally -20 nA. The minimum
recommended load current of 1 µA forces an upper limit of 1.2
MΩ on value of R2, if the regulator must work with no load (a
condition often found in CMOS in standby) IFB will produce a 2%
typical error in VOUT which may be eliminated at room
temperature by trimming R1. For better accuracy, choosing R2 =
100k reduces this error to 0.17%.
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.
Noise could 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 µF. When doing this, the output capacitor must be
increased to 3.3 µF to maintain stability. These changes reduce
the output noise from 430 µV to 100 µV 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.
Error Detection Comparator Output
The comparator produces a logic low output whenever the 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. This trip level remains “5% below
normal” regardless of the programmed output voltage. 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 AMS2942 input is ramped up
and down.
Since the dropout voltage is load dependent the input voltage trip
point will vary with the load current. The output voltage trip point
does not vary with load. The error comparator has an opencollector output which requires an external pullup 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 400µA.
Suggested values range from 100K to 1MΩ. The resistor is not
required if error flag terminal is unused.
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AMS2942
APPLICATION HINTS (Continued)
+VIN
OUTPUT
VOLTAGE
4.75V
8
100k
VOUT
1.2
30V
+VIN
ERROR
OUPUT
ERROR*
**SHUTDOWN
INPUT
5V
INPUT
VOLTAGE
5 ERROR*
4
AMS2942
SD
R1
GND
3
1.3V
1
VOUT
2
FB
7
*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.
PACKAGE DIMENSIONS inches (millimeters) unless otherwise noted.
8 LEAD SOIC PLASTIC PACKAGE (S)
0.189-0.197*
(4.801-5.004)
7
6
5
0.228-0.244
(5.791-6.197)
0.150-0.157**
(3.810-3.988)
1
2
3
4
0.010-0.020 x 45°
(0.254-0.508)
0.053-0.069
(1.346-1.752)
0.004-0.010
(0.101-0.254)
0.014-0.019
(0.355-0.483)
R2
FIGURE 2. Adjustable Regulator
*When VIN ≤1.3V the error flag pin becomes a high impedance,
and the error flag voltage rises to its pull-up voltage. Using Vout
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 kΩ suggested), to ensure a
low-level logic signal during any fault condition, while still
allowing a valid high logic level during normal operation.
8
3.3µF
1.23
V
VREF
FIGURE 1. ERROR Output Timing
* +
.01µ
F
0.008-0.010
(0.203-0.254)
0.050
(1.270)
TYP
0°-8° TYP
0.016-0.050
(0.406-1.270)
*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
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S (SO-8 ) AMS DRW# 042293