The AMS1503 series of adjustable and fixed low dropout voltage regulators are designed to provide 3A output current to
power the new generation of microprocessors. The dropout voltage of the device is 100mV at light loads and rising to 500mV
at maximum output current. A second low current input voltage 1V or greater then the output voltage is required to achieve
this dropout. The AMS1503 can also be used as a single supply device.
New features have been added to the AMS1503: a remote Sense pin is brought out virtually eliminating output voltage
variations due to load changes. The typical load regulation, measured at the Sense pin, for a load current step of 100mA to 3A
is less than 1mV.
The AMS1503 series has fast transient response. The Adjust pin is brought out on fixed devices. To further improve the
transient response the addition of a small capacitor on the Adjust pin is recommended.
The AMS1503 series are ideal for generating power supplies of 2V to 3V where both 5V and 3.3V supplies are available.
The AMS1503 devices are offered in 5 lead TO-220, 5L TO-263 (plastic DD) and 5L TO-252 (DPAK) packages.
ORDERING INFORMATION:
OPERATING JUNCTION
5 LEAD TO-263 5 LEAD TO-220 5 LEAD TO-252
TEMPERATURE RANGE
AMS1503CM
AMS1503CT
AMS1503CD
0 to 125° C
AMS1503CM-1.5 AMS1503CT-1.5 AMS1503CD-1.5
0 to 125° C
AMS1503CM-2.5 AMS1503CT-2.5 AMS1503CD-2.5
0 to 125° C
AMS1503CM-2.85 AMS1503CT-2.85 AMS1503CD-2.85
0 to 125° C
AMS1503CM-3.0 AMS1503CT-3.0 AMS1503CD-3.0
0 to 125° C
AMS1503CM-3.3 AMS1503CT-3.3 AMS1503CD-3.3
0 to 125° C
AMS1503CM-3.5 AMS1503CT-3.5 AMS1503CD-3.5
0 to 125° C
AMS1503CM-5.0 AMS1503CT-5.0 AMS1503CD-5.0
0 to 125° C
PACKAGE TYPE
PIN CONNECTIONS
5 LEAD TO-220
5
4
3
2
1
V
POWER
V
CONTROL
OUTPUT
ADJUST/GND
SENSE
FRONT VIEW
5 LEAD TO-252
5
4
3
2
1
Vpower
Vcontrol
OUTPUT
ADJUST/GND
SENSE
FRONT VIEW
5 LEAD TO-263
5
4
3
2
1
Vpower
Vcontrol
OUTPUT
ADJUST/GND
SENSE
FRONT VIEW
Advanced Monolithic Systems, Inc.
www.advanced-monolithic.com
Phone (925) 443-0722
Fax (925) 443-0723
AMS1503
ABSOLUTE MAXIMUM RATINGS
(Note 1)
V
POWER
Input Voltage
V
CONTROL
Input Voltage
Operating Junction Temperature
Control Section
Power Transistor
Storage temperature
Soldering information
Lead Temperature (25 sec)
6V
13V
0°C to 125°C
0°C to 150°C
- 65°C to +150°C
Thermal Resistance
TO-220 package
TO-252 package
TO-263 package
*Minimum pad size is 0.038in
2
ϕ
JA
= 50°C/W
ϕ
JA
= 92°C/W*
ϕ
JA
= 30°C/W**
** With package soldering to 0.5in
2
copper area over backside
ground plane or internal power plane
ϕ
JA
can vary from 20°C/W to
>40°C/W
depending on mounting technique.
265°C
ELECTRICAL CHARACTERISTICS
Electrical Characteristics at I
LOAD
= 0 mA, and T
J
= +25°C unless otherwise specified.
Parameter
Reference Voltage
Device
AMS1503
Conditions
V
CONTROL
= 2.75V, V
POWER
=2V, I
LOAD
= 10mA
V
CONTROL
= 2.7V to 12V, V
POWER
=3.3V to 5.5V,
I
LOAD
= 10mA to 3A
V
CONTROL
= 4V, V
POWER
=2.V, I
LOAD
= 0mA
V
CONTROL
= 3V, V
POWER
=2.3V, I
LOAD
= 0mA to 3A
V
CONTROL
= 5V, V
POWER
=3.3V, I
LOAD
= 0mA
V
CONTROL
= 4V, V
POWER
=3.3V, I
LOAD
= 0mA to 3A
V
CONTROL
= 5.35V, V
POWER
=3.35V, I
LOAD
= 0mA
V
CONTROL
= 4.4V, V
POWER
=3.7V, I
LOAD
= 0mA to 3A
V
CONTROL
= 5.5V, V
POWER
=3.5V, I
LOAD
= 0mA
V
CONTROL
= 4.5V, V
POWER
=3.8V, I
LOAD
= 0mA to 3A
V
CONTROL
= 5.8V, V
POWER
=3.8V, I
LOAD
= 0mA
V
CONTROL
= 4.8V, V
POWER
=4.1V, I
LOAD
= 0mA to 3A
V
CONTROL
= 6V, V
POWER
=4V, I
LOAD
= 0mA
V
CONTROL
= 5V, V
POWER
=4.3V, I
LOAD
= 0mA to 3A
V
CONTROL
= 7.5V, V
POWER
=5.5V, I
LOAD
= 0mA
V
CONTROL
= 6.5V, V
POWER
=5.8V, I
LOAD
= 0mA to 3A
I
LOAD
= 10 mA , 1.5V≤ (V
CONTROL
- V
OUT
)
≤
12V
0.8V≤ (V
POWER
- V
OUT
)
≤
5.5V
V
CONTROL
= V
OUT
+ 2.5V, V
POWER
=V
OUT
+ 0.8V,
I
LOAD
= 10mA to 3A
V
CONTROL
= 5V, V
POWER
=3.3V, V
ADJ
= 0V (Note 3)
V
CONTROL
= V
OUT
+ 2.5V, V
POWER
=V
OUT
+ 0.8V,
I
LOAD
= 10mA to 3A
V
CONTROL
= V
OUT
+ 2.5V, V
POWER
=V
OUT
+ 0.8V,
I
LOAD
= 10mA to 3A
V
CONTROL
= 2.75V, V
POWER
= 2.05V, I
LOAD
= 10mA
(V
IN
- V
OUT
) = 5V
Min
1.243
1.237
1.491
1.485
2.485
2.475
2.821
2.833
2.982
2.970
3.280
3.235
3.479
3.430
4.930
4.950
Typ
1.250
1.250
1.500
1.500
2.500
2.500
2.850
2.850
3.000
3.000
3.300
3.300
3.500
3.500
5.000
5.000
1
Max
1.257
1.263
1.509
1.515
2.515
2.525
2.879
2.867
3.018
3.030
3.320
3.333
3.521
3.535
5.030
5.050
3
Units
V
V
V
V
V
V
V
V
V
V
V
V
V
V
V
V
mV
Output Voltage
AMS1503-1.5
AMS1503-2.5
AMS1503-2.85
AMS1503-3.0
AMS1503-3.3
AMS1503-3.5
AMS1503-5.0
Line Regulation
AMS1503/-1.5/-2.5/
-2.85/-3.0/-3.3/-3.5/-5.0
Load Regulation
AMS1503/-1.5/-2.5/
-2.85/-3.0/-3.3/-3.5/-5.0
Minimum Load
Current
Control Pin Current
(Note 4)
Ground Pin Current
(Note 4)
Adjust Pin Current
Current Limit
AMS1503
AMS1503/-1.5/-2.5/
-2.85/-3.0/-3.3/-3.5/-5.0
AMS1503-1.5/-2.5/-2.85/
-3.0/-3.3/-3.5/-5.0
AMS1503
AMS1503/-1.5/-2.5/
-2.85/-3.0/-3.3/-3.5/-5.0
Ripple Rejection
AMS1503/-1.5/-2.5/
-2.85/-3.0/-3.3/-3.5/-5.0
Thermal Regulation
Thermal Resistance
Junction-to-Case
AMS1503
1
5
mA
5
6
60
10
120
mA
mA
6
10
mA
5
3.0
3.5
120
4.0
µA
A
V
CONTROL
= V
POWER
= V
OUT
+ 2.5V, V
RIPPLE
= 1V
P-P
I
LOAD
= 1.5A
T
A
= 25°C, 30ms pulse
T Package: Control Circuitry/ Power Transistor
M & D Package: Control Circuitry/ Power Transistor
60
80
dB
0.002
0.020
0.65/2.70
0.65/2.70
%W
°C/W
°C/W
Advanced Monolithic Systems, Inc.
www.advanced-monolithic.com
Phone (925) 443-0722
Fax (925) 443-0723
AMS1503
ELECTRICAL CHARACTERISTICS
Electrical Characteristics at I
OUT
= 0 mA, and T
J
= +25°C unless otherwise specified.
Parameter
Dropout Voltage
Control Dropout
(V
CONTROL
- V
OUT
)
Power Dropout
(V
POWER
- V
OUT
)
AMS1503/-1.5/-2.5/-
2.85/-3.0/-3.3/-3.5/-5.0
AMS1503/-1.5/-2.5/-
2.85/-3.0/-3.3/-3.5/-5.0
Device
Conditions
Note 2
V
POWER
=V
OUT
+ 0.8V, I
LOAD
= 10mA
V
POWER
=V
OUT
+ 0.8V, I
LOAD
= 3A
V
CONTROL
=V
OUT
+ 2.5V, I
LOAD
= 10mA
V
CONTROL
=V
OUT
+ 2.5V, I
LOAD
= 2A
V
CONTROL
=V
OUT
+ 2.5V, I
LOAD
= 3A
Min
Typ
Max
Units
1.00
1.15
0.10
0.30
0.35
1.15
1.30
0.17
0.45
0.50
V
V
V
V
V
Parameters identified with
boldface type
apply over the full operating temperature range.
Note 1:
Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. For guaranteed specifications and test conditions, see the
Electrical Characteristics
.
The guaranteed specifications apply only for the test conditions listed.
Note 2:
Unless otherwise specified V
OUT
= V
SENSE
. For the adjustable device V
ADJ
= 0V.
Note 3:
The dropout voltage for the AMS1503 is caused by either minimum control voltage or minimum power voltage. The specifications represent the
minimum input/output voltage required to maintain 1% regulation.
Note 4:
For the adjustable device the minimum load current is the minimum current required to maintain regulation. Normally the current in the resistor
divider used to set the output voltage is selected to meet the minimum load current requirement.
Note 5:
The control pin current is the drive current required for the output transistor. This current will track output current with a ratio of about 1:100. The
minimum value is equal to the quiescent current of the device.
PIN FUNCTIONS
Sense (Pin 1):
This pin is the positive side of the reference
voltage for the device. With this pin it is possible to Kelvin
sense the output voltage at the load.
Adjust (Pin 2/5):
This pin is the negative side of the
reference voltage for the device. Adding a small bypass
capacitor from the Adjust pin to ground improves the
transient response. For fixed voltage devices the Adjust
pin is also brought out to allow the user to add a bypass
capacitor.
GND (Pin 2/5):
For fixed voltage devices this is the
bottom of the resistor divider that sets the output voltage.
V
POWER
(Pin 5/6):
This pin is the collector to the power
device of the AMS1503. The output load current is
supplied through this pin. The voltage at this pin must
be between 0.1V and 0.8V greater than the output
voltage for the device to regulate.
V
CONTROL
(Pin 4/3):
This pin is the supply pin for the
control circuitry of the device. The current flow into
this pin will be about 1% of the output current. The
voltage at this pin must be 1.3V or greater than the
output voltage for the device to regulate.
Output (Pin 3/4):
This is the power output of the
device.
Advanced Monolithic Systems, Inc.
www.advanced-monolithic.com
Phone (925) 443-0722
Fax (925) 443-0723
AMS1503
APPLICATION HINTS
The AMS1503 series of adjustable and fixed regulators are
designed to power the new generation of microprocessors. The
AMS1503 is designed to make use of multiple power supplies,
existing in most systems, to reduce the dropout voltage. One of the
advantages of the two supply approach is maximizing the
efficiency.
The second supply is at least 1V greater than output voltage and is
providing the power for the control circuitry and supplies the drive
current to the NPN output transistor. This allows the NPN to be
driven into saturation; thereby reducing the dropout voltage by a
VBE compared to conventional designs. For the control voltage
the current requirement is small equal to about 1% of the output
current or approximately 30mA for a 3A load. Most of this current
is drive current for the NPN output transistor. This drive current
becomes part of the output current. The maximum voltage on the
Control pin is 13V. The maximum voltage at the Power pin is 7V.
Ground pin current for fixed voltage devices is typical 6mA and is
constant as a function of load. Adjust pin current for adjustable
devices is 60µA at 25°C and varies proportional to absolute
temperature.
The improved frequency compensation of AMS1503 permits the
use of capacitors with very low ESR. This is critical in addressing
the needs of modern, low voltage high sped microprocessors. The
new generation of microprocessors cycle load current from several
hundred mA to several A in tens of nanoseconds. Output voltage
tolerances are tighter and include transient response as part of the
specification. Designed to meet the fast current load step
requirements of these microprocessors, the AMS1503 also saves
total cost by needing less output capacitance to maintain
regulation.
Careful design of the AMS1503 has eliminated any supply
sequencing issues associated with a dual supply system. The
output voltage will not turn on until both supplies are operating. If
the control voltage comes up first, the output current will be
limited to a few milliamperes until the power input voltage comes
up. If power input comes up first the output will not turn on at all
until the control voltage comes up. The output can never come up
unregulated. By tying the control and power inputs together the
AMS1503 can also be operated as a single supply device. In single
supply operation the dropout will be determined by the minimum
control voltage.
The new features of the AMS1503 require additional pins over the
traditional 3-terminal regulator. Both the fixed and adjustable
versions have remote sense pins, permitting very accurate
regulation of output voltage at the load, rather than at the
regulator. As a result, over an output current range of 100mA to
3A with a 2.5V output, the typical load regulation is less than
1mV. For the fixed voltages the adjust pin is brought out allowing
the user to improve transient response by bypassing the internal
resistor divider. Optimum transient response is provided using a
capacitor in the range of 0.1µF to 1µF for bypassing the Adjust
pin. The value chosen will depend on the amount of output
capacitance in the system.
In addition to the enhancements mentioned, the reference accuracy
has been improved by a factor of two with a guaranteed initial
tolerance of
±0.6%
at 25°C. This device can hold 1% accuracy
over the full temperature range and load current range,
guaranteed, when combined with ratiometrically accurate internal
divider resistors and operating with an input/output differential of
well under 1V.
Typical applications for the AMS1503 include 3.3V to 2.5V
conversion with a 5V control supply, 5V to 4.2V conversion with
a 12V control supply or 5V to 3.6V conversion with a 12V control
supply. Capable of 3A of output current with a maximum dropout
of 0.8V the AMS1503 also has a fast transient response that
allows it to handle large current changes associated with the new
generation of microprocessors. The device is fully protected
against overcurrent and overtemperature conditions.
Grounding and Output Sensing
The AMS1503 allows true Kelvin sensing for both the high and
low side of the load. As a result the voltage regulation at he load
can be easily optimized. Voltage drops due to parasitic resistances
between the regulator and the load can be placed inside the
regulation loop of the AMS1503. The advantages of remote
sensing are illustrated in figures 1 through 3.
Figure 1 shows the device connected as a conventional 3 terminal
regulator with the Sense lead connected directly to the output of
the device. R
P
is the parasitic resistance of the connections
between the device and the load. Typically the load is a
microprocessor and R
P
is made up of the PC traces and /or
connector resistances (in the case of a modular regulator) between
the regulator and the processor. Trace A of figure 3 illustrates the
effect of RP. Very small resistances cause significant load
regulation steps.
Figure 2 shows the device connected to take advantage of the
remote sense feature. The Sense pin and the top of the resistor
divider are connected to the top of the load; the bottom of the
resistor divider is connected to the bottom of the load. R
P
is now
connected inside the regulation loop of the AMS1503 and for
reasonable values of R
P
the load regulation at the load will be
negligible. The effect on output regulation can be seen in trace B
of figure 3.
5V
CONTROL
POWER
SENSE
3.3V
AMS1503
OUTPUT
ADJ
R
P
LOAD
R1
R2
R
P
+
V
OUT
-
Figure 1. Conventional Load Sensing
Advanced Monolithic Systems, Inc.
www.advanced-monolithic.com
Phone (925) 443-0722
Fax (925) 443-0723
AMS1503
APPLICATION HINTS
5V
CONTROL
POWER
SENSE
3.3V
AMS1503
OUTPUT
ADJ
R
P
LOAD
R1
R2
R
P
+
V
OUT
-
Figure 2. Remote Load Sensing
(∆I
OUT
)(R
P
)
V
OUT
FIGURE 1
V
OUT
FIGURE 2
to allow this capability. To ensure good transient response with
heavy load current changes capacitor values on the order of 100µF
are used in the output of many regulators. To further improve
stability and transient response of these devices larger values of
output capacitor can be used.
The modern processors generate large high frequency current
transients. The load current step contains higher order frequency
components than the output coupling network must handle until
the regulator throttles to the load current level. Because they
contain parasitic resistance and inductance, capacitors are not
ideal elements. These parasitic elements dominate the change in
output voltage at the beginning of a transient load step change.
The ESR of the output capacitors produces an instantaneous step
in output voltage (∆V=∆I)(ESR). The ESL of the output
capacitors produces a droop proportional to the rate of change of
the output current (V= L)(∆I/∆t). The output capacitance produces
a change in output voltage proportional to the time until the
regulator can respond (∆V=∆t) (∆I/C). Figure 4 illustrates these
transient effects.
ESR
EFFECTS
ESL
EFFECTS
SLOPE, V/t =
∆I/C
CAPACITANCE
EFFECTS
I
OUT
TIME
POINT AT WHICH REGULATOR
TAKES CONTROL
Figure 4.
Output Voltage
The AMS1503 series develops a 1.25V reference voltage between
the Sense pin and the Adjust pin (Figure5). Placing a resistor
between these two terminals causes a constant current to flow
through R1 and down through R2 to set the overall output voltage.
In general R1 is chosen so that this current is the specified
minimum load current of 10mA.The current out of the Adjust pin
is small, typically 50µA and it adds to the current from R1.
Because I
ADJ
is very small it needs to be considered only when
very precise output voltage setting is required. For best regulation
the top of the resistor divider should be connected directly to the
Sense pin.
V
CONTROL
+
CONTROL
POWER
OUTPUT
Figure 3. Remote Sensing Improves Load Regulation
Voltage drops due to R
P
are not eliminated; they will add to the
dropout voltage of the regulator regardless of whether they are
inside or outside the regulation loop. The AMS1503 can control
the voltage at the load as long as the input-output voltage is
greater than the total of the dropout voltage of the device plus the
voltage drop across R
P
.
Stability
The circuit design used in the AMS1503 series requires the use of
an output capacitor as part of the device frequency compensation.
The addition of
150
µF
aluminum electrolytic or a 22µF solid
tantalum on the output will ensure stability for all operating
conditions. For best frequency response use capacitors with an
ESR of less than 1Ω.
In order to meet the transient requirements of the processor larger
value capacitors are needed. Tight voltage tolerances are required
in the power supply. To limit the high frequency noise generated
by the processor high quality bypass capacitors must be used. In
order to limit parasitic inductance (ESL) and resistance (ESR) in
the capacitors to acceptable limits, multiple small ceramic
capacitors in addition to high quality solid tantalum capacitors are
required.
When the adjustment terminal is bypassed to improve the ripple
rejection, the requirement for an output capacitor increases. The
Adjust pin is brought out on the fixed voltage device specifically
