Advanced Monolithic Systems, Inc. 6680B Sierra Lane, Dublin, CA 94568 Phone (925) 556-9090 Fax (925) 556-9140
Advanced
AMS1505V
Monolithic
5A ULTRA LOW DROPOUT VOLTAGE REGULATORS
Systems
FEATURES
APPLICATIONS
Adjustable or Fixed Output
High Speed Video/Graphic Cards
1.5V, 2.5V, 2.85V, 3.0V, 3.3V, 3.5V and 5.0V
Post Regulators for Switching Supplies
Output Current of 5A
Microprocessor Supply
Low Dropout, 350mV max. at 5A Output Current
Adjustable Power Supply
Fast Transient Response
Notebook/Personal Computer Supplies
Remote Sense
High Current Regulators
GENERAL DESCRIPTION
The
Designed specially for video applications where a very low dropout is critical, the AMS1505V series of adjustable and fixed
low dropout voltage regulators provide 5A output current to power the new generation of high speed video cards. The dropout
voltage of the device is 200mV max. at 3A loads and rising to 350mV at maximum output current. A second low current
input voltage 1V or greater then the output voltage is required to achieve this dropout.
New features have been added to the AMS1505V: 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 5A
is less than 1mV. The AMS1505V series has fast transient response. To further improve the transient response the addition of
a small capacitor on the Adjust pin is recommended.
The AMS1505V series are ideal for generating supplies of 2V to 3V on boards where both 5V and 3.3V supplies are
available.
The AMS1505V devices are offered in 5 lead TO-220 and TO-263 (plastic DD) packages.
ORDERING INFORMATION:
PIN CONNECTIONS
PACKAGE TYPE
OPERATING
5 LEAD TO-263
5 LEAD TO-220
TEMPERATURE RANGE
AMS1505CMV
AMS1505CTV
0 to 125
C
AMS1505CMV-1.5 AMS1505CTV-1.5
0 to 125
C
AMS1505CMV-2.5 AMS1505CTV-2.5
0 to 125
C
AMS1505CMV-2.85 AMS1505CTV-2.85
0 to 125
C
AMS1505CMV-3.0 AMS1505CTV-3.0
0 to 125
C
AMS1505CMV-3.3 AMS1505CTV-3.3
0 to 125
C
AMS1505CMV-3.5 AMS1505CTV-3.5
0 to 125
C
AMS1505CMV-5.0 AMS1505CTV-5.0
0 to 125
C
5
4
3
2
1
Vpower
Vcontrol
OUTPUT
ADJUST/GND
SENSE
FRONT VIEW
5 LEAD TO-263
5
4
3
2
1
V
POWER
V
CONTROL
OUTPUT
ADJUST/GND
SENSE
FRONT VIEW
5 LEAD TO-220
Advanced Monolithic Systems, Inc. 6680B Sierra Lane, Dublin, CA 94568 Phone (925) 556-9090 Fax (925) 556-9140
AMS1505V
ABSOLUTE MAXIMUM RATINGS
(Note 1)
V
POWER
Input Voltage
7V
Soldering information
V
CONTROL
Input Voltage
13V
Lead Temperature (10 sec)
300
C
Operating Junction Temperature Range
Thermal Resistance
Control Section
0
C to 125
C
TO-220 package
JA
= 50
C/W
Power Transistor
0
C to 150
C
TO-263 package
JA
= 30
C/W*
Storage temperature
- 65
C to +150
C
* With package soldering to 0.5in
2
copper area over backside ground
plane or internal power plane
JA
can vary from 20
C/W to
>
40
C/W
depending on mounting technique.
ELECTRICAL CHARACTERISTICS
Electrical Characteristics at I
LOAD
= 0 mA, and T
J
= +25C unless otherwise specified.
Parameter
Device
Conditions
Min Typ Max
Units
Reference Voltage
AMS1505V
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 5A
1.238
1.250
1.262
V
Output Voltage
AMS1505V-1.5
V
CONTROL
= 4V, V
POWER
=2.V, I
LOAD
= 0mA
V
CONTROL
= 3V, V
POWER
=2.3V, I
LOAD
= 0mA to 5A
1.485
1.500
1.515
V
AMS1505V-2.5
V
CONTROL
= 5V, V
POWER
=3.3V, I
LOAD
= 0mA
V
CONTROL
= 4V, V
POWER
=3.3V, I
LOAD
= 0mA to 5A
2.475
2.500
2.525
V
AMS1505V-2.85
V
CONTROL
= 5.35V, V
POWER
=3.35V, I
LOAD
= 0mA
V
CONTROL
= 4.4V, V
POWER
=3.7V, I
LOAD
= 0mA to 5A
2.833
2.850
2.867
V
AMS1505V-3.0
V
CONTROL
= 5.5V, V
POWER
=3.5V, I
LOAD
= 0mA
V
CONTROL
= 4.5V, V
POWER
=3.8V, I
LOAD
= 0mA to 5A
2.970
3.000
3.030
V
AMS1505V-3.3
V
CONTROL
= 5.8V, V
POWER
=3.8V, I
LOAD
= 0mA
V
CONTROL
= 4.8V, V
POWER
=4.1V, I
LOAD
= 0mA to 5A
3.235
3.300
3.333
V
AMS1505V-3.5
V
CONTROL
= 6V, V
POWER
=4V, I
LOAD
= 0mA
V
CONTROL
= 5V, V
POWER
=4.3V, I
LOAD
= 0mA to 5A
3.430
3.500
3.535
V
AMS1505V-5.0
V
CONTROL
= 7.5V, V
POWER
=5.5V, I
LOAD
= 0mA
V
CONTROL
= 6.5V, V
POWER
=5.8V, I
LOAD
= 0mA to 5A
4.950
5.000
5.030
V
Line Regulation
AMS1505V/-1.5/-2.5/
-2.85/-3.0/-3.3/-3.5/-5.0
I
LOAD
= 10 mA , 1.5V
(V
CONTROL
- V
OUT
)
12V
0.8V
(V
POWER
- V
OUT
)
5.5V
1
3
mV
Load Regulation
AMS1505V/-1.5/-2.5/
-2.85/-3.0/-3.3/-3.5/-5.0
V
CONTROL
= V
OUT
+ 2.5V, V
POWER
=V
OUT
+ 0.8V,
I
LOAD
= 10mA to 5A
1
5
mV
Minimum Load
Current
AMS1505V
V
CONTROL
= 5V, V
POWER
=3.3V, V
ADJ
= 0V (Note 3)
5
10
mA
Control Pin Current
(Note 4)
AMS1505V/-1.5/-2.5/
-2.85/-3.0/-3.3/-3.5/-5.0
V
CONTROL
= V
OUT
+ 2.5V, V
POWER
=V
OUT
+ 0.8V,
I
LOAD
= 10mA to 5A
50
85
mA
Ground Pin Current
(Note 4)
AMS1505V/-1.5/-2.5/
-2.85/-3.0/-3.3/-3.5/-5.0
V
CONTROL
= V
OUT
+ 2.5V, V
POWER
=V
OUT
+ 0.8V,
I
LOAD
= 10mA to 5A
6
10
mA
Adjust Pin Current
AMS1505V
V
CONTROL
= 2.75V, V
POWER
= 2.05V, I
LOAD
= 10mA
50
120
A
Ripple Rejection
AMS1505V/-1.5/-2.5/
-2.85/-3.0/-3.3/-3.5/-5.0
V
CONTROL
= V
POWER
= V
OUT
+ 2.5V, V
RIPPLE
= 1V
P-P
I
LOAD
= 2A
60
80
dB
Thermal Regulation
AMS1505V
T
A
= 25C, 30ms pulse
0.002
0.020
%W
Thermal Resistance
Junction-to-Case
T Package: Control Circuitry/ Power Transistor
M Package: Control Circuitry/ Power Transistor
0.65/2.70
0.65/2.70
C/W
C/W
Advanced Monolithic Systems, Inc. 6680B Sierra Lane, Dublin, CA 94568 Phone (925) 556-9090 Fax (925) 556-9140
AMS1505V
ELECTRICAL CHARACTERISTICS
Electrical Characteristics at I
OUT
= 0 mA, and T
J
= +25C unless otherwise specified.
Parameter
Device
Conditions
Min Typ Max
Units
Dropout Voltage
Note 2
Control Dropout
(V
CONTROL
- V
OUT
)
AMS1505V/-1.5/-2.5/
-2.85/-3.0/-3.3/-3.5/-5.0
V
POWER
=V
OUT
+ 0.8V, I
LOAD
= 10mA
V
POWER
=V
OUT
+ 0.8V, I
LOAD
= 5A
1.00
1.15
1.20
1.30
V
V
Power Dropout
(V
POWER
- V
OUT
)
AMS1505V/-1.5/-2.5/
-2.85/-3.0/-3.3/-3.5/-5.0
V
CONTROL
=V
OUT
+ 2.5V, I
LOAD
= 3A
V
CONTROL
=V
OUT
+ 2.5V, I
LOAD
= 5A
175
300
200
350
mV
mV
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 AMS1505V is caused by either minimum control voltage or minimum power voltage. The specifications represent the
minimum input/output voltage required to maintain within 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/Ground (Pin 2): 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.
Output (Pin 3): This is the power output of the device.
V
CONTROL
(Pin 4): 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.
V
POWER
(Pin 5): This pin is the collector to the power
device of the AMS1505V. The output load current is
supplied through this pin. The voltage at this pin must
be between 0.1V and 0.35V greater than the output
voltage for the device to regulate.
Advanced Monolithic Systems, Inc. 6680B Sierra Lane, Dublin, CA 94568 Phone (925) 556-9090 Fax (925) 556-9140
AMS1505V
APPLICATION HINTS
The AMS1505V series of adjustable and fixed regulators are
designed to power the new generation of microprocessors. The
AMS1505V 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 0.35V 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 50mA for a 5A 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 60
A at 25
C
and varies proportional to absolute temperature.
The improved frequency compensation of AMS1505V 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 the video-processors, the AMS1505V also saves
total cost by needing less output capacitance to maintain
regulation.
Careful design of the AMS1505V 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.
The new features of the AMS1505V 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
5A with a 2.5V output, the typical load regulation is less than
1mV. Optimum transient response is provided using a capacitor
in the range of 0.1
F to 1
F 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
1% 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 AMS1505V include 3.3V to 2.9V
conversion with a 5V control supply, 5V to 4.7V conversion with
a 12V control supply or 5V to 3.6V conversion with a 12V
control supply. Capable of 5A of output current with a maximum
dropout of 350mV the AMS1505V also has a fast transient
response that allows it to handle large current changes associated
with the new generation of video-processors. The device is fully
protected against overcurrent and overtemperature conditions.
Grounding and Output Sensing
The AMS1505V 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 AMS1505V. 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 AMS1505V 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.
CONTROL
POWER
SENSE
AMS1505V
OUTPUT
ADJ
LOAD
+
-
V
OUT
R
P
R
P
R1
R2
5V
3.3V
Figure 1. Conventional Load Sensing
Advanced Monolithic Systems, Inc. 6680B Sierra Lane, Dublin, CA 94568 Phone (925) 556-9090 Fax (925) 556-9140
AMS1505V
APPLICATION HINTS
CONTROL
POWER
SENSE
AMS1505V
OUTPUT
ADJ
LOAD
+
-
V
OUT
R
P
R
P
R1
R2
5V
3.3V
Figure 2. Remote Load Sensing
(
I
OUT
)(R
P
)
TIME
V
OUT
FIGURE 1
V
OUT
FIGURE 2
I
OUT
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 AMS1505V 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 AMS1505V series requires the use
of an output capacitor as part of the device frequency
compensation. The addition of
150
F aluminum electrolytic or a
22
F solid tantalum on the output will ensure stability for all
operating conditions. For best frequency response use capacitors
with an ESR of less than 1
.
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
to allow this capability. To ensure good transient response with
heavy load current changes capacitor values on the order of
100
F 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.
CAPACITANCE
EFFECTS
ESR
EFFECTS
ESL
EFFECTS
POINT AT WHICH REGULATOR
TAKES CONTROL
SLOPE, V/t =
I/C
Figure 4.
Output Voltage
The AMS1505V 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 50
A 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.
CONTROL
POWER
OUTPUT
AMS1505V
SENSE
ADJ
R1
R2
V
OUT
V
REF
V
POWER
I
ADJ
50
A
+
+
+
V
CONTROL
V
OUT
= V
REF
(
1+ R2/R1)+I
ADJ
R2
Figure 5. Setting Output Voltage
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