AMS2501 - Advanced Monolithic Systems

Advanced
Monolithic
Systems
AMS2501
1A VERY LOW DROPOUT VOLTAGE REGULATOR
RoHS compliant
FEATURES
APPLICATIONS
• Adjustable or Fixed Output
1.5V, 1.8V, 2.5V, 2.85V, 3.0V, 3.3V, 3.5V and 5.0V
• Output Current of 1A
• Low Dropout, typ. 200mV at 500mA Output Current
• Fast Transient Response
• Remote Sense
• High Efficiency Current Regulators
• Post Regulators for Switching Supplies
• Audio/Video/Modem Card Supply
• Adjustable Power Supply
• Notebook/Personal Computer Supplies
GENERAL DESCRIPTION
The
The AMS2501 series are adjustable and fixed low dropout voltage regulators are designed to provide 1A output current. The
dropout voltage of the device is 100mV at light loads and rising to 200mV at 500mA output current. A second input voltage of
1.2V or greater than the output is required to achieve this dropout. The AMS2501 can also be used as a single supply device by
connecting pin1 and pin 8 together. In this case the dropout voltage will be typically 1.2V.
New features have been added to the AMS2501: 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 1A
is less than 1mV. The AMS2501 series has fast transient response and are ideal for generating supplies of 1.25V to 3V where
both 5V and 3.3V supplies are available.
The AMS2501 devices are offered in 8 lead EDP package.
ORDERING INFORMATION:
OPERATING
JUNCTION
AMS2501CS
AMS2501CS-1.5
AMS2501CS-1.8
AMS2501CS-2.5
AMS2501CS-2.85
AMS2501CS-3.0
AMS2501CS-3.3
AMS2501CS-3.5
AMS2501CS-5.0
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TEMPERATURE
RANGE
0 to 125° C
0 to 125° C
0 to 125° C
0 to 125° C
0 to 125° C
0 to 125° C
0 to 125° C
0 to 125° C
0 to 125° C
PIN CONNECTIONS
AMS2501 8L SOIC EDP
POWER IN 1
8 CONTROL IN
OUTPUT 2
7 N/C
OUTPUT 3
6 ADJ/GND
SENSE
4
5 N/C
Top View
updated April 24, 2009
AMS2501
ABSOLUTE MAXIMUM RATINGS (Note 1)
VPOWER Input Voltage
VCONTROL Input Voltage
Operating Junction Temperature Range
Control Section
Power Transistor
Storage temperature
7V
13V
0°C to 125°C
0°C to 150°C
- 65°C to +150°C
Soldering information
Lead Temperature (25 sec)
Thermal Resistance
SO-8 package
265°C
ϕ JA= 60°C/W
ELECTRICAL CHARACTERISTICS
Electrical Characteristics at ILOAD = 0 mA, and TJ = +25°C unless otherwise specified.
Parameter
Device
Conditions
Reference Voltage
AMS2501
VCONTROL = 2.75V, VPOWER =2V, ILOAD = 10mA
VCONTROL = 2.7V to 12V, VPOWER =3.3V to 5.5V,
ILOAD = 10mA to 1A
1.238
1.232
Output Voltage
AMS2501-1.5
VCONTROL = 4V, VPOWER =2.V, ILOAD = 0mA
VCONTROL = 3V, VPOWER =2.3V, ILOAD = 0mA to 1A
AMS2501-1.8
Line Regulation
Min
Typ
Max
Units
1.250
1.250
1.262
1.268
V
V
1.491
1.485
1.500
1.500
1.509
1.515
V
V
VCONTROL = 4V, VPOWER =2.V, ILOAD = 0mA
VCONTROL = 3V, VPOWER =2.3V, ILOAD = 0mA to 1A
1.782
1.773
1.800
1.800
1.818
1.827
V
V
AMS2501-2.5
VCONTROL = 5V, VPOWER =3.3V, ILOAD = 0mA
VCONTROL = 4V, VPOWER =3.3V, ILOAD = 0mA to 1A
2.485
2.475
2.500
2.500
2.515
2.525
V
V
AMS2501-2.85
VCONTROL = 5.35V, VPOWER =3.35V, ILOAD = 0mA
VCONTROL = 4.4V, VPOWER =3.7V, ILOAD = 0mA to
1A
2.821
2.833
2.850
2.850
2.879
2.867
V
V
AMS2501-3.0
VCONTROL = 5.5V, VPOWER =3.5V, ILOAD = 0mA
VCONTROL = 4.5V, VPOWER =3.8V, ILOAD = 0mA to
1A
2.982
2.970
3.000
3.000
3.018
3.030
V
V
AMS2501-3.3
VCONTROL = 5.8V, VPOWER =3.8V, ILOAD = 0mA
VCONTROL = 4.8V, VPOWER =4.1V, ILOAD = 0mA to
1A
3.280
3.235
3.300
3.300
3.320
3.333
V
V
AMS2501-3.5
VCONTROL = 6V, VPOWER =4V, ILOAD = 0mA
VCONTROL = 5V, VPOWER =4.3V, ILOAD = 0mA to 1A
3.479
3.430
3.500
3.500
3.521
3.535
V
V
AMS2501-5.0
VCONTROL = 7.5V, VPOWER =5.5V, ILOAD = 0mA
VCONTROL = 6.5V, VPOWER =5.8V, ILOAD = 0mA to
1A
4.930
4.950
5.000
5.000
5.030
5.050
V
V
AMS2501-1.5/-1.8/-2.5/2.85/-3.0/-3.3/-3.5/-5.0
ILOAD = 10 mA , 1.5V≤ (VCONTROL - VOUT) ≤ 12V
1
3
mV
1
5
mV
0.8V≤ (VPOWER - VOUT) ≤ 5.5V
Load Regulation
AMS2501-1.5/-1.8/-2.5/2.85/-3.0/-3.3/-3.5/-5.0
VCONTROL = VOUT + 2.5V, VPOWER =VOUT + 0.8V,
Minimum Load
Current
AMS2501
VCONTROL = 5V, VPOWER =3.3V, VADJ = 0V (Note 3)
5
10
mA
Control Pin Current
AMS2501-1.5/-1.8/-2.5/2.85/-3.0/-3.3/-3.5/-5.0
VCONTROL = VOUT + 2.5V, VPOWER =VOUT + 0.8V,
10
16
mA
VCONTROL = VOUT + 2.5V, VPOWER =VOUT + 0.8V,
6
10
mA
(Note 4)
AMS2501-1.5/-1.8/-2.5/2.85/-3.0/-3.3/-3.5/-5.0
Adjust Pin Current
AMS2501
VCONTROL = 2.75V, VPOWER = 2.05V, ILOAD = 10mA
40
120
µA
Current Limit
AMS2501-1.5/-1.8/-2.5/2.85/-3.0/-3.3/-3.5/-5.0
VPOWER =VOUT + 0.8V
1.0
1.2
1.5
A
Ripple Rejection
AMS2501-1.5/-1.8/-2.5/2.85/-3.0/-3.3/-3.5/-5.0
VCONTROL = VPOWER = VOUT + 2.5V, VRIPPLE = 1VP-P
60
80
(Note 4)
Ground Pin Current
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ILOAD = 10mA to 1A
ILOAD = 10mA
ILOAD = 10mA
ILOAD = 1A
updated April 24, 2009
dB
AMS2501
ELECTRICAL CHARACTERISTICS
Electrical Characteristics at IOUT = 0 mA, and TJ = +25°C unless otherwise specified.
Parameter
Device
Conditions
Min
Thermal Regulation
AMS2501
TA = 25°C, 30ms pulse, ILOAD = 1A
Typ
Max
Units
0.002
0.020
%W
VPOWER =VOUT + 0.8V, ILOAD = 10mA
1.00
1.15
V
VPOWER =VOUT + 0.8V, ILOAD = 1A
1.15
1.30
V
VCONTROL =VOUT + 2.5V, ILOAD = 1A
.05
0.15
V
.30
0.50
V
Note 2
Dropout Voltage
Control Dropout
(VCONTROL - VOUT)
AMS2501-1.5/-1.8/-2.5/2.85/-3.0/-3.3/-3.5/-5.0
Power Dropout
(VPOWER - VOUT)
AMS2501-1.5/-1.8/-2.5/2.85/-3.0/-3.3/-3.5/-5.0
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 VOUT = VSENSE. For the adjustable device VADJ = 0V.
Note 3: The dropout voltage for the AMS2501 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
VPOWER (Pin 1): This pin is the collector to the power
device of the AMS2501. 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.
Adjust (Pin 6): 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.
Output (Pin 2 and 3): These are the power output of the
device. Pin 2 and 3 are fused together and with the package
paddle serving also as heat sink.
N/C (Pin 7): Not Connect.
Sense (Pin 4): 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.
VCONTROL (Pin 8): 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 between 1.0V and 1.3V greater than
the output voltage for the device to regulate.
N/C (Pin 5): Not Connect.
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updated April 24, 2009
AMS2501
APPLICATION HINTS
The AMS2501 series of adjustable and fixed regulators 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 1.2V 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 10mA for a 1A 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 40µA at 25°C and varies proportional to absolute
temperature.
The improved frequency compensation of AMS2501 permits the
use of capacitors with very low ESR. Output voltage tolerances are
tighter and include transient response as part of the specification.
Designed to meet the fast current load step, the AMS2501 also
saves total cost by needing less output capacitance to maintain
regulation.
Careful design of the AMS2501 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
AMS2501 can also be operated as a single supply device. In single
supply operation the dropout will be determined by the minimum
control voltage.
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 1A 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 0.1µF to 1µF for
bypassing the Reference pin. The value chosen will depend on the
amount of output capacitance in the system.
This devices 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 AMS2501 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 1A of output current with a maximum
dropout of 0.8V the AMS2501 also has a fast transient response
that allows it to handle large current changes. The device is fully
protected against overcurrent and overtemperature conditions.
Grounding and Output Sensing
The AMS2501 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 AMS2501. 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. RP is the parasitic resistance of the connections
between the device and the load. RP is made up of the PCB traces
and /or connector resistances (in the case of a modular regulator)
between the regulator and the load. 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. RP is now
connected inside the regulation loop of the AMS2501 and for
reasonable values of RP the load regulation at the load will be
negligible. The effect on output regulation can be seen in trace B
of figure 3.
5V
3.3V
CONTROL
POWER
SENSE
AMS2501
OUTPUT
ADJ
+
RP
LOAD
R1
R2
RP
VOUT
-
Figure 1. Conventional Load Sensing
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updated April 24, 2009
AMS2501
APPLICATION HINTS
5V
3.3V
CONTROL
POWER
SENSE
AMS2501
OUTPUT
ADJ
+
RP
LOAD
R1
R2
RP
VOUT
-
Some of the loads 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.
Figure 2. Remote Load Sensing
ESR
EFFECTS
(∆IOUT)(RP)
VOUT
FIGURE 1
ESL
EFFECTS
CAPACITANCE
EFFECTS
SLOPE, V/t = ∆I/C
VOUT
FIGURE 2
POINT AT WHICH REGULATOR
TAKES CONTROL
Figure 4.
IOUT
Output Voltage
TIME
Figure 3. Remote Sensing Improves Load Regulation
Voltage drops due to RP 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 AMS2501 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 RP.
The AMS2501 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 40µA and it adds to the current from R1.
Because IADJ 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.
Stability
The circuit design used in the AMS2501 series requires the use of
an output capacitor as part of the device frequency compensation.
The addition of 150µF 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 increase the transient response larger value capacitors
are needed. To limit the high frequency noise generated by the
load 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
reference voltage is brought out specifically to allow this
capability.
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VCONTROL
+
CONTROL
POWER
OUTPUT
VPOWER
+
+
AMS2501
SENSE
ADJ
VREF
R1
IADJ
50µA
R2
VOUT = VREF (1+ R2/R1)+IADJR2
Figure 5. Setting Output Voltage
updated April 24, 2009
VOUT
AMS2501
APPLICATION HINTS
Protection Diodes
Unlike older regulators, the AMS2501 family does not need any
protection diodes between the adjustment pin and the output and
from the output to the input to prevent die over-stress. Internal
resistors are limiting the internal current paths on the AMS2501
adjustment pin, therefore even with bypass capacitors on the adjust
pin no protection diode is needed to ensure device safety under
short-circuit conditions. The Adjust pin can be driven on a
transient basis ±7V with respect to the output without any device
degradation.
Diodes between the Output pin and VPOWER pin are not usually
needed. Microsecond surge currents of 10A to 25A can be handled
by the internal diode between the Output pin and VPOWER pin of
the device. In normal operations it is difficult to get those values of
surge currents even with the use of large output capacitances. If
high value output capacitors are used, such as 1000µF to 5000µF
and the VPOWER pin is instantaneously shorted to ground, damage
can occur. A diode from output to input is recommended, when a
crowbar circuit at the input of the AMS2501 is used (Figure 6).
Normal power supply cycling or even plugging and unplugging in
the system will not generate current large enough to do any
damage.
D1*
D2*
CONTROL
POWER
OUTPUT
VPOWER
+
AMS2501
SENSE
ADJ
The power in the drive circuit is equal to:
PDRIVE = (VCONTROL - VOUT)(ICONTROL)
where ICONTROL is equal to between IOUT/100(typ) and
IOUT/60(max).
The power in the output transistor is equal to:
VCONTROL
+
Control section can run up to 125°C, and the Power section can
run up to 150°C. Due to the thermal gradients between the power
transistor and the control circuitry there is a significant difference
in thermal resistance between the Control and Power sections.
Virtually all the power dissipated by the device is dissipated in the
power transistor. The temperature rise in the power transistor will
be greater than the temperature rise in the Control section making
the thermal resistance lower in the Control section. At power
levels below 0.5W the temperature gradient will be less than 25°C
and the maximum ambient temperature will be determined by the
junction temperature of the Control section. This is due to the
lower maximum junction temperature in the Control section. At
power levels above 0.5W the temperature gradient will be greater
than 25°C and the maximum ambient temperature will be
determined by the Power section. In both cases the junction
temperature is determined by the total power dissipated in the
device. For most low dropout applications the power dissipation
will be less than 0.5W.
The power in the device is made up of two components: the power
in the output transistor and the power in the drive circuit. The
power in the control circuit is negligible.
+
VOUT
POUTPUT = (VPOWER -VOUT)(IOUT)
The total power is equal to:
R1
R2
Figure 6. Optional Clamp Diodes Protect Against
Input Crowbar Circuits
PTOTAL = PDRIVE + POUTPUT
Junction-to-case thermal resistance is specified from the IC
junction to the bottom of the case directly below the die. This is
the lowest resistance path for the heat flow. In order to ensure the
best possible thermal flow from this area of the package to the
PCB proper mounting is required.
If the AMS2501 is connected as a single supply device with the
control and power input pins shorted together the internal diode
between the output and the power input pin will protect the control
input pin. As with any IC regulator, none the protection circuitry
will be functional and the internal transistors will break down if
the maximum input to output voltage differential is exceeded.
Thermal Considerations
The AMS2501 series have internal power and thermal limiting
circuitry designed to protect the device under overload conditions.
However maximum junction temperature ratings should not be
exceeded under continuous normal load conditions. Careful
consideration must be given to all sources of thermal resistance
from junction to ambient.
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updated April 24, 2009
AMS2501
TYPICAL PERFORMANCE CHARACTERISTICS
Control Pin Current vs
Output Current
25
20
TYPICAL
DEVICE
15
10
5
MINMUM CONTROL VOLTAGE
(VCONTROL - VOUT)(V)
30
1.0
1
T J = 125° C
MINIMUM POWER VOLTAGE
2
35
CONTROL PIN CURRENT (mA)
Dropout Voltage Minimum Power Voltage
Minimum Control Voltage
T J = 25° C
0
0
0
0.2 0.4 0.6 0.8 1.0 1.2 1.4
OUTPUT CURRENT (A)
0.5
T J = 125° C
T J = 25° C
0
0
0.2 0.4 0.6 0.8 1.0 1.2 1.4
OUTPUT CURRENT (A)
Reference Voltage vs
Temperature
0
0.2
0.4 0.6 0.8 1.0 1.2 1.4
OUTPUT CURRENT (A)
Load Current Step Response
REFERENCE VOLTAGE (V)
1.258
1.256
VOUT
50µV/DIV
1.254
1.252
1.250
1.5A
1.248
1.246
LOAD
1.244
1.242
-50 -25
400mA
0 25 50 75 100 125 150
TEMPERATURE (° C)
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50µ/DIV
updated April 24, 2009
AMS2501
PACKAGE DIMENSIONS inches (millimeters) unless otherwise noted.
8 LEAD SOIC PLASTIC PACKAGE (S)
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updated April 24, 2009