AS2815
1.5A Low Dropout Voltage Regulator
Adjustable & Fixed Output,
Fast Response
FEATURES
•
Adjustable Output Down To 1.2V
•
Fixed Output Voltages 1.5V, 2.5V, 3.3V, 5.0V
•
Output Current of 1.5A
•
Low Dropout Voltage 1.1V Typ.
•
Extremely Tight Load And Line Regulation
•
Current & Thermal Limiting
•
Standard 3-Terminal Low Cost TO-220, TO-263 & TO-252
•
Similar To Industry Standard LT1086/LT1586
APPLICATIONS
•
Powering VGA & Sound Card
•
Power PCSupplies
•
SMPS Post-Regulator
•
High Efficiency “Green” Computer Systems
•
High Efficiency Linear Power Supplies
•
Portable Instrumentation
•
Constant Current Regulators
•
Adjustable Power Supplies
•
Battery charger
PRODUCT DESCRIPTION
The AS2815 is a low power 1.5A adjustable and fixed voltage regulators that are very easy to use. It requires only 2 external resistors
to set the output voltage for adjustable version. The AS2815 are designed for low voltage applications that offers lower dropout
voltage and faster transient response. This device is an excellent choice for use in powering low voltage microprocessor that require a
lower dropout, faster transient response to regulate from +2.5V to 3.8V supplies and as a post regulator for switching supplies
applications. The AS2815 features low dropout of a maximum 1.2V.
The AS2815 offers over current limit and protection against over-current faults, reversed input polarity, reversed load insertion, and
positive and negative transient voltage. The I
Q
of this device flows into the load, which increases efficiency.
The AS2815 are offered in a 3-pin TO-220, TO-263 & TO-252 packages compatible with other 3 terminal regulators. For a 3A low
dropout regulator refer to the AS2830 data sheet.
ORDERING INFORMATION
TO-220
3-PIN
AS2815YU-X
DD PLASTIC
3-PIN
AS2815YT-X
TO-252
DPAK
AS2815YR-X
OPERERATING JUNCTION
TEMP RANGE
-45 to +125°C
X = Output Voltage (i.e. 1.5 for 1.5V, 2.5 for 2.5V etc.).
Y = Output Tolerance, Y= A for 1% or
Blank for 2%
Consult with factory for other fixed output voltages
PIN CONNECTIONS
TO-263-3 (T)
TO-220-3 (U)
TO-252 (R)
AS2815
1
2
3
AS2815
1
2
3
1
AS2815
2
3
ADJ/GND V
OUT
V
IN
ADJ/GND V
OUT
V
IN
Front View
Top View
ADJ/GND V
OUT
V
IN
Front View
Rev. 10/11/00
AS2815
ABSOLUTE MAXIMUM RATINGS
Lead Temp. (Soldering, 10 Seconds) .............................. 300°C
Storage Temperature Range ............................ -65° to +150°C
Operating Junction Temperature Range ......................
AS2815 Control Section ............................ -45°C +125°C
AS2815 Power Transistor...........................-45°C +150°C
Maximum Input Supply Voltage .......................... 10V
Input to Output Voltage Differential .................... 10V
ELECTRICAL CHARACTERISTICS
(NOTE 1) at I
OUT
= 10mA, T
a
=25°C, unless otherwise specified.
AS2815A
PARAMETER
CONDITIONS
Typ
Min
Max
1.515
1.530
2.525
2.550
3.330
3.360
5.05
5.10
AS2815
Min
Max
1.470
1.455
1.530
1.545
Units
V
1.5V Version
Output Voltage (Note 2)
2.5V Version
Output Voltage (Note 2)
3.3V Version
Output Voltage (Note 2)
5.0V Version
Output Voltage (Note 2)
All Voltage Options
Reference Voltage (V
REF
)
Min. Load Current
(Note 3)
Line Regulation (∆V
REF
(V
IN
))
AS2815-1.5V, 0
≤I
OUT
≤1.5A,
2.75V≤V
IN
≤7V
1.5
1.5
2.5
2.5
3.3
3.3
5.0
5.0
1.485
1.470
2.475
2.450
3.270
3.240
4.95
4.90
AS2815-2.5V,0
≤I
OUT
≤1.5A,
3.5V≤V
IN
≤7V
2.450
2.425
3.230
3.201
4.900
4.850
2.550
2.575
3.370
3.399
5.100
5.150
V
AS2815-3.3V, 0
≤I
OUT
≤1.5A,
4.75V≤V
IN
≤7V
V
AS2815-5.0V, 0
≤I
OUT
≤1.5A,
5.5V≤V
IN
≤7V
V
V
IN
≤
7V, P≤ P
MAX
1.5V≤ (V
IN -
V
OUT
)≤5.75V, 10mA≤I
OUT
≤1.5A
1.5V≤ (V
IN -
V
OUT
)≤5.75V
2.75V≤V
IN
≤7V,
I
OUT
=10mA, T
J
=25°C (Note 3)
V
IN
≤7V,
I
OUT
=0mA, T
J
=25°C (Note 2)
V
1.250
5
0.005
0.005
0.05
1.225
1.270
10
0.2
0.2
0.3
1.225
1.270
10
0.2
0.2
0.3
mA
%
%
%
Load Regulation(∆V
REF
(I
OUT
))
10mA≤I
OUT
≤1.5A,
(V
IN
-V
OUT
)=3V, T
J
=25°C
(Note 3)
0≤I
OUT
≤1.5A,
V
IN
=7V, T
J
=25°C (Note 2)
0.05
1.1
0.3
1.2
0.3
1.2
%
V
A
Dropout Voltage
Current Limit
I
OUT
(
MAX
)
Long Term Stability
Thermal Regulation
(∆V
OUT
(Pwr))
Temperature Stability
(∆V
OUT
(T))
Output Noise, RMS
Thermal Resistance
∆V
REF
=1%
I
OUT
=1.5A (Note 3)
I
OUT
≤
1.5A (Note 2)
V
IN
=7V
1.4V≤ (V
IN
- V
OUT
) (Note3)
T
A
=125°C, 1000 Hrs.
T
A
=25°C, 20 ms pulse
2.5
0.3
(Note 2)
0.01
0.25
1.7
1
0.020
1.7
1
0.020
%
%/W
%
% V
O
3.0
60
3.0
60
3.0
60
3.0
60
°C/W
°C/W
10Hz to 10khz
TO-220
DD Package
T
A
=25°C
Junction to Tab
Junction to Ambient
Junction to Tab
Junction to Ambient
0.003
The Bold specifications apply to the full operating temperature range.
Note 1: Changes in output voltage due to heating effects are covered under the specification for thermal regulation.
Note 2: Fixed Version Only
Note 3: Adjustable Version Only
Rev. 10/11/00
AS2815
APPLICATION HINTS
The AS2815 incorporates protection against over-current
faults, reversed load insertion, over temperature operation, and
positive and negative transient voltage. However, the use of
an output capacitor is required in order to insure the stability
and the performances.
Stability
The output capacitor is part of the regulator’s frequency
compensation system. Either a 22µF aluminum electrolytic
capacitor or a 10µF solid tantalum capacitor between the
output terminal and ground guarantees stable operation for all
operating conditions.
However, in order to minimize overshoot and undershoot, and
therefore optimize the design, please refer to the section
‘Ripple Rejection’.
Ripple Rejection
Ripple rejection can be improved by adding a capacitor
between the ADJ pin and ground. When ADJ pin bypassing is
used, the value of the output capacitor required increases to its
maximum (22µF for an aluminum electrolytic capacitor, or
10µF for a solid tantalum capacitor). If the ADJ pin is not
bypass, the value of the output capacitor can be lowered to
100µF for an electrolytic aluminum capacitor or 4.7µF for a
solid tantalum capacitor.
However the value of the ADJ-bypass capacitor should be
chosen with respect to the following equation:
C = 1 / ( 6.28 * F
R
* R
1
)
Where C
= value of the capacitor in Farads (select an
equal or larger standard value),
F
R
= ripple frequency in Hz,
R
1
= value of resistor R
1
in Ohms.
If an ADJ-bypass capacitor is use, the amplitude of the output
ripple will be independent of the output voltage. If an ADJ-
bypass capacitor is not used, the output ripple will be
proportional to the ratio of the output voltage to the reference
voltage:
M = V
OUT
/ V
REF
Where M = multiplier for the ripple seen when the ADJ pin
is optimally bypassed.
V
REF
= Reference Voltage
Reducing parasitic resistance and inductance
One solution to minimize parasitic resistance and inductance is
to connect in parallel capacitors. This arrangement will
improve the transient response of the power supply if your
system requires rapidly changing current load condition.
Thermal Consideration
Although the AS2815 offers some limiting circuitry for
overload conditions, it is necessary not to exceed the
maximum junction temperature, and therefore to be careful
about thermal resistance. The heat flow will follow the lowest
resistance path, which is the Junction-to-case thermal
resistance. In order to insure the best thermal flow of the
component, a proper mounting is required. Note that the case
of the device is electrically connected to the output. In case
the case has to be electrically isolated, a thermally conductive
spacer can be used. However do not forget to consider its
contribution to thermal resistance.
Assuming:
V
IN
= 10V, V
OUT
= 5V, I
OUT
= 1.5A, T
A
= 50°C/W,
θ
Heatsink Case
= 6°C/W,
θ
Heatsink Case
= 0.5°C/W,
θ
JC
= 3°C/W
Power dissipation under this condition
P
D
= (V
IN
– V
OUT
) * I
OUT
= 7.5W
Junction Temperature
T
J
= T
A
+ P
D
* (θ
Case – HS
+
θ
HS
+
θ
JC
)
For Control & Power Sections
T
J
= 50 + 7.5*(0.5+6=3) = 121.25°C
121.25°C < T
J (max)
for Control & Power Sections.
In both case reliable operation is insured by adequate junction
temperature.
Rev. 10/11/00
AS2815
Basic Adjustable Regulator
V
OUT
AS2815
V
REF
I
ADJ
V
OUT
R
1
V
IN
5V
AS2815
C1
10uF
V
OUT
3.3V
C1
10uF
50µA
R
2
V
OUT
= V
REF
* ( 1 + R /R
1
) + I
ADJ
* R
2
2
Basic Fixed Regulator
Fig.2 Basic Adjustable Regulator
Output Voltage
Consider Figure 2. The resistance R
1
generates a constant
current flow, normally the specified load current of 10mA.
This current will go through the resistance R
2
to set the overall
output voltage. The current I
ADJ
is very small and constant.
Therefore its contribution to the overall output voltage is very
small and can generally be ignored.
Load Regulation
Parasitic line resistance can degrade load regulation. In order
not to affect the behavior of the regulator, it is best to connect
directly the R
1
resistance from the resistor divider to the case,
and not to the load. For the same reason, it is best to connect
the resistor R
2
to the Negative side of the load.
R
P
Parasitic Line
Resistance
Output Voltage
The fixed voltage LDO voltage regulators are simple to use
regulators since the V
OUT
is preset to the specifications. It is
important however, to provide the proper output capacitance
for stability and improvement. For most operating conditions
a capacitance of 22uF tantalum or 100uF electrolytic will
ensure stability and prevent oscillation.
V
OUT
AS2815
Connect R
1
to
Case of Regulator
R
1
R
L
R
2
Connect R
2
to Load
Fig.3 Basic Adjustable Regulator
Rev.10/11/00
AS2815
TYPICAL APPLICATIONS
V
IN
C
1
IN
AS2815
ADJ
V
IN
OUT
C
1
IN
AS2815
ADJ
OUT
C
2
R
1
V
OUT
R
1
LOAD
V
OUT
= V
REF
(1 + R
2
) + I
ADJ
R
2
R
1
R
2
Fig. 4 1.5A Current output Regulator
Fig. 5 Typical Adjustable Regulator
(Note A)
V
IN
IN
5V
+
10µF
AS2815
ADJ
OUT
V
OUT
R
1
121Ω
1%
150µF
V
IN
(Note A)
+
IN
AS2815
ADJ
OUT
5V
121Ω
1%
+
100µF
10µF
1k
2N3904
1k
365Ω
1%
*C
1
improves ripple rejection. Xc
should be ~ R
1
at ripple frequency.
R
2
365Ω
1%
TTL
Input
+
C
1
10µF*
Note A: V
IN(MIN)
= (Intended V
OUT
) + (V
DROPOUT (MAX)
)
Note A: V
IN(MIN)
= (Intended V ) + (V
DROPOUT (MAX)
)
OUT
Fig. 6
Improving Ripple Rejection
Fig.7 5V Regulator with Shutdown
Rev. 10/11/00
51单片机
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