α
FEATURES
ALPHA
SEMICONDUCTOR
Excellence in Analog Power Products
AS2830
3A Low Dropout Voltage Regulator
Adjustable & Fixed Output,
Fast Response
•
Adjustable Output Down To 1.2V
•
Fixed Output Voltages 1.5, 2.5, 3.3, 5.0V
•
Output Current Of 3A
•
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 LT1085/LT1585
APPLICATIONS
•
Powering VGA & Sound Card
•
Power PC™Supplies
•
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 ALPHA Semiconductor AS2830 are low power 3A 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 AS2830 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 AS2830 features low dropout of a maximum 1.2 volts.
The AS2830 offers over current limit and full protection against reversed input polarity, reversed load insertion, and positive and
negative transient voltage. On-Chip trimming adjusts the reference voltage to 1%. The I
Q
of this device flows into the load, which
increases efficiency.
The AS2830 are offered in a 3-pin TO-220, TO-263 & TO-252 packages compatible with other 3 terminal regulators. For a 5A low
dropout regulator refer to the AS2850 data sheet.
ORDERING INFORMATION
TO-220
3-PIN
AS2830YU-X
DD PLASTIC
3-PIN
AS2830YT-X
TO-252
DPAK
AS2830YR-X
X = Output Voltage (i.e. 1.5 for 1.5V, 2.5 for 2.5V etc.)
Y= Output Tolerance, Y= A for 1%
Blank for 2%
Consult factory for other fixed voltages.
PIN CONNECTIONS
TO-263-3 (T)
ALPHA
AS2830
1
2
3
TO-220-3 (U)
TO-252 (R)
ALPHA
AS2830
1
2
3
ALPHA
AS2830
1
2
3
ADJ/GND
V
OUT
V
IN
ADJ/GND
V
OUT
V
IN
ADJ/GND V
OUT
V
IN
Front View
Top View
Front View
Alpha Semiconductor Inc. 1031 Serpentine Lane. Pleasanton, CA 94566 Tel: (9250 417-1391 Fax: (925) 417-1390
Rev.8/10/99
AS2830
ABSOLUTE MAXIMUM RATINGS
Lead Temp. (Soldering, 10 Seconds) ............................ 300°C
Storage Temperature Range .......................... -65° to +150°C
Operating Junction Temperature Range....................
AS2830 Control Section .......................... -45°C +125°C
AS2830 Power Transistor.........................-45°C +150°C
Maximum Input Voltage .................................... 10V
Input to Output Voltage Differential Max.......... 8.8V
ELECTRICAL CHARACTERISTICS
(NOTE 1) at I
OUT
= 10mA, T
a
=25°C, unless otherwise specified.
AS2830A
AS2830
PARAMETER
CONDITIONS
Typ
Min
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
)
AS2830-1.5V, 0
≤I
OUT
≤3A,
2.75V≤V
IN
≤10V
AS2830-2.5V,0
≤I
OUT
≤3A,
4.0V≤V
IN
≤10V
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
1.238
1.225
Units
V
Max
1.515
1.530
2.525
2.550
3.330
3.360
5.05
5.10
1.263
1.270
10
0.2
0.2
0.3
0.3
1.2
Min
1.470
1.455
2.450
2.425
3.230
3.201
4.900
4.850
1.225
1.212
Max
1.530
1.545
2.550
2.575
3.370
3.399
5.100
5.150
1.270
1.288
10
0.2
0.2
0.3
0.3
1.2
V
AS2830-3.3V, 0
≤I
OUT
≤3A,
4.75V≤V
IN
≤10V
AS2830-5.0V, 0
≤I
OUT
≤3A,
6.5V≤V
IN
≤10V
V
IN
≤
7V, P≤ P
MAX
1.5V≤ (V
IN -
V
OUT
)≤(V
IN
-V
OUT
)
MAX
,
10mA≤I
OUT
≤3A
1.5V≤ (V
IN -
V
OUT
)≤ (V
IN
-V
OUT
)
MAX
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)
10mA≤I
OUT
≤3A,
(V
IN
-V
OUT
)=3V, T
J
=25°C
(Note 3)
0≤I
OUT
≤3A,
V
IN
=7V, T
J
=25°C (Note 2)
∆V
REF
=1%
I
OUT
=3A
I
OUT
≤
3A
V
V
V
1.250
5
0.005
0.005
0.05
0.05
1.1
Min. Load Current (Note 3)
Line Regulation (∆V
REF
(V
IN
))
mA
%
%
%
%
V
A
Load Regulation(∆V
REF
(I
OUT
))
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
IN
=7V
1.4V≤ (V
IN
- V
OUT
) (Note3)
T
A
=125°C, 1000 Hrs.
T
A
=25°C, 20 ms pulse
4.0
0.3
(Note 2)
0.01
0.25
3.2
1
0.020
3.2
1
0.020
%
%/W
%
%V
°C/W
10Hz to 10kHz T
A
= 25°c
TO-220
Junction to Tab
Junction to Ambient
DD Package
Junction to Tab
Junction to Ambient
0.003
3.0
60
3.0
60
3.0
60
3.0
60
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
Alpha Semiconductor Inc. 1031 Serpentine Lane. Pleasanton, CA 94566 Tel: (9250 417-1391 Fax: (925) 417-1390
Rev.8/10/99
AS2830
APPLICATION HINTS
The ALPHA Semiconductor AS2830incorporates 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 improve the stability and the performances.
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.
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’.
Thermal Consideration
Although the AS2830 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 the Control Sections
T
J
= 50 + 7.5*(0.5 +6=3) = 121.25°C
121.25°C < T
J (max)
for the Control & Power Sections.
In both case reliable operation is insured by adequate junction
temperature.
Ripple Rejection
Ripple rejection can be improved by adding a capacitor
between the ADJ pin and ground as shown in figure 6. 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 10µF 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
Alpha Semiconductor Inc. 1031 Serpentine Lane. Pleasanton, CA 94566 Tel: (9250 417-1391 Fax: (925) 417-1390
Rev.8/10/99
AS2830
Basic Adjustable Regulator
V
IN
ALPHA
AS2830
V
REF
I
ADJ
50µA
V
OUT
R
1
V
IN
5V
ALPHA
AS2830
C1
10uF
V
OUT
3.3V
C2
10uF
R
2
V
OUT
= V
REF
* ( 1 + R
2
/R
1
) + I
ADJ
* R
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
IN
ALPHA
AS2830
Connect R to
1
Case of Regulator
R
1
R
L
R
2
Connect R to Load
2
Fig.3 Basic Adjustable Regulator
Alpha Semiconductor Inc. 1031Serpentine Lane. Pleasanton, CA 94566 Tel: (925) 417-1391 Fax: (925) 417-1390
Rev. 8/10/99
AS2830
TYPICAL APPLICATIONS
V
IN
C
1
IN
ALPHA
AS2830
ADJ
V
IN
OUT
C
1
R
1
IN
ALPHA
AS2830
ADJ
OUT
R
1
C
2
V
OUT
LOAD
V
OUT
= V
REF
(1 + R
2
) + I
ADJ
R
2
R
1
R
2
Fig. 4 3A Current output Regulator
Fig. 5 Typical Adjustable Regulator
(Note A)
V
IN
+
10µF
IN
ALPHA
AS2830
ADJ
5V
OUT
V
OUT
R
1
121Ω
1%
150µF
V
IN
(Note A)
+
10µF
TTL
Input
1k
IN
ALPHA
OUT
AS2830
ADJ
5V
121Ω
1%
+
100µF
*C
1
improves ripple rejection. X
C
should be ~ R
1
at ripple frequency.
2N3904
1k
R
2
365Ω
1%
+
C
1
10µF*
365Ω
1%
Note A: V
IN(MIN)
= (Intended V
OUT
) + (V
DROPOUT (MAX)
)
Note A: V
IN(MIN)
= (Intended V
OUT
) + (V
DROPOUT (MAX)
)
Fig. 6
Improving Ripple Rejection
Fig.7 5V Regulator with Shutdown
Alpha Semiconductor Inc. 1031Serpentine Lane. Pleasanton, CA 94566 Tel: (925) 417-1391 Fax: (925) 417-1390
Rev. 8/10/99
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