Rev. 10/11/00
AS2850
5A Low Dropout Voltage Regulator
Adjustable & Fixed Output,
Fast Response
FEATURES
APPLICATIONS
Adjustable Output Down To 1.2V
Powering VGA & Sound Card
Fixed Output Voltages 1.5V, 2.5V, 3.3V & 5.0V
Power PCSupplies
Output Current Of 5A
SMPS Post-Regulator
Low Dropout Voltage 1.1V Typ @ 5A.
High Efficiency "Green" Computer Systems
Extremely Tight Load And Line Regulation
High Efficiency Linear Power Supplies
Current & Thermal Limiting
Portable Instrumentation
Standard 3-Terminal Low Cost TO-220 & TO-263
Constant Current Regulators
Similar To Industry Standard LT1085/LT1585
Adjustable Power Supplies
Battery charger
PRODUCT DESCRIPTION
The AS2850 are low power 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 AS2850 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 AS2850 features low dropout of a maximum 1.2 volts.
The AS2850 offers full protection against over-current faults, 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 AS2850 are offered in a 3-pin TO-220 and TO-263 package compatible with other 3 terminal regulators. For a 8A low dropout
regulator refer to the AS2880 data sheet.
ORDERING INFORMATION
TO-220
3-PIN
DD PLASTIC
3-PIN
AS2850YU-X AS2850YT-X
X= Output Voltage (i.e. 1.5 for 1.5V, 2.5 for 2.5V etc.)
Y= Output Tolerance, A for 1%
Blank for 2%
Consult factory for other fixed voltages.
PIN CONNECTIONS
Top View
TO-263-3 (T)
1
2
3
ADJ/GND
V
OUT
V
IN
AS2850
Front View
TO-220-3 (U)
AS2580
1
2
V
IN
V
OUT
ADJ/GND
3
Rev. 10/11/00
AS2850
ABSOLUTE MAXIMUM RATINGS
Lead Temp. (Soldering, 10 Seconds) .............................. 300C
Input Voltage........................................................ 10V
Storage Temperature Range ............................ -65 to +150C
Input to Output Voltage Differential .................... 10V
Operating Junction Temperature Range
AS2850 Control Section ............................ -45C +125C
AS2850 Power Transistor...........................-45C +150C
ELECTRICAL CHARACTERISTICS
(NOTE 1)
at I
OUT
= 10mA, T
A
=25
C, unless otherwise specified.
PARAMETER CONDITIONS
Typ
AS2850A
AS2850
UNITS
Min
Max
Min
Max
1.5V Version
1.485 1.515 1.47 1.53
V
Output Voltage (Note 2)
AS2850-1.5V, 0 < I
OUT
< 5A, 3.3V<V
IN
<10V 1.5
1.47 1.53 1.455 1.545
2.5V Version
2.475 2.525 2.45 2.55
V
Output Voltage (Note 2)
AS2850-2.5V, 0 < I
OUT
< 5A, 4.0V<V
IN
<10V 2.5
2.45 2.55 2.425 2.575
3.3V Version
3.267 3.333 3.234 3.366 V
Output Voltage (Note 2)
AS2850-3.3V, 0 < I
OUT
< 5A, 4.8V<V
IN
<10V 3.3
3.234 3.366 3.069 3.399
5.0V Version
5 4.950
5.050
4.9 5.1 V
Output Voltage (Note 2)
AS2850-5.0V, 0
I
OUT
5A, 6.5VV
IN
12V
4.900 5.100 4.65 5.15
All Voltage Options
Reference Voltage (Vref)
1.250 1.225 1.270 1.225 1.270 V
V
IN
7V, P P
MAX
1.5V
(V
IN
-V
OUT
)
5.75V, 10mAI
OUT
5A
Min. Load Current (Note 3)
1.5V
(V
IN
V
OUT
)
5.75V
5
10 10
V
Line Regulation (
Vref(Vin)) 2.75VV
IN
7V, Iout=10mA, T
J
=25C
(Note 3)
0.005 0.2 0.2
V
IN
7V, I
OUT
=0mA, T
J
=25C (Note 2)
0.005 0.2 0.2
%
10mA
I
OUT
5A, (V
IN
-V
OUT
)=3V, T
J
=25C (Note 3)
0.05 0.3 0.3
Load Regulation(
Vref(Iout))
0
I
OUT
5A, V
IN
=7V, T
J
=25C (Note 2)
0.05 0.3 0.3
%
Dropout Voltage
V
REF
=1% I
OUT
= 5A (Note 3)
I
OUT
< 5A (Note 2)
1.1 1.2 1.2
V
IN
=7V 6
5.2
5.2
A
Current Limit
Iout(MAX)
1.4V
(V
IN
- V
OUT
) (Note3)
Long Term Stability
T
A
=125C, 1000 Hrs.
0.3
(Note 2)
1 1 %
Thermal Regulation
(
Vout(Pwr))
T
A
=25C, 20 ms pulse
0.01
0.020
0.020
%/W
Temperature Stability
(
Vout(T))
0.25
%
Output Noise, RMS
10Hz to 10kHz T
A
=25C 0.003
%
Vo
3.0
3.0
TO-220
Junction to Tab
Junction to Ambient
60
60
3.0
3.0
Thermal Resistance
DD Package
Junction to Tab
Junction to Ambient
60
60
C/W
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
AS2850
APPLICATION HINTS
The AS2850 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 22
F aluminum electrolytic
capacitor or a 10
F 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 (220
F for an aluminum electrolytic capacitor, or
47
F for a solid tantalum capacitor). If the ADJ pin is not
bypass, the value of the output capacitor can be lowered to
10
F for an electrolytic aluminum capacitor or 4.7F 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 AS2850 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,
Heatsink Case
= 6
C/W,
Heatsink Case
= 0.5
C/W,
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
* (
Case HS
+
HS
JC
)
For the Control Section
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.
Rev. 10/11/00
AS2850
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.
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.
AS2850
Fig.2 Basic Adjustable Regulator
V
REF
R
1
R
2
V
OUT
= V
REF
* ( 1 + R
2
/R
1
) + I
ADJ
* R
2
I
ADJ
ADJ
V
IN
V
OUT
50uA
AS2850
Fig.3 Basic Adjustable Regulator
V
IN
R
2
R
1
Connect R
2
to Load
R
L
Connect R
1
to
Case of Regulator
R
P
Parasitic Line
Resistance
V
OUT
ADJ
AS2850
Basic Fixed Regulator
V
IN
V
OUT
5V
C1
10uF
C2
10uF
3.3V
Rev. 10/11/00
AS2850
TYPICAL APPLICATIONS
IN
OUT
ADJ
AS2850
C
1
R
1
V
OUT
Fig. 5 Typical Adjustable Regulator
V
IN
LOAD
ADJ
AS2850
Fig. 4 5A Current output Regulator
V
IN
C
1
OUT
IN
R
2
C
2
V
OUT
= V
REF
(1 + R
2
) + I
ADJ
R
2
R
1
R
1
Note A: V
IN(MIN)
= (Intended V
OUT
) + (V
DROPOUT (MAX)
)
AS2850
Fig. 6 Improving Ripple Rejection
V
IN
R
1
R
2
150F
10F*
121
1%
365
1%
+
+
10F
C
1
*C
1
improves ripple rejection. Xc
should be ~ R
1
at ripple frequency.
5V
ADJ
IN
OUT
(Note A)
V
OUT
AS2850
Fig.7 5V Regulator with Shutdown
V
IN
100F
121
1%
365
1%
+
+
10F
5V
ADJ
IN
OUT
(Note A)
1k
1k
TTL
Input
2N3904
Note A: V
IN(MIN)
= (Intended V
OUT
) + (V
DROPOUT (MAX)
)
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