Datasheet AS2850YU-5.0, AS2850YU-3.3, AS2850U-2.5, AS2850U-1.5, AS2850U Datasheet (Sipex)

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 PCSupplies

•

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) ..............................300°C Input Voltage........................................................ 10V

Storage Temperature Range ............................ -65° to +150°C Input to Output Voltage Differential .................... 10V

Operating Junction Temperature Range

AS2850 Control Section............................ -45°C +125°C

AS2850 Power Transistor...........................-45°C +150°C

ELECTRICAL CHARACTERISTICS

(NOTE 1)

at I

OUT

= 10mA, TA=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<VIN<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<VIN<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<VIN<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, 6.5V≤V

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, 10mA≤I

OUT

≤

5A

Min. Load Current (Note 3)

1.5V≤ (V

IN

–V

OUT

)≤5.75V

5 10 10

V

Line Regulation (∆Vref(Vin)) 2.75V≤VIN ≤7V, Iout=10mA, TJ=25ºC

(Note 3)

0.005 0.2 0.2

V

IN

≤7V, I

OUT

=0mA, TJ=25ºC (Note 2)

0.005 0.2 0.2

%

10mA≤I

OUT

≤5A, (VIN-V

OUT

)=3V, TJ=25ºC (Note 3)

0.05 0.3 0.3

Load Regulation(∆Vref(Iout))

0≤I

OUT

≤5A, VIN=7V, TJ=25ºC (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

VIN=7V 6 5.2 5.2 A Current Limit

Iout(MAX)

1.4V ≤ (V

IN

- V

OUT

) (Note3)

Long Term Stability TA=125ºC, 1000 Hrs. 0.3

(Note 2)

1 1 %

Thermal Regulation
(∆Vout(Pwr))

TA=25ºC, 20 ms pulse 0.01 0.020 0.020 %/W

Temperature Stability
(∆Vout(T))

0.25 %

Output Noise, RMS 10Hz to 10kHz TA=25ºC 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

ºC/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 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 (220µF for an aluminum electrolytic capacitor, or
47µF 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

* R1 )

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 R1 in Ohms.

If an ADJ-bypass capacitor is use, the amplitude of the output
ripple will be independent of the output voltage. If an ADJ­bypass 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, TA = 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

= (VIN – V

OUT

) * I

OUT

= 7.5W

Junction Temperature
T

J

= TA + PD * (

θ

Case – HS

+ θ

HS

θ

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 + R2/R1) + 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 R2 to Load

R

L

Connect R1 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 + R2 ) + I

ADJ R2

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

150µF

10µF*

121Ω

1%

365Ω

1%

+

+

10µF

C

1

*C1 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

100µF

121Ω

1%

365Ω

1%

+

+

10µF

5V

ADJ

IN OUT

(Note A)

1k

1k

TTL

Input

2N3904

Note A: V

IN(MIN)

= (Intended V

OUT

) + (V

DROPOUT (MAX)

)

Rev. 10/11/00

AS2850

TYPICAL CHARACTERISTICS