ETC AS2887AR

AS2887
3A Low Dropout Voltage Regulator
Adjustable & Fixed Output,
Fast Response
FEATURES
APPLICATIONS
• 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
• 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 AS2887 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 AS2887 is designed for low voltage applications that offer 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 AS2887 features low dropout of a maximum of 1.5 volts.
The AS2887 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 IQ of this device flows into load which
increases efficiency.
The AS2887 are offered in a 3-pin TO-220, TO-263 & TO-252 packages compatible with other 3 terminal regulators. For a 8A low
dropout regulator refer to the AS2880 data sheet.
ORDERING INFORMATION
TO-220
3-PIN
AS2887YU
AS2887YU-X
DD PLASTIC
3-PIN
AS2887YT
AS2887YT-X
TO-252
DPAK
AS2887YR
AS2887YR-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 with factory for other fixed output voltages
PIN CONNECTIONS
TO-263-3 (T)
TO-220-3 (U)
AS2887
1
2
TO-252 (R)
AS2887
3
AS2887
1
2
1
2
3
3
ADJ/GND VOUT VIN
Front View
ADJ/GND VOUT VIN
Top View
ADJ/GND VOUT VIN
Front View
Rev. 10/11/00
AS2887
ABSOLUTE MAXIMUM RATINGS
Lead Temp. (Soldering, 10 Seconds) .............................. 300°C
Storage Temperature Range ............................ -65° to +150°C
Operating Junction Temperature Range ......................
AS2887 Control Section ............................ -45°C +125°C
AS2887 Power Transistor...........................-45°C +150°C
Input Voltage........................................................ 30V
Input to Output Voltage Differential Max ............ 30V
ELECTRICAL CHARACTERISTICS (NOTE 1) at IOUT = 10mA, TA=25°C, unless otherwise specified.
AS2887A
PARAMETER
CONDITIONS
Typ
Min
Max
AS2887
Min
Max
Units
1.5V Version
Output Voltage (Note 2)
AS2887-1.5V, 0 ≤IOUT≤3A, 2.75V≤VIN ≤29V
1.5
1.5
1.485
1.470
1.515
1.530
1.470
1.455
1.530
1.545
V
2.5V Version
Output Voltage (Note 2)
AS2887-2.5V,0 ≤IOUT≤3A, 3.5V≤VIN ≤29V
2.5
2.5
2.475
2.450
2.525
2.550
2.450
2.425
2.550
2.575
V
3.3V Version
Output Voltage (Note 2)
AS2887-3.3V, 0 ≤IOUT≤3A, 4.75V≤VIN ≤29V
3.3
3.3
3.270
3.240
3.330
3.360
3.230
3.201
3.370
3.399
V
5.0V Version
Output Voltage (Note 2)
AS2887-5.0V, 0 ≤IOUT≤3A, 5.5V≤VIN ≤29V
5.0
5.0
4.95
4.90
5.05
5.10
4.900
4.850
5.100
5.150
V
1.250
1.238
1.263
1.225
1.270
V
Adjustable Version
Reference Voltage (VREF)
All Voltage Options
Min. Load Current (Note 3)
Line Regulation (∆VREF(VIN))
VIN≤ 7V, P≤ PMAX
1.5V≤ (VIN -VOUT)≤(VIN-VOUT)MAX,
10mA≤IOUT≤3A
5
10
10
mA
2.75V≤VIN ≤29V, IOUT=10mA, TJ=25°C (Note 3)
0.005
0.2
0.2
%
VIN ≤29V, IOUT=0mA, TJ=25°C (Note 2)
0.005
0.2
0.2
%
10mA≤IOUT ≤3A, (VIN-VOUT)=3V, TJ=25°C (Note
3)
0.05
0.3
0.3
%
0≤IOUT ≤3A, VIN=7V, TJ=25°C (Note 2)
0.05
0.3
0.3
%
Dropout Voltage
∆VREF=1%
1.1
1.5
1.5
V
Current Limit
IOUT(MAX)
Long Term Stability
VIN=7V
1.4V≤ (VIN- VOUT) (Note3)
TA=125°C, 1000 Hrs.
0.3
(Note 2)
1
1
%
Thermal Regulation
(∆VOUT(Pwr))
Temperature Stability
(∆VOUT(T))
Output Noise, RMS
Thermal Resistance
TA=25°C, 20 ms pulse
0.01
0.020
0.020
%/W
Load Regulation(∆VREF(IOUT))
1.5V≤ (VIN -VOUT)≤ (VIN-VOUT)MAX
IOUT =3A (Note 3)
IOUT≤ 3A (Note 2)
A
4.0
3.2
3.2
0.25
10Hz to 10kHz
TO-220
DD Package
TA=25°C
Junction to Tab
Junction to Ambient
Junction to Tab
Junction to Ambient
%
0.003
3.0
60
3.0
60
% VO
3.0
60
3.0
60
3.0
60
3.0
60
°C/W
°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
AS2887
APPLICATION HINTS
The AS2887 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.
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 220µF aluminum electrolytic
capacitor or a 47µF 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 AS2887 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.
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
100µF for an electrolytic aluminum capacitor or 15µF 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 * FR * R1 )
Where C
= value of the capacitor in Farads (select an
equal or larger standard value),
FR = ripple frequency in Hz,
R1 = 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 = VOUT / VREF
Where M = multiplier for the ripple seen when the ADJ pin
is optimally bypassed.
VREF = Reference Voltage
Assuming:
VIN = 10V, VOUT = 5V, IOUT = 1.5A, TA = 50°C
θ Heatsink = 6°C/W, θ Case-Heatsink = 0.5°C/W, θ JC = 3°C/W
Power dissipation under this condition
PD = (VIN – VOUT) * IOUT = 7.5W
Junction Temperature
TJ = TA + PD * (θCase – HS + θ HS + θ JC)
For the Control Sections
TJ = 50 + 7.5*(0.5 +6=3) = 121.25°C
121.25°C < TJ(max) for the control section.
In both case reliable operation is insured by adequate junction
temperature.
Rev. 10/11/00
AS2887
Basic Adjustable Regulator
VIN
VOUT
AS2887
VREF
R1
IADJ
50µA
R2
VOUT = VREF * ( 1 + R2/R1) + IADJ * R2
Fig.2 Basic Adjustable Regulator
Output Voltage
Consider Figure 2. The resistance R1 generates a constant current flow, normally the specified load current of 10mA. This current will
go through the resistance R2 to set the overall output voltage. The current IADJ 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 R1 resistance from the resistor divider to the case, and not to the load. For the same reason, it is best to connect the resistor R2 to
the Negative side of the load.
VIN
R P Parasitic Line
Resistance
AS2887
Connect R 1 to
Case of Regulator
R1
RL
R2
Connect R 2 to Load
Fig.3 Basic Adjustable Regulator
Rev. 10/11/00
AS2887
TYPICAL APPLICATIONS
VIN
IN
AS2887
VIN
OUT
C2
Fig. 5 Typical Adjustable Regulator
Fig. 4 3A Current output Regulator
IN
AS2887
+
10µF
5V
*C 1 improves ripple rejection. Xc
should be ~ R 1 at ripple frequency.
VOUT
OUT
ADJ
R2
VOUT = VREF (1 + R2 ) + IADJ R2
R1
LOAD
(Note A)
R1
ADJ
R1
ADJ
VOUT
OUT
C1
C1
VIN
AS2887
IN
VIN
+
150µF
+
C1
10µF*
AS2887
5V
OUT
121Ω
1%
ADJ
R1
121Ω
1%
R2
365Ω
1%
IN
(Note A)
TTL
Input
+
10µF
100µF
1k
2N3904
1k
365Ω
1%
Note A: VIN(MIN) = (Intended VOUT) + (VDROPOUT (MAX))
Note A: VIN(MIN)= (Intended VOUT) + (VDROPOUT (MAX))
Fig. 6
Improving Ripple Rejection
Fig.7 5V Regulator with Shutdown
Rev. 10/11/00
AS2887
TYPICAL CHARACTERISTICS
Rev. 10/11/00