AP1084
5A Low Dropout Positive Adjustable or Fixed-Mode Regulator
Features
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General Description
AP1084 is a low dropout positive adjustable or fixed-
mode regulator with minimum of 5.0A output current
capability. The product is specifically designed to
provide well-regulated supply for low voltage IC
applications such as high-speed bus termination and
low current 3.3V logic supply. AP1084 is also well
suited for other applications such as VGA cards.
AP1084 is guaranteed to have lower than 1.4V
dropout at full load current making it ideal to provide
well-regulated outputs of 1.25 to 3.3V with 4.7 to
12V input supply.
1.4V maximum dropout at full load current
Built-in thermal shutdown
Output current limiting
Adjustable output voltage or fixed 1.5V, 1.8V, 2.5V,
3.3V, 5.0V
Fast transient response
Good noise rejection
Package: TO252, TO263, TO220, PDIP-8
Ordering Information
AP1084 X
X
X
X
Low Dropout Regulator
Package
D : TO252-3L
K : TO263-3L
T : TO220-3L
N : PDIP-8L
Vout
Blank : Adj
15 = 1.5V
18 = 1.8V
25 = 2.5V
33 = 3.3V
50 = 5.0V
Lead Free
Packing
Blank : Normal
Blank : Tube
L : Lead Free Package A : Taping
Block Diagram
Vin
3
2 Vout
+
+
－
1.25V
CURRENT
LIMIT
+
Thermal
Shutdown
1
Adj
－
+
This datasheet contains new product information. Anachip Corp. reserves the rights to modify the product specification without notice. No liability is assumed as a result of the use of
this product. No rights under any patent accompany the sale of the product.
Rev.1.2 Jun.9, 2005
1/11
AP1084
5A Low Dropout Positive Adjustable or Fixed-Mode Regulator
Absolute Maximum Ratings
Symbol
Vin
P
D
T
ST
T
OP
Parameter
DC Supply Voltage
Power Dissipation
Storage Temperature
Operating Junction Temperature Range
Rating
Unit
-0.3 to 12
V
Internally Limited
oC
-65 to +150
oC
0 to +150
Electrical Characteristics
Sym.
V
REF
(Under Operating Conditions)
Min.
1.225
1.470
1.764
2.450
3.235
4.900
Parameter
Conditions (Notes)
Io=10mA, Tj=25
o
C, (Vin-Vout)=1.5V
I
O
=10mA, V
OUT
+1.5V<V
IN
<12V, T
J
=25
o
C
I
OUT
= 10mA, T
J
= 25
o
C, 3V≦V
IN
≦12V
I
OUT
= 10mA, T
J
= 25
o
C, 3.3V≦V
IN
≦12V
I
OUT
= 10mA, T
J
= 25
o
C, 4V≦V
IN
≦12V
I
OUT
= 10mA, T
J
= 25
o
C, 4.8V≦V
IN
≦12V
I
OUT
= 10mA, T
J
= 25
o
C, 6.5V≦V
IN
≦12V
V
IN
=3.3V, 0mA<Io<5A, T
J
=25
o
C
(Note 1,2)
V
IN
=3V, 0mA<Io<5A, T
J
=25
o
C
(Note 1,2)
V
IN
=3.3V, 0mA<Io<5A
T
J
=25
o
C (Note 1,2)
V
IN
=4V, 0mA<Io<5A
T
J
=25
o
C (Note 1,2)
V
IN
= 5V, 0mA<Io<5A , T
J
=25
o
C (Note 1,2)
V
IN
= 8V, 0mA<Io<5A, T
J
=25
o
C (Note 1,2)
Io=5.0A (∆Vout = 1% Vout)
Vin-Vout=5V
Typ.
1.250
1.500
1.800
2.500
3.300
5.000
Max.
1.275
0.2
1.530
1.836
2.550
3.365
5.100
1
Unit
V
%
V
V
V
V
V
%
mV
mV
mV
mV
mV
V
A
mA
%
Reference Voltage
AP1084-XXX
AP1084-1.5
AP1084-1.8
Line
Regulation AP1084-2.5
AP1084-3.3
AP1084-5.0
AP1084-Adj
AP1084-1.5
Load
AP1084-1.8
Regulation
AP1084-2.5
AP1084-3.3
AP1084-5.0
Dropout Voltage
Current Limit
Minimum Load
Current
Temperature
Stability
Thermal Resistance
Junction-to-Ambient
(No heat sink ;No
air flow)
Thermal Resistance
Junction-to-Ambient
12
15
20
26
40
1.3
5.1
5
15
18
25
33
50
1.4
10
∆Vo
Io=10mA
TO-252
TO-263
TO-220
0.5
98
83
83
35
10
0.65/2.7
0.65/2.7
O
θ
JA
O
C/W
θ
JC
PDIP-8: Control Circuitry/Power Transistor
(Note 3)
TO-252: Control Circuitry/Power Transistor
Thermal Resistance
TO-263: Control Circuitry/Power Transistor
Junction-to-Case
TO-220: Control Circuitry/Power Transistor
C/W
Note 1:
See thermal regulation specifications for changes in output voltage due to heating effects. Line and load regulation are measured
at a constant junction temperature by low duty cycle pulse testing. Load regulation is measured at the output lead = 1/18” from the
package.
Note 2:
Line and load regulation are guaranteed up to the maximum power dissipation of 15W. Power dissipation is determined by the
difference between input and output and the output current. Guaranteed maximum power dissipation will not be available over the
full input/output range.
Note 3:
Output is connected to the PCB cupper area 5.5mm*5.5mm separately. If you need large PD or lower Tc & Tj, please connect to
the large cupper area >> 5.5mm*5.5mm (like 10mm*10mm).
Anachip Corp.
www.anachip.com.tw
3/11
Rev.1.2
Jun.9, 2005
AP1084
5A Low Dropout Positive Adjustable or Fixed-Mode Regulator
Functional Description
Introduction
The AP1084 adjustable Low Dropout (LDO) regulator
is a 3 terminal device that can easily be programmed
with the addition of two external resistors to any
voltages within the range of 1.25V to Vin-1.4V. The
AP1084 only needs 1.4V differential between Vin and
Vout to maintain output regulation. In addition, the
output voltage tolerances are also extremely tight and
they include the transient response as part of the
specification. For example, Intel VRE specification
calls for a total of +/- 100mV including initial tolerance,
load regulation and 0 to 5.0A load step.
The AP1084 is specifically designed to meet the fast
current transient needs as well as providing an
accurate initial voltage, reducing the overall system
cost with the need for fewer output capacitors.
Output Voltage Setting
The AP1084 can be programmed to any voltages in
the range of 1.25V to Vin-1.4V with the addition of R1
and R2 external resistors according to the following
formula:
Vout = Vref (1+ R2/R1) +Iadj *R2 , where Vref = 1.25 typically, Iadj =
55uA typically R1&R2 as shown at below
Vin
AP1084
Adj
Vout
Vref
R1
Iadj=55uA
R2
The AP1084 keeps a constant 1.25V between the
output pin and the adjust pin. By placing a resistor R1
across these two pins a constant current flows through
R1, adding to the
Iadj
current and into the R2 resistor
producing a voltage equal to the (1.25/R1)*R2+Iadj*R2
which will be added to the 1.25V to set the output
voltage. This is summarized in the above equation.
Since the minimum load current requirement of the
AP1084 is 10mA, R1 is typically selected to be 121Ω
resistor so that it automatically satisfies the minimum
current requirement. Notice that since Iadj is typically
in the range of 55uA it only adds a small error to the
output voltage and should only be considered when a
very precise output voltage setting is required. For
example, in a typical 3.3V application where R1=121Ω
and R2=200Ω the error due to
Iadj
is only 0.3% of the
nominal set point.
Load Regulation
Since the AP1084 is only a 3 terminal device, it is not
possible to provide true remote sensing of the output
voltage at the load. The best load regulation is
achieved when the bottom side of R2 is connected to
the load and the top-side of R1 resistor is connected
directly to the case or the Vout pin of the regulator and
not to the load. It is important to note that for high
current applications, this can re-present a significant
percentage of the overall load regulation and one must
keep the path from the regulator to the load as short
as possible to minimize this effect.
Stability
The AP1084 requires the use of an output capacitor as
part of the frequency compensation in order to make
the regulator stable. For most applications a minimum
of 10uF aluminum electrolytic capacitor insures both
stability and good transient response.
Thermal Design
The AP1084 incorporates an internal thermal
shutdown that protects the device when the junction
temperature exceeds the maximum allowable junction
temperature. Although this device can operate with
junction temperatures in the range of
150
o
C,
it is
recommended that the selected heat sink be chosen
such that during maximum continuous load operation
the junction temperature is kept below the temperature.
Layout Consideration
The output capacitors must be located as close to the
Vout terminal of the device as possible. It is
recommended to use a section of a layer of the PC
board as a plane to connect the Vout pin to the output
capacitors to prevent any high frequency oscillation
that may result due to excessive trace inductance.
Anachip Corp.
www.anachip.com.tw
5/11
Rev.1.2
Jun.9, 2005
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