IRU1015CDTR International Rectifier, IRU1015CDTR Datasheet - Page 4

• Manufacturer Part Number: IRU1015CDTR
• Description: IC REG ADJ LDO 1.5A D-PAK
• Manufacturer: International Rectifier

Specifications of IRU1015CDTR

• Regulator Topology: Positive Adjustable
• Voltage - Output: 2.5 ~ 3.3 V
• Voltage - Input: Up to 7V
• Voltage - Dropout (typical): 1.1V @ 1.5A
• Number Of Regulators: 1
• Current - Output: 1.5A
• Current - Limit (min): 1.6A
• Operating Temperature: 0°C ~ 150°C
• Mounting Type: Surface Mount
• Package / Case: TO-252-2, DPak (2 Leads + Tab), TO-252AA, SC-63
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

IRU1015
Output Voltage Setting
The IRU1015 can be programmed to any voltages in the
range of 1.25V to 5.5V with the addition of R1 and R2
external resistors according to the following formula:
The IRU1015 keeps a constant 1.25V between the out-
put pin and the adjust pin. By placing a resistor R1 across
these two pins a constant current flows through R1, add-
ing to the I
a voltage equal to the (1.25/R1)3R2 + I
will be added to the 1.25V to set the output voltage. This
is summarized in the above equation. Since the mini-
mum load current requirement of the IRU1015 is 10mA,
R1 is typically selected to be 121V resistor so that it
automatically satisfies the minimum current requirement.
Notice that since I
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 appli-
cation where R1=121V and R2=200V the error due to
I
Load Regulation
Since the IRU1015 is only a three-terminal device, it is
not possible to provide true remote sensing of the output
voltage at the load. Figure 4 shows that 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 V
regulator and not to the load. In fact, if R1 is connected
4
ADJ
V
I N
is only 0.3% of the nominal set point.
V
Where:
V
I
R1 and R2 as shown in Figure 3:
ADJ
Figure 3 - Typical application of the IRU1015
OUT
REF
= 50mA Typically
= 1.25V Typically
= V
for programming the output voltage.
ADJ
REF
current and into the R2 resistor producing
3 1+
V
IN
( )
ADJ
IRU1015
is typically in the range of 50mA it
R2
R1
Adj
+I
I
ADJ
V
ADJ
OUT
= 50uA
3R2
V
REF
ADJ
R 1
R 2
OUT
3R2 which
pin of the
V
O U T
www.irf.com
to the load side, the effective resistance between the
regulator and the load is gained up by the factor of (1+
R2/R1),or the effective resistance will be R
R2/R1). It is important to note that for high current appli-
cations, this can represent 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 IRU1015 requires the use of an output capacitor as
part of the frequency compensation in order to make the
regulator stable. Typical designs for microprocessor ap-
plications use standard electrolytic capacitors with a
typical ESR in the range of 50 to 100mV and an output
capacitance of 500 to 1000mF. Fortunately as the ca-
pacitance increases, the ESR decreases resulting in a
fixed RC time constant. The IRU1015 takes advantage
of this phenomena in making the overall regulator loop
stable. For most applications a minimum of 100mF alu-
minum electrolytic capacitor such as Sanyo MVGX se-
ries, Panasonic FA series as well as the Nichicon PL
series insures both stability and good transient response.
Thermal Design
The IRU1015 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 tempera-
tures in the range of 1508C, it is recommended that the
selected heat sink be chosen such that during maxi-
mum continuous load operation the junction tempera-
ture is kept below this number. The example below
shows the steps in selecting the proper regulator heat
sink for an AMD 486DX4-120 MHz processor.
V
IN
Figure 4 - Schematic showing connection
V
IN
IRU1015
for best load regulation.
Adj
V
O U T
PARASITIC LINE
RESISTANCE
R2
R1
R
P
P(eff)
=R
08/20/02
Rev. 1.3
P
3(1+
R
L