IRU1015CM International Rectifier, IRU1015CM Datasheet - Page 6

• Manufacturer Part Number: IRU1015CM
• Description: IC REG ADJ LDO 1.5A TO-263-3
• Manufacturer: International Rectifier

Specifications of IRU1015CM

• 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-263-3, D²Pak (3 leads + Tab), TO-263AA
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Other names: *IRU1015CM; IRU1015-CM; IRU1015-CM

IRU1015
An example of a regulator design to meet the AMD speci-
fication for 486DX4-120MHz is given below.
Assume the specification for the processor as shown in
Table 1:
The first step is to select the voltage step allowed in the
output due to the output capacitor’s ESR:
1) Assuming the regulator’s initial accuracy plus the re-
6
AMD 486DX4
Processor
sistor divider tolerance is
nominal), then the total step allowed for the ESR and
the ESL, is -64mV.
Assuming that the ESL drop is -10mV, the remaining
ESR step will be -54mV. Therefore the output ca-
pacitor ESR must be:
The Sanyo MVGX series is a good choice to achieve
both price and performance goals. The 6MV1500GX,
1500mF, 6.3V has an ESR of less than 36mV typi-
cal. Selecting a single capacitor achieves our design
goal.
The next step is to calculate the drop due to the ca-
pacitance discharge and make sure that this drop in
voltage is less than the selected ESL drop in the
previous step.
ESR [
Type of
Table 1 - GTL+ specification for Pentium Pro
Figure 5 - Typical regulator response
LOAD
CURRENT
1.2
V
V
54
to the fast load current step.
ESL
ESR
= 45mV
Nominal
V
3.45 V
LOAD CURRENT RISE TIME
T
OUT
1.2 A
I
±86mV (±2.5% of 3.45V
MAX
1015plt1-1.0
Output Tolerance
Max Allowed
150 mV
V
C
www.irf.com
2) With the output capacitance being 1500mF:
To set the output voltage, we need to select R1 and R2:
3) Assuming R1=121V, 1%
Finally, the input capacitor is selected as follows:
4) Assuming that the input voltage can drop 150mV be-
Selecting both R1 and R2 resistors to be 1% toler-
ance results in the least amount of error introduced
by the resistor dividers leaving a
get for the IRU1015 reference which is well within the
initial accuracy of the device.
fore the main power supply responds, and that the
main power supply response time is
the minimum input capacitance for a 1.2A load step
is given by:
The ESR should be less than:
Select a single 1500mF the same type as the output
capacitors exceeds our requirements. Figure 6 shows
the completed schematic for our example.
DVc =
Where:
Dt = 2ms is the regulator response time
R2 =
Select R2 = 215V, 1%
C
ESR =
Where:
DV L Maximum regulator dropout voltage
V
DI L Load current step
ESR =
IN
DROP
=
(
1.2 3 50
L Input voltage drop allowed in step 4
Dt 3 DI
0.15
(V
(5 - 3.45 - 1.2 - 0.15)
V
V
OUT
REF
IN
C
- V
-1
)
OUT
3R1 =
= 400mF
DI
1.2
=
- DV - V
2 3 1.2
1500
(
3.45
1.25
DROP
= 0.167V
= 1.6mV
)
-1
)
±2.5% error bud-
3121 = 213V
50ms, then
08/20/02
Rev. 1.3