iru1030 International Rectifier Corp., iru1030 Datasheet - Page 6

• Manufacturer Part Number: iru1030
• Description: 3a Low Dropout Positive Adjustable Regulator
• Manufacturer: International Rectifier Corp.

IRU1030
An example of a regulator design to meet the Intel
Pentium Pro GTL+ specification 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
Pentium Pro
Processor
Type of
sistor divider tolerance is
nal), then the total step allowed for the ESR and the
ESL, is 120 mV.
Assuming that the ESL drop is 10mV, the remain-
ing ESR step will be
capacitor 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 typ.
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 [
Table 1 - GTL+ Specification for Pentium Pro
Figure 5 - Typical regulator response to
LOAD
CURRENT
V
V
110
2.7
ESL
ESR
the fast load current step.
Nominal
1.50 V
V
= 40mV
OUT
LOAD CURRENT RISE TIME
T
110mV. Therefore the output
I
2.7 A
MAX
30mV ( 2% of 1.5V nomi-
1030plt1-1.0
Output Tolerance
Max Allowed
150 mV
V
C
www.irf.com
2) With the output capacitance being 1500mF:
To set the output DC voltage, we need to select R1 and
R2:
3) Assuming R1 = 121V, 0.5%:
Finally, the input capacitor is selected as follows:
4) Assuming that the input voltage can drop 150mV be-
Selecting a single 1500mF the same type as the output
capacitors exceeds our requirements. However, the same
input capacitor can also support the second regulator
for the other end of termination.
Select R2 = 24.3V, 0.5%
Selecting both R1 and R2 resistors to be 0.5% toler-
ance, results in the least amount of error introduced
by the resistor dividers leaving
for the IRU1030 reference which is 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 2.7A load step
is given by:
The ESR should be less than:
DVc =
Where:
Dt = 2ms is the regulator response time
R2 =
C
ESR =
Where:
V
DV L Maximum regulator dropout voltage
DI L Load current step
ESR =
IN
DROP
=
(
2.7 3 50
L Input voltage drop allowed in step 4
Dt 3 DI
(V
(3.3 - 1.5 - 1.2 - 0.15)
V
V
0.15
OUT
REF
IN
C
- V
-1
)
OUT
=
3R1 =
= 900mF
DI
2.7
2 3 2.7
- DV - V
1500
(
1.25
1.5
DROP
= 3.6mV
= 0.16V
)
-1
1.3% error budget
)
3121 = 24.2V
50ms, then
08/20/02
Rev. 1.3