Altera Stratix - Selecting Voltage Regulators

Altera Corporation 14–9
January 2005 Stratix Device Handbook, Volume 2
Designing with 1.5-V Devices
Selecting Voltage Regulators
Your design requirements determine which voltage regulator you need.
The key to selecting a voltage regulator is understanding the regulator
parameters and how they relate to the design.
The following checklist can help you select the proper regulator for your
design:
■ Do you require a 3.3-V, 2.5-V, and 1.5-V output (V
OUT
)?
■ What precision is required on the regulated 1.5-V supplies (line and
load regulation)?
■ What supply voltages (V
IN
or V
CC
) are available on the board?
■ What voltage variance (input voltage range) is expected on V
IN
or
V
CC
?
■ What is the maximum I
CC
(I
OUT
) required by your Altera
®
device?
■ What is the maximum current surge (I
OUT(MAX)
) that the regulator
will need to supply instantaneously?
Choose a Regulator Type
If required, select either a linear, asynchronous switching, or
synchronous switching regulator based on your output current, regulator
efficiency, cost, and board-space requirements. DC-to-DC converters
have output current capabilities from 1 to 8 A. You can use a controller
with an external MOSFET rated for higher current for higher-output-
current applications.
Calculate the Maximum Input Current
Use the following equation to estimate the maximum input current based
on the output power requirements at the maximum input voltage:
Where η is nominal efficiency: typically 90% for switching regulators,
60% for linear 2.5-V-to-1.5-V conversion, 45% for linear 3.3-V-to-1.5-V
conversion, and 30% for linear 5.0-V-to-1.5-V conversion.
Once you identify the design requirements, select the voltage regulator
that is best for your design. Tables 14–5 and 14–6 list a few Linear
Technology and Elantec regulators available at the time this document
I
IN,DC(MAX)
=
V
OUT
× I
OUT(MAX)
η × V
IN(MAX)