14–4
Altera Corporation
Stratix Device Handbook, Volume 2
January 2005
Voltage Regulators
Table 14–2 shows the terminology and specifications commonly
encountered with voltage regulators. Symbols are shown in parentheses.
If the symbols are different for linear and switching regulators, the linear
regulator symbol is listed first.
Table 14–2. Voltage Regulator Specifications & Terminology (Part 1 of 2)
Specification/Terminology
Description
Input voltage range (VIN,VCC)
Minimum and maximum input voltages define the input voltage range, which
is determined by the regulator process voltage capabilities.
Line regulation
(line regulation, VOUT)
Line regulation is the variation of the output voltage (VOUT) with changes in
the input voltage (VIN). Error amplifier gain, pass transistor gain, and output
impedance all influence line regulation. Higher gain results in better
regulation. Board layout and regulator pin-outs are also important because
stray resistance can introduce errors.
Load regulation
(load regulation, VOUT)
Load regulation is a variation in the output voltage caused by changes in the
input supply current. Linear Technology regulators are designed to minimize
load regulation, which is affected by error amplifier gain, pass transistor gain,
and output impedance.
Output voltage selection
Output voltage selection is adjustable by resistor voltage divider networks,
connected to the error amplifier input, that control the output voltage. There
are multiple output regulators that create 5.0-, 3.3-, 2.5-, 1.8- and 1.5-V
supplies.
Quiescent current
Quiescent current is the supply current during no-load or quiescent state.
This current is sometimes used as a general term for a supply current used
by the regulator.
Dropout voltage
Dropout voltage is the difference between the input and output voltages
when the input is low enough to cause the output to drop out of regulation.
The dropout voltage should be as low as possible for better efficiency.
Current limiting
Voltage regulators are designed to limit the amount of output current in the
event of a failing load. A short in the load causes the output current and
voltage to decrease. This event cuts power dissipation in the regulator during
a short circuit.
Thermal overload protection
This feature limits power dissipation if the regulator overheats. When a
specified temperature is reached, the regulator turns off the output drive
transistors, allowing the regulator to cool. Normal operation resumes once
the regulator reaches a normal operating temperature.
Reverse current protection
If the input power supply fails, large output capacitors can cause a substantial
reverse current to flow backward through the regulator, potentially causing
damage. To prevent damage, protection diodes in the regulator create a path
for the current to flow from VOUT to VIN.
Stability
The dominant pole placed by the output capacitor influences stability.
Voltage regulator vendors can assist you in output capacitor selection for
regulator designs that differ from what is offered.