AMC7580 Datasheet, PDF (6/12 Pages) List of Unclassifed Manufacturers – 7A LOW DROPOUT REGULATOR

AMC DOC. #: AMC7580_E (LF)
Feb 2005
AMC7580
7A LOW DROPOUT REGULATOR
APPLICATION INFORMATION
General
The AMC7580 series is designed to power the new generation of microprocessors. It is designed to make use of
multiple power supplies, present in most systems, to reduce the dropout voltage. One of the advantages of the two-
supply approach is maximizing the efficiency.
The second supply is at least 1V greater than output voltage and is providing the power for the control circuitry and
supplies the drive current to the NPN output transistor. This allows the NPN output transistor to be driven into
saturation. For the control voltage the current requirement is small, about 1% of the output current or approximately
50 mA for a 7A load. This drive current becomes part of the output current. The maximum voltage on the Control
pin is 13 V. The maximum voltage at the Power pin is 7 V. By trying the control and power inputs together the
AMC7580 can also be operated as a single supply device. In single supply operation, the dropout voltage will be
determined by the minimum the Control voltage.
The new generation of microprocessors cycle load current from several hundred milliamperes to several amperes in
tens of nanoseconds. Output voltage tolerances are tighter and include transient response as part of the specification.
Designed to meet the fast current load step requirements of these microprocessors, the AMC7580-X.X also saves
total cost by needing less output capacitance to maintain regulation.
The sense pin permits very accurate regulation of output voltage. As a result, over an output current range of 100mA
to 7A, the typical load regulation is less than 1mV.
In addition to the enhancements mentioned, the reference accuracy has been improved a factor of two with a
guaranteed initial tolerance of ±1% at 25°C and 1.6% accuracy over the full temperature and load current range.
Typical applications for the AMC7580 include 3.3V to 2.5 V conversion with a 5V control supply, 5V to 4.2V
conversion with a 12V control supply or 5V to 3.6V conversion with a 12V control supply. It is easy to obtain
dropout voltages of less than 0.5V at 2.5A along with excellent static and dynamic specifications. The device is fully
protected against over current and over temperature conditions.
Grounding and Output Sensing
The AMC7580-ADJ allows true Kelvin sensing for both the high and low side of the load. As a result the voltage
regulation at the load can be easily optimized. Voltage drops due to parasitic resistances between the regulator and
the load can be placed inside the regulation loop. The advantages of remote sensing are illustrated in figures 1
through 3.
Figure 1 shows the device connected as a conventional 3 terminal regulator with the Sense lead connected directly to
the output of the device. Rp is the parasitic resistance of the connections between the device and the load. Trace A of
figure 3 illustrates the effect of Rp.
Figure 2 shows the device connected to take advantage of the remote sense feature. The Sense pin and the top of the
resistor divider are connected to the top of the load; the bottom of the resistor divider is connected to the bottom of
the load. The effect on output regulation can be seen in trace B of figure 3.
It is important to note that the voltage drops due to Rp are not eliminated; they will add to the dropout voltage of the
regulator regardless. TheAMC7580-ADJ can control the voltage at the load as long as the input-output voltage is
greater than the total of the dropout voltage of the device plus the voltage drop across Rp.
Copyright © 2002, ADD Microtech Corp.
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