NCP566
http://onsemi.com
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APPLICATION INFORMATION
The NCP566 low dropout linear regulator provides fixed
voltages at currents up to 1.5 A. It features ultra fast transient
response and low dropout voltage. These devices contain
output current limiting, short circuit protection and thermal
shutdown protection.
Input, Output Capacitor and Stability
Typical values of parameters in Electrical Characteristics
section and in Typical Characteristics section were
measured with input and output capacitors equal to 150 mF
unless otherwise noted.
An input bypass capacitor is recommended to improve
transient response or if the regulator is located more than a
few inches from the power source. This will reduce the
circuit’s sensitivity to the input line impedance at high
frequencies and significantly enhance the output transient
response. Different types and different sizes of input
capacitors can be chosen dependent on the quality of power
supply. The range of 4.7 mF to 150 mF should cover most of
the applications. The higher capacitance the lower change of
input voltage due to line and load transients. The bypass
capacitor should be mounted with shortest possible lead or
track length directly across the regulator’s input terminals.
The output capacitor is required for stability. The NCP566
remains stable with ceramic, tantalum, and aluminum−
electrolytic capacitors with a minimum value of 1.0 mF with
ESR between 50 mW and 2.5 W. The range of 2.2 mF to
150 mF should cover most of the applications. The higher
capacitance the better load transient response. When a high
value capacitor is used, a low value capacitor is also
recommended to be put in parallel. The NCP566 is
optimized for use with a 150 mF OSCON 16SA150M type
in parallel with a 10 mF OSCON 10SL10M type from Sanyo.
The 10 mF capacitor is used for best AC stability while
150 mF capacitor is used for achieving excellent load
transient response. The output capacitors should be placed
as close as possible to the output pin of the device. If not, the
excellent load transient response of NCP566 will be
degraded.
Load Transient Measurement
Large load current changes are always presented in
microprocessor applications. Therefore good load transient
performance is required for the power stage. NCP566 has
the feature of ultra fast transient response. Its load transient
responses in Figures 11 through 14 are tested on evaluation
board shown in Figure 17. The evaluation board consists of
NCP566 regulator circuit with decoupling and filter
capacitors and the pulse controlled current sink to obtain
load current transitions. The load current transitions are
measured by current probe. Because the signal from current
probe has some time delay, it causes un−synchronization
between the load current transition and output voltage
response, which is shown in Figures 11 through 14.
NCP566
Evaluation Board
GEN
GND
V
RL
GND
Scope Voltage Probe
+
+
Pulse
Figure 17. Schematic for Transient Response Measurement
V
out
−V
CC
V
in
