NCP565(2004) Просмотр технического описания (PDF) - ON Semiconductor
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NCP565 Datasheet PDF : 12 Pages
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NCP565
APPLICATION INFORMATION
The NCP565 low dropout linear regulator provides
adjustable 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
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. A 150 mF OSCON 16SA150M type from Sanyo
should be adequate for most applications. 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 NCP565
remains stable with ceramic, tantalum, and aluminum−
electrolytic capacitors with a minimum value of 1.0 mF as
long as the ESR remains between 50 mW and 2.5 W. The
NCP565 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 output 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
NCP565 will be degraded.
Adjustable Operation
The typical application circuit for the adjustable output
regulators is shown in Figure 1. The adjustable device
develops and maintains the nominal 0.9 V reference voltage
between Adj and ground pins. A resistor divider network R1
and R2 causes a fixed current to flow to ground. This current
creates a voltage across R1 that adds to the 0.9 V across R2
and sets the overall output voltage.
The output voltage is set according to the formula:
ǒ Ǔ Vout + Vref
R1 ) R2
R2
* IAdj
R2
The adjust pin current, Iadj, is typically 30 nA and
normally much lower than the current flowing through R1
and R2, thus it generates a small output voltage error that can
usually be ignored.
Load Transient Measurement
Large load current changes are always presented in
microprocessor applications. Therefore good load transient
performance is required for the power stage. NCP565 has
the feature of ultra fast transient response. Its load transient
responses in Figures 9 through 12 are tested on evaluation
board shown in Figure 15. On the evaluation board, it
consists of NCP565 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 9
through 12.
GEN
Vout
Pulse
−VCC
Vin
+
NCP565
Evaluation Board
V
RL
GND
+
GND
Scope Voltage Probe
Figure 15. Schematic for Transient Response Measurement
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