NCP3064 Datasheet, PDF (7/20 Pages) ON Semiconductor – 1.5 A, Step-Up/Down/ Inverting Switching Regulator with ON/OFF Function

NCP3064, NCP3064B, NCV3064
INTRODUCTION
The NCP3064 is a monolithic power switching regulator
optimized for dc to dc converter applications. The
combination of its features enables the system designer to
directly implement step−up, step−down, and
voltage−inverting converters with a minimum number of
external components. Potential applications include cost
sensitive consumer products as well as equipment for
industrial markets. A representative block diagram is shown
in Figure 4.
Operating Description
The NCP3064 is a hysteric, dc−dc converter that uses a
gated oscillator to regulate output voltage. In general, this
mode of operation is some what analogous to a capacitor
charge pump and does not require dominant pole loop
compensation for converter stability. The Typical Operating
Waveforms are shown in Figure 13. The output voltage
waveform shown is for a step−down converter with the
ripple and phasing exaggerated for clarity. During initial
converter startup, the feedback comparator senses that the
output voltage level is below nominal. This causes the
output switch to turn on and off at a frequency and duty cycle
controlled by the oscillator, thus pumping up the output filter
capacitor. When the output voltage level reaches nominal,
the output switch next cycle turning on is inhibited. The
feedback comparator will enable the switching immediately
when the load current causes the output voltage to fall below
nominal. Under these conditions, output switch conduction
can be enabled for a partial oscillator cycle, a partial cycle
plus a complete cycle, multiple cycles, or a partial cycle plus
multiple cycles.
Oscillator
The oscillator frequency and off−time of the output switch
are programmed by the value selected for the timing
capacitor C_T. Capacitor C_T is charged and discharged by a
1 to 6 ratio internal current source and sink, generating a
positive going sawtooth waveform at Pin 3. This ratio sets
the maximum t_ON/(t_ON + t_OFF) of the switching converter as
6/(6 + 1) or 0.857 (typical).
The oscillator peak and valley voltage difference is
500 mV typically. To calculate the C_T capacitor value for the
required oscillator frequency, use the equation found in
Figure 15. An Excel® based design tool can be found at
www.onsemi.com on the NCP3064 product page.
Figure 13. Typical Operating Waveform
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