NCP3065 查看數據表（PDF） - ON Semiconductor

零件编号

产品描述 (功能)

生产厂家

NCP3065

Up to 1.5 A Constant Current Switching Regulator for LEDs

ON Semiconductor 

NCP3065, NCV3065

INTRODUCTION

The NCP3065 is a monolithic power switching regulator

optimized for LED Driver applications. Its flexible

architecture enables the system designer to directly

implement a step-up or step-down topology with a

minimum number of external components for driving LEDs.

A representative block diagram is shown in Figure 4.

OPERATING DESCRIPTION

The NCP3065 operates as a fixed oscillator frequency

output voltage ripple gated regulator. In general, this mode

of operation is somewhat 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 14. 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 feedback voltage level reaches nominal

comparator value, the output switch cycle is inhibited. When

the load current causes the output voltage to fall below the

nominal value feedback comparator enables switching

immediately. Under these conditions, the 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 of the timing capacitor CT.

Capacitor CT 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

tON/(tON+tOFF) of the switching converter as 6/(6+1) or

85.7% (typical). The oscillator peak and valley voltage

difference is 500 mV typically. To calculate the CT capacitor

value for required oscillator frequency, use the equations

found in Figure 22. An online NCP3065 design tool can be

found at www.onsemi.com, which adds in selecting

component values.

1

Feedback Comparator Output

0

1

IPK Comparator Output

0

Timing Capacitor, CT

On

Output Switch

Off

Nominal Output Voltage Level

Output Voltage

Startup

Operation

Figure 14. Typical Operating Waveforms

http://onsemi.com

7

Share Link: