NCP5030

http://onsemi.com

9

Operation

The NCP5030 DC−DC converter is based on a Current

Mode PWM architecture specifically designed to

efficiently provide a regulated current to a high current

white LED. This device utilizes fixed frequency

synchronous buck−boost switching regulator architecture.

This topology is critical in single cell Lithium−Ion/

Polymer battery or 3 Alkaline powered applications as the

forward voltage of the LED may be greater than or less than

the battery voltage. A low feedback voltage of 200 mV

(nom) minimizes power losses in the current setting

resistor connected between the cathode of the LED and

ground.

The core switching regulator is configured as a full

maximize efficient power delivery. Another advantage of

this topology is that it supports a true−shut down mode

where the LED will be disconnected from the power supply

when the device is placed in disable mode.

Figure 16 shows how the four switches are connected to

through the inductor.

L

LX1

N1

LX2

N2

P1

P2

Figure 16. Basic Power Switches Topology

The converter operates in three different modes as a

this tow thresholds.

Buck

2− Phase

Buck−Boost

Boost

2− Phase

3− Phase

Figure 17. Conversion Mode

The internal oscillator provides a 700 kHz clock signal

to trigger the PWM controller on each rising edge (SET

signal) which starts a cycle. In pure buck or boost mode, the

converter operates in two−phase mode, the first one to

charge the inductor, followed by a synchronous rectifier

discharge phase. However, in buck−boost mode, to get high

efficiency the converter controls the switches in three

separate phases (see Buck−Boost Mode Section). The

smooth output voltage thus constantly powering the load.

In Buck mode, switches P1 and N1 are toggling and the

two others are fixed, the switch N2 is all time OFF and the

switch P2 is all time ON. The buck converter operates in

is OFF and the current increases through the inductor. The

switch current is measured by the SENSE CURRENT and

added to the RAMP COMP signal. Then PWM COMP

compares the output of the adder and the signal from

ERROR AMP. When the comparator threshold is

turned OFF and N1 is ON until next clock rising edge. The

current is only delivered by the inductor, which means that

LX1

LX2

Start

Cycle

1.43 mS

Figure 18. Basic DC−DC Buck Operation

The switches in boost mode are inversely controlled than

in buck mode. Switches P2 and N2 are toggling and the two

others are fixed. Switch P1 is all time ON and the switch N1

is all time OFF. The boost converter operates in two