NCP5608

http://onsemi.com

7

APPLICATIONS INFORMATION

DC−DC OPERATION

The converter is based on a charge pump technique to

generate a DC voltage capable to supply the white LED

load. The system regulates the current flowing into each

LED by means of internal current mirrors associated with

the white diodes. Consequently, the output voltage will be

equal to the Vf of the LED, plus the 300 mV (typical)

developed across the internal NMOS mirror. Typically,

assuming a standard white LED forward biased at 10 mA,

the output voltage will be 3.2 V.

The third external capacitor makes possible the 1.33X

extra mode of operation, with a significant efficiency

improvement of the converter over the normal battery

voltage span. The threshold levels have been defined to

optimize this range of operating voltages, assuming a high

efficiency is not relevant when the system is connected to

a battery charger (i.e. Vbat > 4.5 V).

The built−in OVP circuit continuously monitors each

output and stops the converter when the voltage is above

5.0 V. The converter resumes normal operation when the

voltage drops below 5.0 V (no latch−up mechanism).

Consequently, the chip can operate with no load during any

test procedures, but in the case of special applications, it is

recommended to connect the unused LED driver either to

The structure is built with power MOS devices to

accommodate the modes selected by the analog functions.

The current flowing into each LED is continuously

regulated

according

to

the

value

defined

by

the

programming message. The total current is limited

to

500 mA DC.

The system runs with two cycles:

− Cycle#1

Fly capacitors are charged from the battery.

− Cycle#2

Energy accumulated into the fly capacitors is

transferred to the load.

PIN 16

GND

PWRGND

Q2

PIN 19

C1

C1N

C1P

PIN 17

Q8

C2

C2P

PIN 21

Q12

C3

C3P

PIN 22

Q1

Q6

Q10

Q11

Q3

Q7

Q4

Q5

Q9

PIN 23

PIN 20

CURRENT CONTROL

PIN 18

PIN 13

LEDx

GND

C2N

C3N

Li−Ion

2.90 V − 4.10 V

Figure 3. Basic DC−DC NCP5608 Converter Structure

GND