NCP5608 查看數據表（PDF） - ON Semiconductor

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NCP5608

Multiple LED Charge Pump Driver

ON Semiconductor 

NCP5608

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 VOUT supply to avoid any uncontrolled operation.

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.

Li−Ion

2.90 V − 4.10 V

GND

PIN 19

Q1

Q3

C1N

PIN 16

C1 C1P

PIN 17

Q2

Q4

Q6

Q7

Q5 C2N

C2 C2P

PIN 20

PIN 21

Q8

Q10

Q11

Q9

C3N

C3 C3P

PIN 23

PIN 22

Q12

GND

CURRENT CONTROL

LEDx

VOUT

PIN 18

PWRGND

PIN 13

GND

Figure 3. Basic DC−DC NCP5608 Converter Structure

http://onsemi.com

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