AN11470

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Application note

Rev. 1 — 22 April 2014

4 of 25

NXP Semiconductors

AN11470

Leadless Schottky diodes in a DC-to-DC step-up converter

2.

Methods of DC-to-DC voltage up conversion

2.1 Voltage up conversion based on charge pumps

connected to a chopper circuit. At the secondary side the output voltage needs to be

rectified. Such a transformer approach requires two coupled coils and therefore too much

heavy material. Galvanic decoupling is a feature of this solution, but not required for a

backlight booster in mobile devices.

Another solution for voltage up conversion is a charge pump. Figure 1 depicts a circuit

that can provide an output voltage twice as high as the input voltage in case of ideal

components. With real components the forward voltage drop of the diodes leads to a

lower output voltage. Assuming the switch SW is connected to the ground GND, capacitor

connected to this higher reference point. Now charge can flow into C2 via D2 while D1 is

blocking in reverse direction. If the switch is connected to the ground again, C1 is

recharged and D2 is driven in reverse direction, because the voltage at C2 is higher than

Fig 1.

Voltage up conversion based on a charge pump

V

O

2V

I

V

F

–





=

SW

C1

GND

D1

D2

GND

GND

C2

R1