AN-8023 Datasheet, PDF (1/6 Pages) Fairchild Semiconductor – Negative Voltage Management

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AN-8023
Negative Voltage Management Using a
FAN8303 Buck Regulator
Abstract
FAN8303 is a 2A, 370kHz monolithic integrated buck
regulator with internal power MOSFETs. It is simple to use
and needs minimal external components. This application
note describes how to generate negative voltage using
FAN8303. It introduces application examples and discusses
optimized designs for a buck-boost circuit.
Introduction
Buck regulators are widely used for higher voltage to lower
voltage DC conversion. Likewise, FAN8303 was originally
designed for application needing regulated DC voltage, such
as set-top box microcontrollers and efficient pre-regulators
for linear regulators in PC monitor and TV applications. In
some cases, a non-synchronous buck regulator also can be
utilized for buck-boost circuit to generate negative voltage
with respect to ground. These applications include audio
amplifier, timing control circuit for LCD panel, and so on.
Figure 1 shows a practical application of an LCD panel; it
needs negative voltage for contrast control. In this block
diagram, a charge pump is usually adopted due to the simple
design and low cost. However, it has an amount of power
dissipation and poor output voltage regulation relative to
input voltage variation. FAN8303 with negative output
would be a solution to overcome these problems.
12V
AV Board
Charge pump
LDO
2.5V, 3.3V
-5V , 15V
SoC
DC/DC (buck) ^2.5V
DC/DC (boost)
DDR2 EEPROM
16V
Figure 1. Example of Timing Control Block
© 2009 Fairchild Semiconductor Corporation
Rev. 1.0.0 • 7/30/09
TFT LCD Panel
Column Drivers
P-gamma IC
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