Cirrus-logic EP73xx Manual de usuario Pagina 107

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EP7309/11/12 Users Manual - DS508UM4 12-1
Copyright Cirrus Logic, Inc. 2003
1212
12
Chapter 12
12PWM Interface
Introduction
There are two PWM (Pulse Width Modulator) outputs. This was designed for DC to
DC conversion circuits but can be used for other types of controls. Typical use
includes backlight voltage for LCDs and programmable LCD contrast voltages.
Features
Operates from Internal PLL or external 13 MHz clock
Programmable duty cycle
Feedback circuit control
Power monitor for external AC or battery use
Block Diagram
The block diagram below illustrates a typical design using both PWM drives in a
power supply.
V-
V+
+
-
VDD
FB1
V-
V+
+
-
VDD
FB0
V+
Vref
Vref
Comparator
Comparator
DC-DC Circuit
PWM Drive0
PWM Drive1
0V
0V
V-
10K
10K
VDD
GND
10K
10K
Figure 12-1. Block Diagram of a Power Supply Using Two PWM Drives
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