Cirrus Logic EP73xx - Manual (Page 107)

EP7309/11/12 User’s Manual - DS508UM4 12-1
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Copyright Cirrus Logic, Inc. 2003
1212
12
Chapter 12
12 PWM 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
FB 1
V-
V+
+
-
V DD
F B0
V+
V ref
Vref
Com parator
Com parator
DC-DC Circuit
PW M Drive0
PW M Drive1
0V
0V
V-
10K
10K
VDD
GND
10K
10K
Figure 12-1. Block Diagram of a Power Supply Using Two PWM Drives