User Manual

12-2 EP7309/11/12 User’s Manual - DS508UM4
Copyright Cirrus Logic, Inc. 2003
PWM Interface
12
PWM (Pulse Width Modulator) Register List
Programming Example
;*****************************************************************************
;ExampleturnsonPWMdriveO.SystempoweredfromACsourcefor
; 15/16 duty cycle
;*****************************************************************************
PMPCON_AC EQU 0xF0
;
ldr r0, =0x80000000
mov r1, =PMPCON_AC
str r1, [r0,#0x400]
;
Operational Overview
The device operates from the internal PLL at 96 kHz (117.6 kHz at a CPU speed of 90
MHz), and 101.6 kHz if th e external 13 MHz clock is used. These signals are intended
for use as drivers for external DC-DC converters. The P WM has a programm able
duty cycle and a built-in detection feedback pin which can be used to enable or
disable the drive.
ThePMPCONregisterisprogrammedtoactivethePWMDrivepinstogeneratea
square wave with a duty cycle that can be varied from 1 pulse in 16, to 15 pulses in 16.
Programming the value of 8 into the Drive pin registers will create a 50% duty cycle
output.
The drive pins (
Drive[1:0]) are sensed for polarity at pow er on reset. I f the pin is hig h,
the PWM signal will be active low. If low, the pin will be active high.
The
Drive[0] has the conditional capability of sensing whether the system is battery
powered or supplied by an external source by monitoring
BATOK and nEXTPWR.
Based on the activity of these pins, the EP73xx will look at the appropriate settings in
the PMPCON register.
BATOK is active high. nEXTPWR is active low.
The PWM feedback pins (
FB[1:0]) determine if the PWM is to be enabled or disabled
the PWM drive. If the value is 0, the corresponding PWM drive is turned off, and if
thevalueis1,thePWMremainsenabled.Theydonotdisabletheinternalclockthat
sources the PWM drives.
Note: To m aximize power savings, the drive fields should be used to disable the
PWMs, instead of the FB pins. The clocks that source the PWMs are disabled
when the drive ratio fields are cleared.
Table 12-1: PWM (Pulse Width Modulator) Registers
Address Name Type Size Description Page
0x8000.0400 PMPCON R/W 12 Pump (PWM) Control Register page 12-3