Datasheet

 2010 Microchip Technology Inc. DS39905E-page 171
PIC24FJ256GA110 FAMILY
EQUATION 14-2: CALCULATION FOR MAXIMUM PWM RESOLUTION
(1)
EXAMPLE 14-1: PWM PERIOD AND DUTY CYCLE CALCULATIONS
(1)
TABLE 14-1: EXAMPLE PWM FREQUENCIES AND RESOLUTIONS AT 4 MIPS (FCY = 4 MHz)
(1)
TABLE 14-2: EXAMPLE PWM FREQUENCIES AND RESOLUTIONS AT 16 MIPS (F
CY = 16 MHz)
(1)
PWM Frequency 7.6 Hz 61 Hz 122 Hz 977 Hz 3.9 kHz 31.3 kHz 125 kHz
Timer Prescaler Ratio 8111111
Period Register Value FFFFh FFFFh 7FFFh 0FFFh 03FFh 007Fh 001Fh
Resolution (bits) 16 16 15 12 10 7 5
Note 1: Based on F
CY = FOSC/2, Doze mode and PLL are disabled.
PWM Frequency 30.5 Hz 244 Hz 488 Hz 3.9 kHz 15.6 kHz 125 kHz 500 kHz
Timer Prescaler Ratio 8111111
Period Register Value FFFFh FFFFh 7FFFh 0FFFh 03FFh 007Fh 001Fh
Resolution (bits) 16 16 15 12 10 7 5
Note 1: Based on F
CY = FOSC/2, Doze mode and PLL are disabled.
(
)
Maximum PWM Resolution (bits) =
F
CY
FPWM • (Timer Prescale Value)
log
10
log
10
(2)
bits
Note 1: Based on FCY = FOSC/2, Doze mode and PLL are disabled.
1. Find the Timer Period register value for a desired PWM frequency of 52.08 kHz, where FOSC = 8 MHz with PLL
(32 MHz device clock rate) and a Timer2 prescaler setting of 1:1.
TCY = 2 * TOSC = 62.5 ns
PWM Period = 1/PWM Frequency = 1/52.08 kHz = 19.2 s
PWM Period = (PR2 + 1) • T
CY • (Timer2 Prescale Value)
19.2 s = (PR2 + 1) • 62.5 ns • 1
PR2 = 306
2. Find the maximum resolution of the duty cycle that can be used with a 52.08 kHz frequency and a 32 MHz device clock rate:
PWM Resolution = log
10
(FCY/FPWM)/log
10
2) bits
=(log
10
(16 MHz/52.08 kHz)/log
10
2) bits
= 8.3 bits
Note 1: Based on TCY = 2 * TOSC, Doze mode and PLL are disabled.