PIC24FJ256GA110_10 Datasheet, PDF (171/330 Pages) Microchip Technology – 64/80/100-Pin, 16-Bit, General Purpose Flash Microcontrollers with Peripheral Pin Select

PIC24FJ256GA110 FAMILY
EQUATION 14-2: CALCULATION FOR MAXIMUM PWM RESOLUTION⁽¹⁾
( ) ^log10
FCY
FPWM • (Timer Prescale Value)
Maximum PWM Resolution (bits) =
bits
log₁₀(2)
Note 1: Based on FCY = FOSC/2, Doze mode and PLL are disabled.
EXAMPLE 14-1: PWM PERIOD AND DUTY CYCLE CALCULATIONS⁽¹⁾
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) • TCY • (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 = log₁₀(FCY/FPWM)/log₁₀2) bits
= (log₁₀(16 MHz/52.08 kHz)/log₁₀2) bits
= 8.3 bits
Note 1: Based on TCY = 2 * TOSC, Doze mode and PLL are disabled.
TABLE 14-1: EXAMPLE PWM FREQUENCIES AND RESOLUTIONS AT 4 MIPS (FCY = 4 MHz)⁽¹⁾
PWM Frequency
7.6 Hz
61 Hz
122 Hz 977 Hz 3.9 kHz 31.3 kHz 125 kHz
Timer Prescaler Ratio
8
1
1
1
Period Register Value
FFFFh
FFFFh
7FFFh
0FFFh
Resolution (bits)
16
16
15
12
Note 1: Based on FCY = FOSC/2, Doze mode and PLL are disabled.
1
03FFh
10
1
007Fh
7
1
001Fh
5
TABLE 14-2: EXAMPLE PWM FREQUENCIES AND RESOLUTIONS AT 16 MIPS (FCY = 16 MHz)⁽¹⁾
PWM Frequency
30.5 Hz 244 Hz 488 Hz 3.9 kHz 15.6 kHz 125 kHz 500 kHz
Timer Prescaler Ratio
8
1
1
1
Period Register Value
FFFFh
FFFFh
7FFFh
0FFFh
Resolution (bits)
16
16
15
12
Note 1: Based on FCY = FOSC/2, Doze mode and PLL are disabled.
1
03FFh
10
1
007Fh
7
1
001Fh
5
 2010 Microchip Technology Inc.
DS39905E-page 171