PIC24HJ12GP201 Datasheet, PDF (123/234 Pages) Microchip Technology – High-Performance, 16-Bit Microcontrollers

PIC24HJ12GP201/202
EXAMPLE 13-1: PWM PERIOD AND DUTY CYCLE CALCULATIONS
1. Find the Timer Period register value for a desired PWM frequency that is 52.08 kHz, where FCY = 16 MHz and a Timer2
prescaler setting of 1:1.
TCY
= 62.5 ns
PWM Period = 1/PWM Frequency = 1/52.08 kHz = 19.2 ms
PWM Period = (PR2 + 1) • TCY • (Timer2 Prescale Value)
19.2 ms
= (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
TABLE 13-1: EXAMPLE PWM FREQUENCIES AND RESOLUTIONS AT 4 MIPS (FCY = 4 MHz)
PWM Frequency
7.6 Hz
61 Hz
122 Hz 977 Hz 3.9 kHz 31.3 kHz 125 kHz
Timer Prescaler Ratio
Period Register Value
Resolution (bits)
8
FFFFh
16
1
FFFFh
16
1
7FFFh
15
1
0FFFh
12
1
03FFh
10
1
007Fh
7
1
001Fh
5
TABLE 13-2: EXAMPLE PWM FREQUENCIES AND RESOLUTIONS AT 16 MIPS (FCY = 16 MHz)
PWM Frequency
30.5 Hz 244 Hz 488 Hz 3.9 kHz 15.6 kHz 125 kHz 500 kHz
Timer Prescaler Ratio
Period Register Value
Resolution (bits)
8
FFFFh
16
1
FFFFh
16
1
7FFFh
15
1
0FFFh
12
1
03FFh
10
1
007Fh
7
1
001Fh
5
TABLE 13-3: EXAMPLE PWM FREQUENCIES AND RESOLUTIONS AT 40 MIPS (FCY = 40 MHz)
PWM Frequency
76 Hz
610 Hz 1.22 Hz 9.77 kHz 39 kHz 313 kHz 1.25 MHz
Timer Prescaler Ratio
Period Register Value
Resolution (bits)
8
FFFFh
16
1
FFFFh
16
1
7FFFh
15
1
0FFFh
12
1
03FFh
10
1
007Fh
7
1
001Fh
5
© 2007 Microchip Technology Inc.
Preliminary
DS70282B-page 121