SLLSFX9 December 2024 MCF8316D
PRODUCTION DATA
MCF8316D provides the option of PWM dithering to reduce the EMI generated by MOSFET switching - when enabled, the PWM switching frequency is varied continuously (within a user configured frequency range) around the PWM_FREQ_OUT setting to spread the EMI energy across the frequency spectrum and reduce the EMI peak values. The user configured frequency range for PWM dithering is set by PWM_DITHER_DEPTH; setting PWM_DITHER_DEPTH to 0x0 disables PWM dithering. PWM_DITHER_DEPTH provides ±5%, ±7.5% and ±10% frequency spread options. When PWM_FREQ_OUT is set to 25kHz and PWM_DITHER_DEPTH is set to ±10%, the PWM switching frequency applied to the MOSFETs continuously varies between 22.5kHz (25kHz-10%) and 27.5kHz (25kHz+10%), thereby reducing the EMI peaks at multiples of 25kHz. PWM dithering is available in two modes - random or triangular (configured by PWM_DITHER_MODE). In random dithering, the PWM switching frequency is continuously varied randomly within the range set by PWM_FREQ_OUT and PWM_DITHER_DEPTH. In triangular dithering, the PWM switching frequency is varied at user configured slew rate (configured by PWM_DITHER_STEP) as shown in Figure 6-51.
The PWM switching frequency slew rate (PWM_DITHER_SLEW in Figure 6-51) is set as shown in Equation 10.
SLEW_SCALING FACTOR varies with PWM switching frequency as listed in Table 6-5.
PWM switching frequency (kHz) | SLEW_SCALING FACTOR |
---|---|
10 | 1 |
15 | 2.25 |
20 | 2 |
25 | 3.125 |
30 | 4.5 |
35 | 3.0625 |
40 | 4 |
45 | 5.0625 |
50 | 6.25 |
55 | 7.5625 |
60 | 9 |