SLOSE98A December 2022 – September 2023 DRV8461
PRODUCTION DATA
Spread spectrum or frequency dithering is used to reduce the effect of EMI by converting a narrowband signal into a wideband signal, which will spread the energy across multiple frequencies. Figure 7-36 illustrates how manipulating the clock frequency over time has the effect of spreading the energy.
In the context of the DRV8461, the frequencies of the internal clock for digital circuits (10 MHz typical) and the clock for charge pump (357 kHz typical) are manipulated to reduce the peak energy and is distributed to other frequencies and their harmonics. This feature combined with output slew rate control minimizes the radiated emissions from the device and helps pass strict EMI standards.
When the DRV8461 is configured with the SPI interface, spread spectrum can be enabled or disabled by the DIS_SSC bit. By default, spread spectrum is disabled after power-up. Writing 0b to the DIS_SSC bit enables spread spectrum. If the device is operating with silent step decay mode, spread spectrum is disabled. Additionally, when the DRV8461 is configured with the GPIO interface, spread spectrum is disabled.
There are many ways to implement spread spectrum. The DRV8461 uses the triangular analog modulation profile. Figure 7-37 and Figure 7-38 show the spread spectrum profiles of the internal digital clock and the charge pump clock around their respective centre frequencies. The digital clock varies by equal amounts over 14 steps between 9 MHz and 11 MHz.
Note that the centre frequencies themselves will vary with process and temperature changes, and the variations due to spread spectrum will be in addition to those.