The device supports spread-spectrum modulation of the regulator's switching clocks. Two factory-selectable modulation modes are available The first mode is external modulation which modulates the input clock at the SYNC_IN pin. The second mode is internal Adaptively Randomized Spread-Spectrum (ARSS) modulation which is based on the internal oscillator (MODCLK).

An external modulation is limited by the PLL bandwidth. The minimum time step between any two frequency changes is 50 µs. The maximum frequency change with each frequency step is 100 kHz. When the switching clocks are configured for external modulation, the device starts up with the regulator switching clocks generated from the free-running VCO clock. After the regulators ramp up and the NRES pin is driven high, an MCU can provide the input clock for the SYNC_IN pin.

The internal modulation from the MODCLK oscillator allows for maximum frequency spread from 1.79 MHz to 2.398 MHz and with a center frequency of 2.1 MHz. More details about internal Adaptively Randomized Spread-Spectrum (ARSS) modulation are covered in application note TPS65313-Q1 EMC Validation Report.

For both modulation modes, the maximum ±17% modulation spread is required to prevent false clock monitoring errors because of ±20% clock monitoring accuracy. If this maximum modulation spread exceeds ±17%, then it could result in false clock-monitoring warnings, which have a threshold set at ±17% from the nominal monitoring clock frequency.

The internal ARSS modulation is disabled by default and can be enabled and configured after power up when the device is in the DIAGNOSTIC state. Internal ARSS modulation is activated by setting the SSM_EN control bit in the SAFETY_CFG3 register.

When an internal ARSS modulation is enabled and configured, it can be disabled by the system MCU when the device is in the DIAGNOSTIC state or when the device goes into the OFF state. The device transition to the RESET state does not impact the internal ARSS modulation when it is enabled and configured.