In the LMR436x0-Q1 family of devices, spread spectrum is a factory option. To find which parts have spread spectrum enabled, see the Device Comparison Table.
Spread spectrum eliminates peak emissions at specific frequencies by spreading these peaks across a wider range of frequencies than a part with fixed-frequency operation. The LMR436x0-Q1 implements a modulation pattern designed to reduce low frequency-conducted emissions from the first few harmonics of the switching frequency. The pattern can also help reduce the higher harmonics that are more difficult to filter, which can fall in the FM band. These harmonics often couple to the environment through electric fields around the switch node and inductor. The LMR436x0-Q1 uses a spread of frequencies which can spread energy smoothly across the FM and TV bands. The device implements dual random spread spectrum (DRSS). DRSS is a combination of a triangular frequency spreading pattern and pseudorandom frequency hopping. The combination allows the spread spectrum to be very effective at spreading the energy at the following:
The advantage of DRSS is its equivalent harmonic attenuation in the upper frequencies with a smaller fundamental frequency deviation. This reduces the amount of input current and output voltage ripple that is introduced at the modulating frequency. Additionally, the LMR436x0-Q1 also allows the user to further reduce the output voltage ripple caused by the spread spectrum modulating pattern.
The spread spectrum is only available while the clock of the device is free running at its natural frequency. Any of the following conditions overrides spread spectrum, turning it off: