7.3.4 Ramp Signal

The TPS53219A adds a ramp signal to the 0.6-V reference in order to improve jitter performance. As described in Small Signal Model, the feedback voltage is compared with the reference information to keep the output voltage in regulation. By adding a small ramp signal to the reference, the S/N ratio at the onset of a new switching cycle is improved. Therefore the operation becomes less jittery and more stable. The ramp signal is controlled to start with –7 mV at the beginning of an on-cycle and becomes 0 mV at the end of an off-cycle in steady-state.

During skip mode operation, when the switching frequency is lower than 70% of the nominal frequency (because of longer OFF-time), the ramp signal exceeds 0 mV at the end of the OFF-time but is clamped at 3 mV to minimize DC offset.