Smart Control of Internal Supply Voltage Spikes in a Low Voltage DC-DC Buck Converter

摘要

A smart dual slope gate driver for CMOS integrated low voltage DC-DC buck converters is proposed. The proposed driver reduces the switching losses and limits the magnitude of the internal voltage spikes caused by current variations on the parasitic inductances inbuilt in the converter power supply path. The dual slope gate driver has two strengths: a weak (slow) and a strong one (fast) which time duration is dynamically adjusted in order to control the time of the opening phase of the buck convertor active switch when the fastest variation of the current occurs. The magnitude of the voltage spikes in the internal power supply nodes depends on the time derivative of the current in the parasitic inductances, and can be hazardous to the chip, especially when a high current is switched at a high frequency. To overcome this problem, a common solution is to increase the turn-off time of the active switch at a cost of a reduced switching frequency and efficiency. To increase the power density of integrated low voltage DC-DC converters, the switching frequency must be increased and soft switching techniques were proposed to reduce the switching losses and to absorb the parasitic inductances and capacitances. However, these solutions increase the control complexity and cause higher voltage or current stress on the switches. Hard switching converters integrated with low voltage standard CMOS technologies can be used with high switching frequencies if new gate drivers are designed. The proposed smart dual slope gate drive reduces the internal supply voltage spikes of a DC-DC buck converter by dynamically adjusting the driver strength in order to increase the efficiency even with high switching frequencies. The dual slope drive is explained and results from a buck converter designed in a 0.13 μm standard CMOS technology are discussed in terms of the impact on high level design parameters, mainly on the switching losses and on the voltage spike magnitude reduction.