A Bootstrap Structure Directly Charged by BUS Voltage with Threshold-Based Digital Control for High-Speed Buck Converter

Abstract

This article proposes a high-frequency, area-efficient high-side bootstrap circuit with threshold-based digital control (TBDC) that is directly charged by BUS voltage (DCBV). In the circuit, the voltage of the bootstrap is directly obtained from the BUS voltage instead of the on-chip low dropout regulator (LDO), which is more suitable for a high operating frequency. An area-efficient threshold-based digital control structure is used to detect the bootstrap voltage, thereby effectively preventing bootstrap under-voltage or over-voltage that may result in insufficient driving capability, increased loss, or breakdown of the power device. The design and implementation of the circuit are based on CSMC 0.25 µm 60 V BCD technology, with an overall chip area of 1.4 × 1.3 mm2, of which the bootstrap area is 0.149 mm2 and the figure-of-merit (FOM) is 0.074. The experimental results suggest that the bootstrap circuit can normally operate at 5 MHz with a maximum buck converter efficiency of 83.6%. This work plays a vital role in promoting the development of a wide range of new products and new technologies, such as integrated power supplies, new energy vehicles, and data storage centers.

Performance of MOSFET Driven via a Bootstrap Capacitor for Dynamic Load Continuity Enhancement

“…e design of the BSC includes three main parts; the drive circuit, the MOSFET switch parameters, the BSD ratings, and the BSC specifications. e bootstrap capacitor is charged only when the low-side power switch is turned on and discharged when a high-side switch is turned on [17][18][19]. To maintain gate-source voltage within an acceptable minimum value, the capacitor voltage drop must be…”

“…e charge required by the internal level shifter according to the rated applied voltage is in the range (3-20 nC) for rated voltages from 500 to 1200 V. It is recommended to use the BSC of value about 2-3 times the minimum designed value to avoid overcharging. A decoupling capacitor may be used in addition to mitigate lowfrequency drains on the supply [17,19,20]. e applicable values of the capacitor for a duty cycle of 50% at different frequencies and different duties at a frequency of 50 Hz are shown in Figure 1 2.2.2. e Bootstrap Diode and Resistor.…”

“…e first parameter to be considered is the maximum voltage drop that we have to guarantee when the highside switch is in on state. e maximum allowable voltage drop (VBOOT) depends on the minimum gate drive voltage (for the high-side switch) to maintain [19,20].…”