An on-chip soft-start technique of current-mode DC-DC converter for biomedical applications

A compact soft-start technique, with an internal circuitry, is presented for the start-up of current mode DC-DC converters for biomedical applications. Examples of medical applications in DC-DC converters include bio-patch, wireless medical sensor node, RFID applications and medical instruments that must have a high stability. To achieve this, a soft-start circuit is proposed to prevent inrush current and output voltage overshoot, during the start-up of the current mode DC-DC converters. The output of the error amplifier is controlled by a stair-case waveform signal generator during the start-up period. The proposed soft-start circuit is fully integrated on chip for portable and wireless medical devices, so that the external components are not required, leading to a reduction in the PCB space and cost. The new soft-start circuit which is digitally-controlled unlike conventional ones was fabricated in a CMOS 0.35-μm process and occupies an active area of 0.19 mm² with a 3.3 V supply voltage.