An On-/Off-Time Sensing-Based Load-Adaptive Mode Control of Triple Mode Buck Converter for Implantable Medical Devices

Wireless power transfer (WPT) technology applied to implantable medical devices (IMDs) significantly reduces the need for battery replacement surgery health conditions. This paper presents an on-/off-time sensing-based load-adaptive mode control of triple mode buck converter for implantable medical devices; the converter can adjust the control mode for low power consumption and achieve high power conversion efficiency (PCE) under a small active area. The three modes in the proposed system are the pulse width modulation (PWM), pulse frequency modulation (PFM), and ultra-low power (ULP) modes. The on-time sensor can be used to adjust the system from PWM to PFM modes, and the off-time sensor can be used to adjust the system from PFM to ULP modes. It is fabricated using TSMC 0.18 µm CMOS technology. The input voltage lies in the range 2.2–5.0 V, the output voltage is 1.8 V, and the load current lies in the range 0.05–200 mA (x4000). The experimental results demonstrate the seamless mode transition under the step up/down load transient response. The peak PCE is approximately 94.3% at the 80 mA and the minimum PCE is approximately 65.4% within the load current range.