Configurable and Scalable High-Side or Low-Side Driver in BiCMOS with 20dBµV Emission at 88MHz

Abstract

System Basis Chips (SBC) demand configurable High Side (HS) or Low Side (LS) drivers for driving Light Emitting Diodes (LEDs) in HS or LS configuration. LS configuration is also used to create DC shift for instrumentation amplifiers for precision offset measurements. Instead of independent drivers for each configuration, a driver configurable for both HS and LS topologies with accurate current sensing is preferred. In this paper, a 40V slew rate controlled, configurable HS or LS driver with accurate current sensing to provide load current information and current limitation for automotive applications is presented. One of the challenges is to have precise current sensing of voltages as low as 2mV. Existing solutions use auto zeroing or chopper techniques. A simple and cost effective solution using NPN transistors in BiCMOS process is proposed. This simplifies the design of the driver for both HS and LS configurations and the freewheeling concept for inductive loads without adding external Schottky diodes. The switch drives 90mA load current with 300mV Drain-Source drop voltage. The slew rate is 220mV/µs with a conducted emission of 20dBµV at FM band of 88MHz. The current limit is 130mA with 100mA over current detection threshold.