A low power high-side current sense SAR ADC for automotive applications

Direct current measurement is one of the most important control characteristics for DC-DC converters. This sensitive method is used for current control of converters, which is much faster and more accurate than voltage control. Unfortunately, the sensitivity of the current measurement is also its major drawback. Especially in automotive applications, electromagnetic interference of the increasing number of electrical appliances severely degrade the performance of analog signal processing. Having proven to be more robust and error-prone, digital signal processing has to be preferred. This work presents a universal high-side current measurement at automotive battery voltage levels up to 24 V with direct analog-to-digital (A/D) conversion in a 180 nm technology. The A/D converter has been realized as 9 bit successive-approximation (SAR) ADC, with a sampling rate of 10 MS/s to detect DC-DC converter switching frequencies above 1 MHz. The combined circuit area of 0.2 mm² dissipated less than 2 mA at 1.8 V supply voltage. Simulation results of the extracted layout reflect the transient waveforms of a DC-DC LED driver during continuous and discontinuous conduction mode.