A 30-nΩ Accuracy Low Power Two-step Ratiometric Shunt Resistance Measurement System Using a Switching Regulator-based Current Generator for Shunt-based Current Sensors

This paper presents a high-precision resistance measurement system for shunt-based current sensors in battery-powered vehicles to calibrate the resistance drift of the shunt resistor (R
_s
) caused by aging. To measure the resistance of a 25 μΩ R
_s
using a 10 Ω reference resistor (R
_REF1
) with a ratio of 400,000:1, we proposed a two-step ratiometric resistance measurement technique using a reference resistor with an intermediate resistance value of 10 mΩ. The ratiometric measurement cancels drift and noise of a test current by synchronously measuring the voltages across the resistors using analog front-end (AFE) circuits. A high-side ratiometric measurement circuit uses a DC test current. A low-side ratiometric measurement circuit uses an AC test current (
I
_E2
) at 162.8 Hz generated by a two-stage switching regulator-based current generator (SRCG) and a lock-in technique to reduce the influence of the thermal electromotive force of the R
_s
. The two-stage SRCG consisting of a charge sampling stage and a switching regulator stage reduces both power consumption and inrush current from the power supply. It operates with a 15.6 kHz switching signal modulated at 162.8 Hz to reduce the size of LC components. The SRCG and AFEs operate synchronously, and all spurious noise is filtered by a 3rd-order CIC filter in a digital domain. The implemented system demonstrates less than 0.12% (30 nΩ) resistance measurement error with a 25 μΩ R
_s
, and the SRCG generating the AC test current of 1 A
_rms
draws 43 mA from the power supply.