A Versatile ±25-A Shunt-Based Current Sensor With ±0.25% Gain Error From −40 °C to 85 °C

This article presents a versatile shunt-based current sensor for battery management applications. It digitizes the current-induced voltage drop across an external shunt resistor with the help of a 2nd-order delta-sigma (
$\Delta \Sigma $
) ADC, whose summing node is implemented as a low-noise capacitively coupled amplifier. To compensate for the shunt’s finite temperature coefficient (TC), the TC of the ADC on-chip voltage reference can be tuned. As a result, the sensor maintains high accuracy when used with low-cost high TC shunts, such as PCB traces, as well as with more expensive low TC shunts, such as metal-alloy resistors. Optimal gain flatness over temperature is achieved by a two-current room-temperature TC tuning scheme, which exploits the shunt’s self-heating at high current levels. Fabricated in a standard 0.18-
$\mu \text{m}$
CMOS process, the current sensor occupies 0.36 mm2 and draws 265
$\mu \text{A}$
from a 1.8-V supply. Over the industrial temperature range (−40 °C to 85 °C) and a ±25-A current range, it achieves the state-of-the-art gain error (±0.25%) with both PCB (1.6
$\text{m}\Omega $
) and metal-alloy (2
$\text{m}\Omega $
) shunts. With these shunts, it achieves 5.3-mA/4.3-mA (rms) resolution in a 10-kHz bandwidth.