The existing reference design TIDA-01513 is based on single-point isolation leakage error measurement. However, more and more customers require two-point isolation leakage error detection. Two-point isolation leakage error means leakage errors from both positive terminal and negative terminal of high-voltage battery to chassis ground happen at the same time. It is more common to express the required insulation resistance rather than the leakage current, according to International Standards such as ISO6469-1. The insulation resistance provides the information of the possible amount of leakage current.This document explains how to implement two-point insulation resistance measurements based on the existing TIDA-01513 circuit, and discusses the impact of non-ideal characteristics on measurement accuracy.
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Galvanic isolation is a necessary approach to prevent equipment breakdown and passenger electric shock when there are two distinct grounds of different electrical potentials in EV/ HEVs. Accordingly, isolation leakage measurement is a mandatory means to alert danger and to protect circuits and passengers. Leakage current is the sum of all AC currents from the traction battery to chassis ground through these resistances and impedances. In this way, insulation resistance represents the magnitude of the leakage current as traction battery is regarded as high voltage DC source. Meanwhile, some safety standards require a measurement of insulation resistance instead of leakage current.
TIDA-01513 presents an elaborate concept to realize single-point isolation leakage error measurement. It makes sense to extend TIDA-01513 to two-point insulation resistance measurements with the same hardware circuit topology. In addition, it can also be applied to higher voltage system such as 800 V by replacing appropriate switches and resistors.