PDOC Test Report

Test Date

2024/11/25, William

Purpose

This document outlines the test methods and results to verify the effectiveness of our PDOC system. The system is designed to open the shutdown loop when over-temperature conditions occur on the precharge or discharge resistor. Additionally, the report includes explanations of several circuit operations.

EV5.6.6 Add Clause defining the PDOC (Local Addendum)

PDOC Test Method

In order to simulate the worst-case scenario for the system, we directly connect a 400V DC voltage source (approximately the maximum voltage of the accumulator) to each terminal of our discharge and precharge resistors. Using a thermal camera, we can verify whether the system successfully triggers the shutdown loop to open at the designed temperature. Additionally, it allows us to assess the thermal conductivity of the resistors, heat sink, and thermal paste to ensure effective heat dissipation.

PDOC Test Result

The temperature for triggering the shutdown loop is designed to be 80°C. However, due to the thermal conductivity limitations of the heatsink and thermal paste, it takes some time for the NTC thermistor to respond. In the worst-case scenario, the system may only trip when the resistor's surface temperature reaches 90°C. This is still within safe limits, as the resistor's operating temperature range, according to the datasheet, is -65°C to +175°C.

Core System Explanation

How to Detect The Temperature

In our system, we use an NTC thermistor (Littelfuse KX103J2) with a Beta value of 3892. The Beta value is a critical characteristic that determines the thermistor's resistance at specific temperatures. When paired with a resistor, it forms a voltage divider, which outputs varying voltages corresponding to different temperatures. The following graph illustrates the relationship between temperature and resistance.

To monitor the temperature, a hysteresis OPA comparator is used to determine whether the temperature exceeds 80°C based on the voltage. Additionally, the hysteresis OPA comparator ensures system stability by introducing a hysteresis effect. Once the over-temperature protection is triggered, it will only disengage when the temperature drops back to 70°C, preventing rapid on/off switching and ensuring reliable operation.