SPRUJF4 EVM User's guide

SPRUJF4A October 2024 – December 2024

2.1.5 External Overcurrent Protection

The TIEVM-MTR-HVINV implements two redundant overcurrent protection (OCP) circuits. First, an external comparator is capable of reporting an overcurrent fault to the 3-phase inverter. Second, the daughterboard MCU is capable of reporting an overcurrent fault through the use of internal comparators. If either OCP mechanism reports a fault, both the 3-phase inverter and the MCU transition into a fault state. The system remains in a fault state until the state is manually cleared.

Figure 2-12 shows the external OCP circuit. This circuit sums the three current phases, the compares that sum to a reference value. If the summation of the three phase currents ever exceeds the reference value, then the 'IPM_CIN' signal switches and the IPM reports an overcurrent fault to the microcontroller. The exact overcurrent protection current can be calculated by below equations.⁽¹⁾

First, the reference voltage V_- is generated via a voltage divider from the 3.3V power rail.

Equation 7.

V_{-} = 3.3 V \times \frac{R_{108}}{R_{107} + R_{108}} = 3.3 V \times \frac{1 k}{20 k + 1 k} = 0.15714 V

Next, note that the resistance from any IPM phase to the junction point U10₊ is 5.12kΩ. In this scenario, two of the phases (for example, V and W) are at approximately 0A, while the third phase (U) is experiencing a current spike and triggering the OCP circuit. As such, consider R_V and R_w in parallel.

Equation 8.

R_{U} = R_{V} = R_{W} = R_{87} + R_{8} = 5.12 k

Equation 9.

R_{V | | W} = {(\frac{1}{R_{V}} + \frac{1}{R_{W}})}^{- 1} = {(\frac{2}{5.12 k})}^{- 1} = 2.56 k

The voltage at the junction point U10₊ can be referred to as V₊. V₊ is generated via voltage division relative to the voltage of each phase of the IPM (V_U, V_V, V_W). Note that V_V and V_W are both assumed to be 0V in this scenario, as I_V and I_W are both stated to be at or approaching 0A.

Equation 10.

V_{+} = (V_{U} - V_{VW}) \times \frac{R_{V | | W}}{R_{U} + R_{V | | W}} = V_{U} \times \frac{R_{V | | W}}{R_{U} + R_{V | | W}}

Equation 11.

V_{+} = V_{U} \times \frac{R_{V | | W}}{R_{U} + R_{V | | W}} = V_{U} \times \frac{2.56 k}{5.12 k + 2.56 k} = \frac{V_{U}}{3}

V_U is also defined as the Voltage across the shunt resistor R_shunt during the overcurrent event.

Equation 12.

V_{U} = R_{shunt} \times I_{OCP} = 0.05 \times I_{OCP}

For the OCP circuit to trigger, V₊ must be greater than or equal to the reference voltage V_-.

Equation 13.

V_{+} = \frac{0.05 \times I_{OCP}}{3} \geq V_{-}

Equation 14.

I_{ocp} \geq \frac{V_{-}}{(\frac{0.05}{3})} = \frac{0.15714}{(\frac{0.05}{3})} = 9.42857 A

TIEVM-MTR-HVINV External Overcurrent Protection Circuit

Figure 2-12 External Overcurrent Protection Circuit

Certain revisions of the board may have higher OCP limits for the external circuit. In these instances, the internal (CMPSS) protection is still fully functional at the intended levels. Refer to Section 6.1 for more information.