Wolfspeed SpeedVal MOD-MB-3P-0900V-40A Series User Manual page 52

Three-phase motherboard

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type 2 event, since the MOSFET is already on and the blanking time has expired, the short-circuit detection can

happen more quickly as the initial delay is no longer present.

A type 1 short circuit can be tested on either the high- or low-side MOSFET. To test the low-side device, connect

a shorting wire between the switch node terminal and the positive DC bus terminal using a 14 AWG wire or larger

as shown in Figure 42. The length of this wire can be adjusted to provide different amounts of inductance in the

short circuit to represent the expected condition in the application.

Figure 42: Shorting wire and Rogowski coil to measure short-circuit current

Then apply a single 5 V pulse to the low-side PWM input to gate the low-side device. It is recommended to start

the testing with a 500 ns pulse, and gradually increase in increments of 100 ns while observing the short-circuit

behavior. Apply only one pulse at a time, and then allow the device to cool for at least 30 seconds before testing

again. As the commanded pulse width is increased above the gate driver's short-circuit protection time, the

gate driver will respond and turn the device off. This timing depends on the gate driver's daughter card. Refer

to the user guide for the gate driver card for more details and how to adjust the timing. In most applications,

the total duration of the short-circuit current (starting at 0 A and returning to 0 A) should be approximately 1us.

This duration is a good balance to avoid false tripping while providing robust short-circuit protection. If the

gate driver is not responding within this time, adjust the settings on the gate driver card to reduce the response

time or increase the turn-off gate drive strength.

PRD-08611 REV. 1, June 2024

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MOD-MB-3P-0900V-40A SpeedVal™ Kit Three-Phase Motherboard User Guide

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