ISO5852S: Which condition will the short circuit be active?

Rayna,

Thanks for your question.

* Section 9.3.4 in the datasheet offers a concise explanation on the DESAT detection conditions, process, and signaling in ISO5852S

* This excellent app note is extremely helpful to understand DESAT internal function and the system mechanism that cause DESAT detection to occur.

A short circuit condition is detected when DESAT pin voltage goes above the threshold of 9V. The threshold is in section 7.9 in datasheet.

DESAT detection in ISO5852S is a technique to detect when a device is leaving saturation region and turn off the gate by STO to prevent damage from VCE overshoot.

By discharging the gate slowly via the well-controlled Soft turn off function in ISO5852S, the potential for VCE overshoot is reduced compared with quickly discharging the gate.

As far as how the DESAT circuit works internally, since you asked about the internal current source: the internal current source charges the blanking capacitor (value as per customer design, 220pF is mentioned in typical application) and is clamped by the diode, but during events that typically show a device (e.g. IGBT) leaving saturation region and going into linear region, this causes the DESAT pin voltage to rise which then exceeds the 9V detection threshold and causes Soft-turn-off procedure and then fault /FLT pin to go low according to specified timing parameters.

After DESAT is detected, further PWM inputs would during a mute period. The soft-turn-off current 130mA starts to pull the gate slowly, after gate reaches ~2V, Miller clamp takes over and pulls the gate hard to VEE2 (-ve supply)

Below are timing diagram and timing parameter from the datasheet:

If you have any further questions, please let us know, we'll be happy to help with those. If this answered your question, let me know by pressing the green button.

Best,

Dimitri