3

Protections

3.1

Power limitation

The basic working principle of this protection consists of an indirect measurement of the junction temperature

swing ΔTJ through the direct measurement of the spatial temperature gradient on the device surface in order to

automatically shut off the output MOSFET as soon as ΔTJ exceeds the safety level of ΔTJ_SD. According to the

voltage level on the FaultRST pin, the output MOSFET switches on and cycles with a thermal hysteresis

according to the maximum instantaneous power which can be handled (FaultRST = Low) or remain off (FaultRST

= High). The protection prevents fast thermal transient effects and, consequently, reduces thermo-mechanical

fatigue.

3.2

Thermal shutdown

In case the junction temperature of the device exceeds the maximum allowed threshold (typically 175 °C), it

automatically switches off and the diagnostic indication is triggered. According to the voltage level on the

FaultRST pin, the device switches on again as soon as its junction temperature drops to TR (FaultRST = Low) or

remains off (FaultRST = High).

3.3

Current limitation

The device is equipped with an output current limiter in order to protect the silicon as well as the other

components of the system (for example bonding wires, wiring harness, connectors, loads, etc.) from excessive

current flow. Consequently, in case of short-circuit, overload or during load power-up, the output current is

clamped to a safety level, ILIMH, by operating the output power MOSFET in the active region.

3.4

Negative voltage clamp

In case the device drives inductive load, the output voltage reaches a negative value during turn off. A negative

voltage clamp structure limits the maximum negative voltage to a certain value, VDEMAG, allowing the inductor

energy to be dissipated without damaging the device.

VN9004AJ

Protections

DS12483 - Rev 5

page 21/42