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 remains 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 (e.g. 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.

VND9012AJ

Protections

DS12727 - Rev 3

page 19/40