VNF9D5F datasheet(14/108 Pages) STMICROELECTRONICS

14 / 108 page

During short circuit condition or medium/hard overload, the output voltage does not overcome current sense shut

down threshold then, the current sense is not operative, the I²t curve is not verified by the implemented algorithm

but the harness protection shall work according to the ILIM_LATCHx setting.

On top of that, the device output current is clamped to the current limitation threshold (ILIMH).

The device behavior in current limitation can be set by a dedicated OTP bit (ILIM_LATCHx) - 1x channel:

•

If ILIM_LATCHx = 1: channel is switched off (after tFILTER_OL) and latched. In order to restart the channel,

the MCU shall reset the latch-off event by refreshing the programmed value in the dedicated register

(CHLOFFTCR0). The action will clear the corresponding CHLOFFSR bit in Output Status Register

OUTSRx and bit 4 in the Global Status Byte.

•

If ILIM_LATCHx = 0: channel is set in auto-restart mode, allowing power limitation.

3.5

Electronic harness protection (STi²Fuse)

The VNF9D5F embeds the STMicroelectronics proprietary I²t functionality, featuring an intelligent circuit breaking

aimed at protecting PCB traces, connectors and wire harness from overheating, with no impact on load transients

like inrush currents and capacitance charging. The electronic wire harness protection, I²t protection, is active in all

operating modes, except in:

•

Standby mode when the device is in the lowest quiescent current consumption mode and all analog and

digital functions are in idle mode and output stages are off. Also, when a channel is in CCM, capacitive

charging mode, the I²t protection on that specific channel is disabled.

•

In CCM mode the wire harness remains in any case fully protected, since CCM mode is the latest aborted

after tCCM_DIS with low RMS current.

•

In LED mode, when the channel is operating in high RDSON and low current limitation mode. In this case,

the wires are protected by the intrinsic thermal I-t capability of the device.

•

In reverse battery condition when outputs are automatically activated.

In all other conditions, the wire harness protection is active and works fully autonomous and in particular does not

require any MCU control or supervision. The I²t protection functionality is equipped with specific safety

mechanism such as built-in self-tests (BIST) for the current sense block responsible for acquiring the load current

and the I²t block itself, which makes this function ASILx ready. In the ITCNTSR register the current value of the

integrated I²t budget is reported and allows the application to monitor how much of the available I²t budget is

actually consumed.

At each POR an internal flag Safe_Restart is set. This flag allows the device to automatically restart after first

harness protection triggering, then the Safe_Restart flag is reset (see Figure 7. I²t counter: single safe restart after

POR with IOUT > INOM ).

Figure 7. I²t counter: single safe restart after POR with IOUT > INOM

I²t counter

COUNTER MAX

SOCR x,

DINx

IOUT

I²t latch

INOM

Safe restart

LATCH

VNF9D5F

Protections

DS13946 - Rev 8

page 14/108

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