VNF9D5F datasheet(15/108 Pages) STMICROELECTRONICS

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The I²t protection is based on a continuous RMS output current calculation. The current sense for I²t calculation is

sampled for each channel every t_ I²t _SAMPLE (given by the internal base frequency for I²t state machine fCLK)

with linearity ensured up to ILIMH. Since the current sense block is not active in the hard short circuit condition or

whenever the output voltage drops below the current sense shutdown threshold (VOUT_FSD), the behavior of the

channel when in current limitation is programmable (see Section 3.4: Overload protection–Output current

limitation (ILIMH)).

In the case ILIM_LATCHx is programmed in latch-off mode, the current sense, and consequently the I²t protection

function are always active when output is on (for the exceptions see above).

In case ILIM_LATCHx is programmed in auto restart mode, the current sense, and consequently the I²t protection

function are active as long as the output voltage remains above the current sense shutdown threshold

(VOUT_FSD). As soon as the output voltage drops below the current sense shutdown threshold (VOUT_FSD), for

example through a hard short circuit, the current sense is inhibited. In such condition however the I²t wire harness

protection is still operative, integrating with the fastest counter speed, while RMS current is maintained at a low

value, thanks to the power limitation protection, hence still effectively protecting the wire.

The shape of the actual I²t protection curve is a staircase curve, which is determined by two configurable

parameters, I_NOM and t_NOM. Both parameters are accessible through the SPI FSITCRx register, read-and

writeable.

Nominal time tNOM

The default tNOM parameter is programmed by 3 OTP bits (TNOM0, TNOM1, TNOM2, for each channel).

Its default value is 300 s.

Table 9. Nominal time

Nominal time value

TNOM2

TNOM1

TNOM0

300 s (default)

257 s

214 s

172 s

129 s

86 s

44 s

1 s

Nominal current INOM

The default INOM parameter is programmed by 3 OTP bits (INOM0, INOM1, INOM2, for each channel).

Its default value is 15 A.

Table 10. Nominal current

Nominal current value

INOM2

INOM1

INOM0

4 A

6 A

7.5 A

9 A

10 A

11.5 A

13 A

15 A (default)

VNF9D5F

Protections

DS13946 - Rev 8

page 15/108

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