VNF9Q20F datasheet(18/111 Pages) STMICROELECTRONICS

18 / 111 page

Figure 9. Protection curve in parallel mode with INOM = 6 A and tNOM = 300 s vs a 0.17 mm2 wire isothermic

curve

The I²t protection curve can be moved in y-direction by changing the INOM value and in x-direction changing the

tNOM value. The following figure represents the total range of I²t the device can cover, ranging from

INOM_MIN = 1.5 A with tNOM_MIN = 1 s up to INOM_MAX = 6 A with tNOM_MAX = 300 s.

Figure 10. Lowest INOM and tNOM (left hand) and highest INOM and tNOM (right hand) configuration setting

100

0.0001

0.001

0.01

0.1

100

1000

time [s]

I²t staircase curve typical

Cable @ 85°C

Note:

In the highest configuration settings, a 0.13 mm2 wire is not protected as the I²t staircase curve intersects with

the isothermic curve of the wire.

The I²t protection curve consists of 13 steps, each of them corresponding to a specific current threshold.

Whenever the load current exceeds a threshold, a counter is counting up. If for instance looking at the example in

Figure 8, the current would exceed the value of INOM = 4 A, but stay below the current threshold of the next step,

which is set at 1.03* INOM about, the counter would reach its threshold value after tNOM = 300 s, the harness

protection is triggered and the output channel is automatically latched off.

Diagnostic about I²t intervention is available through SPI with the ITOFFSRx bit in the OUTSRx output status

harness I²t protection. An additional diagnostic indication is available, depending on the configuration of MCUext

bit in the OTP memory area. The following table explains the functionality of DINx pins depending on the MCUext

bit setting.

VNF9Q20F

Protections

DS13909 - Rev 8

page 18/111

VNF9Q20F Datasheet(PDF) 18 Page - STMicroelectronics