L6370Q datasheet(12/17 Pages) STMICROELECTRONICS

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Circuit description

L6370Q

12/17

DocID022313 Rev 2

3.4

Short-circuit operation

In order to minimize the power dissipation when the output is shorted-to-ground, an

innovative, non-dissipative short-circuit protection (patent pending) is implemented,

avoiding the thermal protection.

Whenever the output is shorted-to-ground, or, an overcurrent is sinked by the load, the

output devices are driven to linear mode, sourcing the Isc current (3.2 A typ.) for a time

interval (tON) defined by the external CON capacitor connected between the ON-DELAY pin

and GND. If the short-circuit increases within the tON interval the DIAG2 output status is not

affected, acting as a programmable diagnostic delay.

This function allows the device to drive a capacitive load or a filament lamp (that exhibits a

very low resistance during the initial heading phase) without the diagnostic. If the short-

circuit lasts for the whole tON interval, the output DMOS is switched off and the DIAG2 goes

low, for a time interval tOFF lasting tON 64 times.

At the end of the tOFF interval if the short-circuit condition is still present, the output DMOS is

turned on (and the DIAG2 goes high - see Figure 7) for another tON interval and the

sequence starts again, otherwise, the normal condition operation is resumed.

The tON interval can be set to last between 64 ms and 2.56 ms for a CON capacitor value

ranging between 50 pF and 2 nF:

Equation 1

tON (μs) = 1.28 CON (pF)

If the ON-DELAY pin is grounded, the non-dissipative short-circuit protection is disabled and

the Isc current is delivered until the overtemperature protection shuts the device off. The

behavior of the DIAG2 output is, in this situation, showed in Table 7.

3.5

Overtemperature protection (OVT)

If the chip temperature exceeds

Θlim (measured in a central position in the chip) the chip

deactivates itself.

The following actions are taken:

•

the output stage is switched off

•

the signal DIAG2 is activated (active low)

Normal operation is resumed as soon as (after some seconds) the chip temperature

monitored goes back below

Θlim-Θth.

The different thresholds with hysteretic behavior assure that any intermittent condition can

be generated.

3.6

Undervoltage protection (UV)

The supply voltage is expected to range from 9.5 V to 35 V, even if its reference value is 24

In this range, the device operates correctly. Below 9.5 V the overall system is not reliable.

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