Circuit description L6370
10/18 Doc ID 4282 Rev 8
3.4 Short circuit operation
In order to minimize the power dissipation when the output is shorted to grounded, an
innovative, non dissipative short circuit protection (patent pending) is implemented,
avoiding, thus the intervention of the thermal protection in most cases.
Whenever the output is shorted to ground, or, generally speaking, an overcurrent is sink by
the load, the output devices is driven in linear mode, sourcing the Isc current (typically 3.2 A)
for a time interval (ton) defined by means of the external CON capacitor connected between
the ONDELAY pin and GND. Whether the short circuit crease within the ton interval the
DIAG2 output status is not affected, acting as a programmable diagnostic delay.
This function allow the device to drive a capacitive load or a filament lamp (that exhibits a
very low resistance during the initial heading phase) without the intervention of the
diagnostic. If the short circuit lasts for the whole t
ON
interval, the output DMOS is switched
OFF and the DIAG2 goes low, for a time interval t
OFF
lasting 64 times t
ON
.
At the end of the t
OFF
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 t
ON
interval and the
sequence starts again, or, whether not, the normal condition operation is resumed.
The t
ON
interval can be set to lasts between 64 ms and 2.56 ms for a C
ON
capacitor value
ranging between 50 pF and 2 nF to have:
t
ON
(μs) = 1.28 C
ON
(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
behaviour of the DIAG2 output is, in this situation, showed in the Diagnostic Truth
Table 7 .
3.5 Overtemperature protection (OVT)
If the chip temperature exceeds Qlim (measured in a central position in the chip) the chip
deactivates itself.
The following actions are taken:
all the output stage is switched off;
the signal DIAG2 is activated (active low).
Normal operation is resumed as soon as (typically after some seconds) the chip
temperature monitored goes back below Θ
lim
-Θ
H
.
The different thresholds with hysteretic behavior assure that no intermittent conditions 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
considered to be 24 V.
In this range the device operates correctly. Below 9.5 V the overall system has to be
considered not reliable.
Protection will thus shut off the output whenever the supply voltage falls below the mask
fixed by the V
sth1
(9 V typ.) and V
sth2
(8.5 V typ.).
