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 I
sc
current (3.2 A typ.) for a time
interval (t
ON
) defined by the external C
ON
capacitor connected between the ON-DELAY pin
and GND. If the short-circuit increases within the t
ON
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 t
ON
interval, the output DMOS is switched off and the DIAG2 goes
low, for a time interval t
OFF
lasting t
ON
64 times.
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, otherwise, the normal condition operation is resumed.
The t
ON
interval can be set to last between 64 ms and 2.56 ms for a C
ON
capacitor value
ranging between 50 pF and 2 nF:
Equation 1
t
ON
(
μ
s) = 1.28 C
ON
(pF)
If the ON-DELAY pin is grounded, the non-dissipative short-circuit protection is disabled and
the I
sc
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 Overtemperatur
e
protection (OVT)
If the chip temperature exceeds
Θ
lim
(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 Θ
lim
-Θ
th
.
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
V.
In this range, the device operates correctly. Below 9.5 V the overall system is not reliable.
