L6370Q(2011) 데이터 시트보기 (PDF) - STMicroelectronics

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L6370Q
(Rev.:2011)

2.5 A single high-side smart power switch

STMicroelectronics 

L6370Q

Circuit description

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 sinked

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 tON interval, the output DMOS is switched

OFF and the DIAG2 goes low, for a time interval tOFF lasting 64 times tON.

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, or, whether not, the normal condition operation is resumed.

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

ranging between 50 pF and 2 nF to have:

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

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 Θlim-ΘH.

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 Vsth1(9 V typ.) and Vsth2 (8.5 V typ.).

Doc ID 022313 Rev 1

11/16

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