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L6374FP Datasheet(PDF) 5 Page - STMicroelectronics |
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L6374FP Datasheet(HTML) 5 Page - STMicroelectronics |
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5 / 13 page  OVERTEMPERATURE PROTECTION (OVT) If the chip temperature exceeds Th (measured in a central position in the chip) the chip deactivates itself. The following actions are taken: - all the output stages are forced in the ”three state” condition, i.e. are disconnected from the output pins; only the clamping diodes at the outputs remain active; - the signal Diag is activated (active low). Normal operation is resumed as soon as (typically after some seconds) the chip temperature moni- tored goes back below Th -HT. The different upper and lower thresholds with hysteretic behavior, assure that no intermittent conditions can be generated. UNDERVOLTAGE PROTECTION (UV) The supply voltage is expected to range from 11V to 35V, even if its reference value is considered to be 24V. In this range the L6374 operates correctly. Below 10.8V the overall system has to be consid- ered not reliable. Consequently the supply voltage is monitored continuously and a signal, called UV, is internally generated and used. The signal is ”on” as long as the supply voltage does not reach the upper internal threshold of the Vs comparator (called Vsh). The UV signal disap- pears above Vsh. Once the UV signal has been removed, the sup- ply voltage must decrease below the lower threshold (i.e. below Vsh -Hys1) before it is turned on again. The hysteresis Hys1 is provided to prevent inter- mittent operation of the device at low supply volt- ages that may have a superimposed ripple around the average value. The UV signal inhibits the outputs, putting them in three-state, but has no effect on the creation of the reference voltages for the internal compara- tors, nor on the continuous operation of the charge-pump circuits. DIAGNOSTIC LOGIC The situations that are monitored and signalled with the Diag output pin are: - current limit (OVC) in action; there are 8 indi- vidual current limiting circuits, two per each output, i.e. one per every output transistor; they limit the current that can be either sour- ced or sunk from each output, to a typical value of 150mA, equal for all of them; - undervoltage protection (UV); - overtemperature protection (OVP); The diagnostic signal is transmitted via an open drain output (for ease of wired-or connection of several such signals) and a low level represents the presence of at least one of the monitored con- ditions, mentioned above. PROGRAMMABLE DELAY The current limiting circuits can be requested to perform even in absence of a real fault condition, for a short period, if the load is of capacitive na- ture or if it is a filament lamp (that exhibits a very low resistance during the initial heating phase). To avoid the forwarding of misleading, short diag- nostic pulses in coincidence with the intervention of the current limiting circuits when operating on capacitive loads, a delay of about 5 µs is inserted on the signal path, between the ”OR” of the cur- rent limit signals and its use as external diagnostic. It takes about 1 µs to charge (or discharge) by 24V a capacitor of 5nF with a current of 120mA . To implement longer delays (from the intervention of one of the current limiting circuits to the activa- tion of the diagnostic) an external capacitor can be connected between pin C3 and ground (pin C3 is otherwise left open). The delay shall then be determined by the ratio of about 10 pF/ µs, using the value of the capaci- tance connected to the pin. ANALOG INPUTS (I1,I2,I3,I4) The input stage of each channel is a high im- pedence comparator with built-in hysteresis (200mV) for high noise immunity. Each compara- tor has one input connected to all the others and tied to a common pin Ref (Pin 11). If this pin is left floating an internal precise band gap voltage ref- erence (1.25V) is applied, otherwise these inputs can be externally programmed by connecting an external voltage source (from 0 to 5V) and the current on this pin is internally limited to ±20µA. The other input pin of each comparator can swing from -7 to 35V. For this reason it has been implemented the structure shown in Figure 2 and the device can also be used as line receiver. When the input voltage is negative, the current is internally limited by a 15k Ω resistor as shown in Figure 2. High and low input thresholds can be obtained by adding and subtracting half of the hysteresis to the voltage of pin Ref (see Figure 3). Figure 2: Equivalent input circuit L6374 5/13 |
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