L9347

Functional Description

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Functional Description

3.1

Overview

The L9347 is designed to drive inductive loads (relays, electromagnetic valves) in low side

configuration. Integrated active Zener-clamp (for channel1 and 2) or free wheeling diodes

(for channel 3 and 4) allow the recirculation of the inductive loads. All four channels are

monitored with a status output. All wiring to the loads and supply pins of the device are

controlled. The device is self-protected against short circuit at the outputs and

overtemperature. For each channel one independent push-pull status output is used for a

parallel diagnostic function.

Channel 3 and 4 work as current regulator. A PWM signal on the input defines the target

output current. The output current is controlled through the output PWM of the power stage.

The regulator limits of 10% or 90% are detected and monitored with the status signal. The

current is measured during recirculation phase of the load.

A test mode compares the differences between the two regulators. This “drift” test compares

the output PWM of the regulators. By this feature a drift of the load during lifetime can be

detected.

3.2

Input circuits

The INput, CLK, TEST and ENable inputs, are active high, consist of Schmidt triggers with

hysteresis. All inputs are connected to pull-down current sources.

3.3

Output stages (not regulated) Channel 1 and 2

The two power outputs (5A) consist of DMOS power transistors with open drain output. The

output stages are protected against short circuit. Via integrated Zener clamp diodes the

overvoltage of the inductive loads due to recirculation are clamped to typ. 52V for fast shut

off of the valves. Parallel to the DMOS transistors there are internal pull-down current

sources. They are provided to assure an open load condition in the OFF state. With EN=low

this current source is switched off, but the open load comparator is still active.

3.4

Current regulator stages Channel 3 and 4

The current-regulator channels are designed to drive inductive loads. The target value of the

current is given by the duty cycle (DC) of the 2kHz PWM input signal. The following figure

shows the relation between the input PWM and the output current and the specified

accuracy.