L9348

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1.0 FUNCTIONAL DESCRIPTION

1.1

Overview

The four low-side switches are designed to drive inductive loads (relays, electromagnetic valves). For the 3A

switches (Q3/4) integrated free-wheeling diodes (D3/4) are available and can be used as recirculation path for

inductive loads. If either integrated nor external free-wheeling diodes are used the output voltage is clamped

internally during discharge of inductive loads. The switches are controlled by CMOS compatible inputs (IN1-4)

if the enable input is set to “high”. The status of each switch is monitored by the related status output (ST1-4).

1.2

Input Circuits

The control and enable inputs are active high, featuring switching thresholds with hysteresis and pull-down cur-

rent sources. Not connected inputs are interpreted as “LOW”. If the enable input is set to “LOW” the outputs are

switched off independent of the control input state (IN1-4).

1.3

Switching Stages

The four power outputs consist of DMOS-power transistors. The output stages are protected against short circuit

to supply. Integrated output voltage clamp limits the output voltage in case of inductive load current flyback. In-

ternal pull down current sources are provided at the outputs to assure a defined conditon in OFF mode. They

will be disconnected in the disable mode (ENA=L). If the supply of the device gets lost but the loads and D3/4

are still supplied, an internal pull down resistor discharges the gate of the DMOS-power transistor to avoid

switch on due to capacitive coupling.

1.4

Status Outputs

The CMOS compatible status outputs indicate the state of the drivers (LOW-level indicates driver in OFF state,

HIGH-level indicates driver in ON state). If an error occurs the status output voltage changes like described in

chapter 1.6 Error Detection.

1.5

Protective Circuits

The outputs are protected against current overload, overtemperature, and Power-GND-loss.

1.6

Error Detection

Two main error types are distinguished in the diagnostic logic. If current overload, overtemperature, signal-

GND-loss or a power-GND-loss occurs, the status output signal is inverted, an internal register is set and the

driver is shutdown. The reset is done by switching off the corresponding control input or the enable input for at

All other errors (openload, active output voltage clamp) only cause an inverted status output signal but no shut-

error condition is no longer valid (see Figure 7 and Figure 8).

Excepting the detection of the active output voltage clamp all errors are digitally filtered before they are inter-

preted by the diagnostic logic.

The table 6 below shows the different failure conditions monitored in ON and OFF state:

Table 6.

ON State

ENA = HIGH,

IN = HIGH

OFF State

ENA = HIGH,

IN = LOW

typ. Filter

time

Reset done by

Overloading of output

(also shorted load to supply)

X

18

ENA or INx = “LOW”

for t

Open load

(under voltage detection)

X

44

internal timer (1.5ms typ.)