L9348
6/13
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
least the time t
D
(defined to 1.5ms typ.). See also
Figure 6
in
chapter 2.0 Timing Diagrams
.
All other errors (openload, active output voltage clamp) only cause an inverted status output signal but no shut-
down of the driver. An internal register is set too, but the reset is triggered automatically after the time t
D
, if the
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
s
ENA or INx = “LOW”
for t
1.5ms (typ.)
Open load
(under voltage detection)
X
44
s
internal timer (1.5ms typ.)
