L9524C Functional description
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Though in mode 2 (relay mode, serial diagnostic interface protocol) the relay should be
switched permanently the L9524C also expects a PWM signal at the CI pin since the serial
diagnostic interface protocol is synchronized by falling edges of the CI signal (see section
“Diagnostic output”). The relay then is switched on permanently if the off time (time between
rising and falling edge) of the PWM signal is less than t
IO sup
since the relay output
suppresses pulses shorter than t
IO sup
(see section “Relay output”). For the same reason the
relay is switched off permanently if the on time (time between falling and rising edge) of the
PWM signal is less than t
IO sup
. In all other cases the relay is switched according to the
PWM signal at the CI pin.
Figure 6. Control input signal in mode 2 for permanent switch on
In mode 1 (relay mode, go/no-go diagnostic interface protocol) no edges are necessary for
the go/no-go protocol. Therefore the relay is switched on if V
CI
= V
CI on
and it is switched off
if V
CI
= V
CI off
.
4.4 Diagnostic output
The diagnostic output stage of the L9524C (DO pin) consists of a current-limited low-side
switch and a pull-up resistor R
DO
to the VS pin. The voltage level of a logical low signal V
DOL
is given by the drop across the low-side switch and the voltage level of a logical high signal
is equal to V
VS
.
The L9524C is able to detect the following failures (see sections “Supply”, “Current
monitoring”, and “Switch monitoring”):
● open-load (6 glow plugs),
● overcurrent (6 glow plugs, stored until power-down),
● any switch is defect (4 switches),
● supply voltage (V
VS
) is too low (“under voltage”),
● supply voltage (V
VS
) is too high (“over voltage”),
● junction temperature (T
J
) is too high,
● charge pump voltage (V
CP
) is too low (“charge pump under voltage”), and
● battery voltage (V
BAT
) is too low (“battery under voltage”).
V
CI
t
V
CI off
V
CI on
0.6
.
V
VS
0.4
.
V
VS
t
relay
ON
OFF
T
CI
t
IO sup
t
IO sup
t
CI fil
+t
del
