NCV7694
Short to Ground
output diagnostic pin can be connected directly to the Enable
of the DC/DC converter. In case of fault, the DC/DC
converter is automatically disabled after blanking times.
In case of short to ground, huge amount of current is
passing through the LEDs. To protect the LEDs and Human
eyes, the safety mechanism can be implemented. The DIAG
VBAT
VSTRING
VDD_MCU
EN
DC / DC
NCV898031
C1
High LED current
R2
20 kW
VS
VSTR
FLASH = Low
V DET
<
350 mV
DET
FLASH
FLASH
GATE
FB
DIAG
DIAG
RETL
NCV7694
R3
Define
max
R1
RFRL
exposure
time
R4
Define
max
GND
frequency
Figure 7. Short to Ground Detection Circuit
When Short to Ground is introduced during
> V and FLASH is low, the 10 ms blanking
time eliminate the false faults. When blanking time expires,
the NCV7694 immediately report a fault on the DIAG pin
input pin. (The next FLASH pulse will not be propagated to
the output, because the DC/DC converter is not activated).
The microprocessor can distinguish between Short to
GND and Open Load during FLASH = Low. If the DIAG pin
remains low during FLASH = Low, the Short to Ground was
detected and it is not recommended to not turn ON the
V
STRING
STRth
which leads to the switching OFF the V
voltage to
STRING
protect the LEDs. The output GATE pin remains active. The
device is recovered with next rising edge on the FLASH
V
STRING
voltage.
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