NCV7694
PINS DESCRIPTION
FLASH
Open Load condition, if the when FB voltage will be below
Flash Input pin is compatible with 1.8 V / 2.8 V logic of
the ON Semiconductor image sensors. Internal pull down
resistor is implemented to prevent unwanted switch on.
Based on the R
FLASH time which can be propagated to the output is 6 ms
and minimum T time, which will can be set, is typically
8 ms. The NCV7694 can be used as companion device for
60 Hz camera sensors in full FLASH T range or 120 Hz
with limited T range.
threshold for longer than blanking time. It is not allowed to
put external voltage higher than 0.19 V on the FB pin when
the device is not active. The voltage on the FB pin has to be
below 0.19 V during VS supply ramp up while FLASH
PWM signal is already present.
and R
resistors, the maximum T
ETL
FRL ON
OFF
GATE
The NCV7694 can drive MOSFET transistors with
minimum GATE voltage of 4.5 V. The preferred mosfet
transistor is NVTFS5C478NL.
ON
ON
DIAG
RETL and RFRL
To reduce thermal retina hazard and thermal injury risk of
the cornea, the safety turn−off function is implemented.
Open Drain DIAG pin can be connected with pull up
resistor to MCU which will be informed about a fault in case
of Open Load, Short to V
LEDs. Diagnostic pin can be connected to the Enable pin of
the DC/DC converter. The output V voltage will be
disconnected and user and devices are protected against
damages. The NCV7694 driver can also inform the system
while FLASH pulse is too long or is send too frequent. The
or Short to Ground of the
STRING
External R
and R
resistor defines maximum
ETL
FRL
exposure time and maximum frame rate. The maximum
times are calculated using resistor values of the R and
STRING
ETL
R
FRL
resistors divided by K
or K
coefficients. If the
FRL
ETL
FLASH pulse is permanently HIGH, the output pulse is
being activated only after FRL timer expire and during the
allowed ETL time period.
Open Load and Short circuit detections of the R , R
ETL FRL
timing resistors are reported on the DIAG pin as well as the
Thermal Shutdown Flag and Under Voltage status on the VS
supply.
Short and Open on the RETL and RFRL
To be able detect the defect on the external resistors the
Open Load and Short to Ground detections are implemented
in the NCV7694. If the resistor value will be below 750 W,
short to ground will be detected. If the resistor value
becomes higher than 17.5 kW, Open Load is detected.
As soon as a fault condition is detected, then after a short
filter time the driver is switched off and fault on the DIAG
pin is reported
DET
Detection pin is sensing the voltage at the cathode of the
LEDs. The voltage on DET pin during the FLASH−ON
period should be in range from V
(0.35 V) to V
SGth
SVth
(V
– 1.22 V). Below 0.35 V the device will detect
STRING
Short to ground and above V
will detect Short LEDs to V
minus 1.22 V the device
STRING
.
STRING
In case of DET pin is disconnected, device will go into
fault because internal pull−up to V is implemented.
Short to ground can be detected only when output is not
activated.
VSTRING
STRING
High voltage input pin sense the voltage on the top of the
LEDs and enable the Open Load and Short diagnostic as
soon as the voltage exceed the threshold VSTRth >2.2 V. If
DC/DC converter is not used, the VSTRING voltage has to
be connected to the VS pin. If the LED diagnostic is not
required, then the VSTRING pin has to be grounded.
FB
A feedback loop regulates the current through the external
LEDs. The voltage across the external sense resistor is
regulated to the 300 mV typ. Using FB pin can be detected
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