NCV78763
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DIAGNOSTICS
The NCV78763 features a wide range of embedded
diagnostic features. Their description follows. Please also
refer to the previous SPI section for more details.
Diagnostics Description
•Thermal Warning: this mechanism detects a
user−programmable junction temperature which is in
principle close, but lower, to the chip maximum
allowed, thus providing the information that some
action (power de−rating) is required to prevent
overheating that would cause Thermal Shutdown. A
typical power de−rating technique consists in reducing
the output dimming duty cycle in function of the
temperature: the higher the temperature above the
thermal warning, the lower the duty cycle. The thermal
warning flag (TW) is given in STATUS register 02 and
is latched. At power up the default thermal warning
threshold is typically 159°C (SPI code 179).
•Thermal Shutdown: this safety mechanism intends to
protect the device from damage caused by overheating,
by disabling the booster and both buck channels, main
sources of power dissipation. The diagnostic is
displayed per means of the TSD bit in STATUS 02
(latched). Once occurred, the thermal shutdown
condition is automatically exited when the temperature
falls below the thermal warning level. The TSD flag is
instead latched and cleared by SPI reading. The
application thermal design should be made as such to
avoid the thermal shutdown in the worst case
conditions. The thermal shutdown level is not user
programmable and factory trimmed (see ADC_TSD in
Table 10).
•SPI Error: in case of SPI communication errors the
SPIERR bit in STATUS 02 is set. The bit is latched. For
more details, please refer to section “SPI protocol:
framing and parity error”.
•Open LEDx string: individual open LED diagnostic
flags indicate whether the “x” string is detected open.
The detection is based on a counter overflow of typical
50μs when the related channel is activated. Both
OPENLED1 and OPENLED2 flags (latched) are
contained in STATUS 01. Please note that the open
detection does not disable the buck channel(s).
•Short LEDx string: a short circuit detection is
available independently for each LED channel per
means of the flag SHORTLEDx (latched, STATUS 01).
The detection is based on the voltage measured at the
VLEDx pins via a dedicated internal comparator: when
the voltage drops below the VLED_LMT minimum
threshold (typical 1.8 V, see Table 15) the related flag is
set. Together with the detection, a fixed TOFF is used.
On NV78763−9 device, TOFF time is terminated
immediately when the inductor current reaches zero.
This improves the dimming behavior via external short
switches (pixel control). Note that the detection is
active also when the LEDx channel is off (in this case
the fixed TOFF does not play any role).
•Overcurrent on Channel x: this diagnostics protects
the LEDx and the buck channel x electronics from
overcurrent. As the overcurrent is detected, the
OCLEDx flag (latched, STATUS 01) is raised and the
related buck channel is disabled. More details about the
detection mechanisms and parameters are given in
section “Buck Overcurrent Protection”.
•Buck Active x: these flags report the actual status of
the buck channels (BUCKACTIVEx, non−latched,
STATUS 01). The MCU can exploit this information in
real time to check whether the channels responded to its
activation commands, or at the contrary, they were for
some reasons disabled.
•Boost Status: the physical activation of the booster is
displayed by the BOOST_STATUS flag (non−latched,
STATUS 01). Please note this is different from the
BOOST_EN control bit, which reports instead the
willing to activate the booster. See also section ”Booster
Enable Control”.
•Boost Overvoltage: an overvoltage is detected by the
booster control circuitry: BOOST_OV flag (latched,
STATUS 01). When VBOOST feedback is lost and too
low voltage is detected on VBOOST pin, overvoltage
will be flagged on NV78763−9 device. More details can
be found in the booster chapter.
•LEDCTRLx pins Status: the actual logic status read at
the LEDCTRLx pin is reported by the flag
LEDCTRLxVAL (non−latched, STATUS 02). Thanks
to this diagnostic, the MCU can double−check the
proper connection to the led driver at PCB level, or
MCU pin stuck.
•Hard Reset: the out of reset condition is reported
through the HWR bit (STATUS 03, latched). This bit is
set only at each Power On Reset (POR) and indicates
the device is ready to operate.
A short summary table of the main diagnostic bits related
to the LED outputs follows.