NCV7519, NCV7519A
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19
status bits in the device’s status registers. Off−state faults
will simply set the FLTB flag and the channel’s status bits.
Status information is retrieved by SPI read of registers R4
and R5 (Table 11). Status information for each channel is
3−bit priority encoded (Table 12). Shorted load fault has
priority over open load and short to GND. Short to GND has
priority over open load. Priority ensures that the most severe
fault data is available at the next SPI read.
Status is latched for the currently higher priority fault and
is not demoted if a fault of lower priority occurs. The status
registers are reset to “Diagnostic Not Complete” after
reading the registers, or by asserting a reset via RSTB. Status
registers are not affected by ENB.
When either RSTB is low or ENB is high, diagnostics are
disabled. When RSTB is high and ENB is low, open load
diagnostics are enabled according to the state of the
Diagnostic Config 2 register bits R3.D[5:0] (Table 10).
Diagnostic Pulse Mode
The NCV7519 has functionality to perform either
on−state or off−state diagnostic pulses (Table 5). The
function is provided for applications having loads normally
in a continuous on or off state. The diagnostic pulse function
is available for both latch−off and auto−retry modes. The
pulse executes for the selected channel(s) on low−high
transition on CSB.
Diagnostic pulses have priority and are not dependant on
the input (IN
X
, G
X
) or the output (GAT
X
) states. The pulse
does not execute if: ENB =1 (device is disabled); both an ON
and OFF pulse is simultaneously requested for the same
channel; an ON or OFF pulse is requested and a SCB
(shorted load) diagnostic code is present for the selected
channels; an ON or OFF pulse is requested while a pulse is
currently executing in the selected channels (i.e. a blanking
timer is active); the selected channels are currently under
auto−retry control (i.e. refresh timer is active).
When R1.F
X
= 1, the diagnostic OFF pulse command is
executed. The open load diagnostic is turned on if disabled
(see Diagnostic Config 2 − R3), the output changes state for
the programmed t
BL(OFF)
blanking period, and the
diagnostic status is latched if of higher priority than the
previous status. The output assumes the currently
commanded state at the end of the pulse.
When R1.N
X
= 1, the diagnostic ON pulse command is
executed. The output changes state for the programmed
t
BL(ON)
blanking period, and the diagnostic status is latched
if of higher priority than the previous status. The output
assumes the currently commanded state at the end of the
pulse. A flowchart for the diagnostic pulse is given in
Figure 16.
Shorted Load Detection
An external reference voltage applied to the FLTREF
input serves as a common reference for all channels
(Figures 1 and 2). The FLTREF voltage should be within the
range of 0.35 to 2.75 V and can be derived via a voltage
divider between V
CC1
and GND.
Shorted load detection thresholds can be programmed via
SPI in eight increments that are ratiometric to the applied
FLTREF voltage. Separate thresholds can be selected for
each channel via the Diagnostic Config 1 register bits
R2.C[11:9] (Tables 6 and 9).
A shorted load fault is detected when a channel’s DRN
X
feedback is greater than its selected fault reference after
either the turn−on blanking or the filter has timed out.
Shorted Load Fault Disable and Recovery
Shorted load fault disable mode for each channel is
individually SPI programmable via the device’s Gate &
Mode select register bits R0.M[5:0] (Table 4).
When latch−off mode (default) is selected, the
corresponding GAT
X
output is latched off upon detection of
a fault. Recovery from latch−off is performed for all
channels by disabling then re−enabling the device via the
ENB input. Recovery for selected channels is performed by
reading the status registers (R4, R5) for the faulted channels
then executing a diagnostic ON or OFF pulse for the desired
channels.
When auto−retry mode is selected the corresponding
GAT
X
output is turned off upon detection of a fault for the
duration of the fault retry time (t
FR
). When auto−retry is
selected, input changes for turn−on blanking time are
ignored while the retry timer is active. Once active, the timer
will run to completion of the programmed time. The output
will follow the input at the end of the retry interval. The timer
is reset when ENB = 1 or when the mode is changed to
latch−off.
The output is automatically turned back on (if still
commanded on) when the retry time ends. The channel’s
DRN
X
feedback is re−sampled after the turn−on blanking
time. The output will automatically be turned off if a fault is
again detected. This behavior will continue for as long as the
channel is commanded on and the fault persists.
In either mode, a fault may exist at turn−on or may occur
some time afterward. To be detected, the fault must exist
longer than either t
BL(ON)
at turn−on or longer than t
FF(ON)
some time after turn−on. The length of time that a MOSFET
stays on during a shorted load fault is thus limited to either
t
BL(ON)
or t
FF(ON)
.
Recovery Retry Time
A global retry timer is used for auto−retry timing. The first
faulted channel triggers the timer and the full retry time is
guaranteed for that channel. An additional faulted channel
may initially retry immediately after its turn−on blanking
time, but subsequent retries will have the full retry time.
If all channels become faulted, they will become
synchronized to the global retry timer.
