33813 Datasheet, PDF (41/54 Pages) Freescale Semiconductor, Inc – One Cylinder Small Engine Control IC

The inrush delay bit, in the SPI configuration register for each output, when set to a one(1), will prevent the over-current fault bit
from being set and the over-current protection from shutting off the output for t_INRUSH time rather than t_SC.
Table 20. Inrush Delay Bit
Inrush Delay Bit
0
1
Timer Value
t_SC
t_INRUSH
5.3.7.5 Temperature Limit (OT) Protection
The second protection scheme works by sensing the local temperature of the individual output device. During an over-current
event, the device enters current limit and will remain in current limit until the output driver maximum temperature limit is exceeded
(OT). At this point, the device will shutdown automatically, regardless of the input state. The output will try to turn on again only
when the junction temperature falls below the maximum temperature minus the T_LIM hysteresis temperature value and the input
state is commanding the output to be on. The T_LIM hysteresis value is specified in the static parameter table.
The temperature limit (T_LIM) protection is independent of the over-current protection and is not controlled by the SPI. T_LIM is
always enabled and is always a retry operation.
Outputs may be used in parallel to drive higher current loads provided the turn-off energy of the load does not exceed the energy
rating of a single output driver.
5.3.7.6 Output Driver Diagnostics
Over-current (OC), temperature limit (OT) exceeded, short to ground (SG), and open load (OL) conditions are reported through
the status register for each driver (no SG for the tachometer). Only open load and over-current are reported for pre-drivers. There
is also a bit in the SPI status register to indicate when any of the LSDs or pre-drivers are reporting a fault and when a particular
output has any of the four possible fault conditions present. This makes it easy for the MCU to poll for fault conditions by looking
for a single bit in one register to detect the presence of any fault in the circuit.
5.3.7.7 Open Load Pull-down Current Enable/Disable Bit
An open load condition is detected by the voltage level on the drain of the MOSFET in the off state. Internal to the device is a
pull-down current sink. In the event of an open load the drain voltage is pulled low by the current sink. When the voltage crosses
the open load threshold value, an open load condition is reported. This current sink may be disabled by clearing the appropriate
bit in the in the LSD configuration register. When the current sink is disabled, the off-state open load fault status bit will be forced
to a logic 0.
5.3.7.8 Open Load and Short to Battery Strategy
The injectors, lamps, relays, and tachometer low side outputs are capable of detecting an open load in the off state and short to
battery condition in the on state. All faults are reported through the SPI status register communication. For open load detection,
a current source is placed between the MOSFET drain pin and ground of the IC. An open load fault is reported when the drain
voltage is less than the listed threshold. Open load fault detect threshold is set internally to the listed threshold and may not be
programmed. A shorted load fault is reported when the drain pin voltage is greater than the programmed short threshold voltage
when the device is in the on state.
The open load and short to battery fault threshold voltage is fixed and cannot be modified via the SPI.
5.3.7.9 Short to Ground Strategy
The Injectors, Lamps, and Relays (but not the Tachometer) low side driver outputs are capable of detecting a short to ground
when the output is turned on by measuring the current flow in the output device and comparing it to a known current value. If a
short to ground is detected it is annunciated via a bit in the appropriate SPI status register.
Analog Integrated Circuit Device Data
Freescale Semiconductor
33813
41