33882 Datasheet, PDF (20/27 Pages) Freescale Semiconductor, Inc – Six-Output Low-Side Switch with SPI and Parallel Input Control

FUNCTIONAL DESCRIPTION
FUNCTIONAL PIN DESCRIPTION
When the CS pin of this device is pulled low, the fault status
bits are latched, after which any new fault information is not
part of this serial communication event.
Overvoltage Sensing and Protection
When V_PWR exceeds the Overvoltage Shutdown
Threshold, all channels are shut down. Serial input data and
parallel inputs are ignored. The device resumes normal
operation when the V_PWR voltage drops below the
Overvoltage Shutdown Hysteresis voltage. During
overvoltage shutdown, some faults may appear to report
accurately; however, fault sensing operation is only
guaranteed for battery voltage levels from 9.0 V to 17 V.
Fault Status Monitoring Requirements for Serially
Controlled Outputs, SO Pin
Fault monitoring over the serial channel by the IC requires
a minimal amount of overhead for normal operation. Each
status byte received consists of all logic [0]s when faults are
not present. If any logic [1]s are returned, a communication
error occurred, an output fault occurred, or the MODE pin has
been set low. Upon receiving any logic [1] bits, the IC must
resend the last command, verifying the returned logic [1]s, or
correct any communication error.
A 16-bit SPI transmission with a double command byte to
this 8-bit device allows verification of the command (second
byte returned) in addition to the fault byte (first byte returned).
The command (second) byte returned should mirror the bits
sent unless a communication error occurred, in which case
the command resent should accomplish the correction.
If the returned logic [1] validates, it may indicate a MODE
pin high or a confirmed output fault. If it was a confirmed
output fault, extensive diagnostics could be performed,
determining the fault type, especially if vehicle service is
being performed. If all bits return high and verify such, the IC
must verify sending a logic low to the MODE pin. It should
then resend the command, verifying the MODE pin is at a
logic low level, allowing resumption of a normal operation. If
all logic [1]s are again returned, there is an open SO line, an
open MODE line, or the SPI is not functioning.
If the fault does not verify on the command resend, normal
operation is resumed. The error could be a communication
mistake, a momentary output fault, or a fault condition no
longer sensed due to switching the state of the output. For the
first two cases, normal operation is resumed and the software
continues its normal functions. However, in the third case,
additional commands are required for extensive diagnosis of
the fault type if this information is mandatory.
Extensive Fault Diagnostics
More extensive diagnosis may be required under the
following conditions:
• When the fault type of a confirmed fault is desired, the
following scenarios are possible:
– If MSB-2 to MSB-7 indicates a fault, it is an open
load / short-to-ground fault if the output is OFF when
the fault is reported because only open load / short-
to-ground sensing remains operable while an output
is OFF.
– If the output is ON when the fault is reported, the
fault is a short circuit/short-to-battery if ON open
load detection is not enabled via SPI. If ON open
load detection is enabled, it must be disabled and
the fault status reread. If the fault remains, it is a
short circuit / short-to-battery or it is an open load /
short-to-ground.
– If MSB-0 to MSB-2 indicates a fault, it is an open
load / short-to-ground fault if the output is OFF when
the fault is reported because only open load /short-
to-ground sensing remains operable while an output
is OFF.
– If the output is ON when the fault is reported, the
fault is a short circuit/short-to-battery.
• When a fault did not confirm on resend, the fault could
either be an short circuit /short-to-battery fault, not sensed
when turned OFF; an open load /short-to-ground fault, not
sensed when turned ON; or a corrected communication
error.
To determine if it is an output fault condition, the faulted
output must be turned back to its previous state with a new
command. This command should be sent twice to read the
status after the output is latched in this state, thus
confirming the fault and reporting it again.
Parallel control of outputs is a mode of control, potentially
requiring extensive diagnostics if a fault is reported. This is
because parallel control signals are completely
asynchronous to the serial commands. Status reports for
parallel controlled outputs could require additional
information exchange in software to:
• Avoid status reads when outputs are transitioned, thereby
avoiding fault masking times.
• Obtain the state of a faulted output for determining fault
type (if required).
System Actuator Electrical Characteristics (at Room
Temperature)
All drains should have a 0.01 µF filter capacitor connected
to ground. Any unused output pin should not be energized. A
20 Ω resistor to the battery is required to prevent false open
load reporting. There must also be a maximum of 100 Ω of
resistance from V_PWR to ground, keeping battery-powered
loads OFF when the IC is powered down. However, all loads
should be powered by V_PWR to protect the device from full
transient voltages on the battery voltage.
Power-Up
The device is insensitive to power sequencing for V_PWR
and V_DD, as well as intolerant to latch-up on all I /O pins. Upon
power-up, an internal power-ON reset clears the serial
registers, allowing all outputs to power up in the off-state
when parallel control pins are also low. Although the serial
register is cleared by this power-ON reset, software must still
33882
20
Analog Integrated Circuit Device Data
Freescale Semiconductor