33797 Datasheet, PDF (20/34 Pages) Freescale Semiconductor, Inc – Four Channel Squib Driver IC

FUNCTIONAL DEVICE OPERATION
OPERATIONAL MODES
TX: Request loop-to-loop short command ($E0–$E3)
RX: Previous executed command information.
TX: Request another command sequence.
RX: Receive loop-to-loop results from test.
CROSS-COUPLED SQUIB IC FUNCTION
The cross-coupled application utilizes the high- and low-
side squib drivers from two different squib driver ICs (see
Figure 9, Cross-Coupled Squib Firing, page 18.) Through the
SPI interface, the squib IC will maintain the capability to
conduct standard diagnostics (short-to-battery, short-to-
ground, short between squibs, and squib diagnostics)
between two different squib ICs. The squib IC must maintain
the capability to fire the squib drivers with the ARM and FIRE
command in either cross-coupled or single IC applications.
When the firing squib driver IC is used in cross-coupled
applications, the low-side squib driver must be activated prior
to activating the high-side squib driver.
Cross-coupling the high- and low-side squib driver from
two different squib driver ICs must be done without interfering
with standard squib operations when the squib IC is used in
an application where the high- and low-side squib drivers are
located on the same IC.
All remaining diagnostic functions will operate standard in
either a cross-coupled or single IC applications. These
functions include R_{R_DIAG}, R_{R_LIMIT_X}, High side, V_{VFIRE_XX},
V_{VFIRE_RTN}, V_TRANSTX, squib current timing measurement,
and FEN_1 and FEN_2 diagnostics.
The SENSE_1A (1B, 2A, or 2B) pin squib IC #1 is
connected to SQB_LO_1A (1B, 2A, or 2B) pin squib driver
IC #2 and is used to feed the diagnostic signal for
determining squib resistance and short-to-battery / ground
conditions (see Figure 9, page 18). During a fire event, the
fire current passes from squib driver IC #1 high-side driver
though the squib to squib driver IC #2 low-side driver. In the
cross-coupled mode, the squib driver IC #2 $C2
(SQUIB_LO_1A_CONT, [1B, 2A, or 2B]) command will be
used to check continuity of the low-side driver from the
SQB_LO_1A (1B, 2A, or 2B) pin to the low-side driver FET.
The low-side driver continuity is checked during the
continuity test. The driver continuity information will be
cleared after the information is transmitted on the next valid
SPI command.
EXAMPLE—CROSS-COUPLED SQUIB COMMAND
SPI SEQUENCE FROM MICROCONTROLLER
TX: Squib IC #1 request squib 1A resistance measurement
($D0).
RX: Previous executed command information.
TX: Run another command on the same squib IC #1.
RX: Receive measured squib 1A resistance information.
TX: Squib IC #1 request continuity command ($C2).
RX: Previous executed command information.
TX: Squib IC #2 request continuity command ($C2).
RX: Previous executed command information.
TX: Squib IC #2 request continuity command ($C2).
RX: Receive low-side driver continuity information for low-
side drivers which reside on IC #2.
TX: Squib IC #1 request another command sequence.
RX: Receive low-side driver continuity information for low-
side drivers that reside on IC #1.
TX: Squib IC #1 request loop-to-loop short command
($E0–$E3)
RX: Previous executed command information.
TX: Squib IC #2 request loop to loop short command for
other ICs ($E8).
RX: Previous executed command information.
TX: Squib IC #2 request loop-to-loop short command for
other ICs ($E8).
RX: Receive loop-to-loop results from test run on IC #1.
TX: Squib IC #1 request another command sequence.
RX: Receive loop-to-loop results from test run on IC #1.
FIRING A SQUIB
The firing of a squib driver requires the FEN_1 and FEN_2
pins to be high and two separate 8-bit writes be made to the
shift register. With FEN_1 pin high, squibs 1A and 1B can be
armed and fired. With FEN_2 pin high, squibs 2A and 2B can
be armed and fired. The first write is to ARM squib drivers in
preparation of receiving the fire command. Squib 1A and
squib 1B can be armed separately from squib 2A and
squib 2B (refer to Table 6) or all squibs can be fired at once
(refer to Table 7). All ARM and 5X (Fire) commands will be
echoed back on the SPI Data output.
33797
20
Analog Integrated Circuit Device Data
Freescale Semiconductor