33797 Datasheet, PDF (17/34 Pages) Freescale Semiconductor, Inc – Four Channel Squib Driver IC

FUNCTIONAL DESCRIPTION
FUNCTIONAL PIN DESCRIPTION
SQUIB SENSE XX (SENSE_XX)
The Sense pins are used exclusively for diagnostics
related to the squib, driver FETs, or harness. Commands
using the Sense pins include:
• C1, C2, C3, C9
• D<3:0>
• E<3:0>
• E9
• 82/1x
• 83/2x
Independent of the system configuration, normal or cross
coupled, the Sense pin, xx and SquibHi, xx of a single IC are
always connected to the same squib with the SquibHi pin
connected to the high pin of the squib and the Sense pin
connected to the low pin of the squib. A cross coupled
configuration is achieved by only cross coupling the squib low
pins. See Figure 8 and Figure 9.
STANDARD APPLICATIONS
In the standard mode, the $C2 (SQUIB_LO_XX_CONT)
command will be used to check continuity of the low-side
driver from the SQB_LO_XX pin to the high-side driver FET
(see Figure 6).
CROSS-COUPLED APPLICATIONS
Used during cross-coupling applications involving two
four-channel squib driver ICs (squib driver IC #1 and squib
driver IC #2). SENSE_XX pins from squib driver IC #1 are
connected to their respective squib minus pins (Squib Low /
SQB_LO_XX) from squib driver IC #2 (Figure 9).
SENSE_XX pins are used to feed diagnostic signals back to
squib driver IC #1 for determining squib resistance, short-to-
battery/ground, and squib loop-to-loop short conditions.
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 (Figure 9). In the cross-coupled mode, the
squib driver IC #2 $C2 (SQUIB_LO_XX_CONT) command
will be used to check continuity of the low-side driver from the
SQB_LO_XX pin to the low-side driver FET.
DESIGN NOTES
Diagnostics always have the form of a forcing function and
a measurement or sense function. In a cross couple
configuration, most diagnostics are unaffected and are single
commands except for $C2 Low Side FET Continuity and
$E<3:0> Harness Shorts, and 83/2x Low- Side FET test. This
command must be sent to each IC to be executed. For these
three diagnostics, two commands are required because the
forcing function and sensing function are on separate ICs.
Harness Shorts Diagnostics: Force using $E<3:0> on
IC#1, Sense $E8 on IC2
Low-Side FET Continuity: Force using $C1 on IC#1,
Sense using $C2 on IC#2
Low-Side FET Test: Force using $C1 on IC#1, Sense
using $C2 on IC#2
An active 600 µA current sink is located in the SENSE_XX
pin. The sink current is used to pull the charge off of the
external EMC / filter caps after a diagnostic measurement has
been made.
SQUIB HI XX (SQB_HI_XX)
Squib high pins for squibs 1A, 1B, 2A, and 2B. These pins
are connected to the sources of the high-side FET drivers, as
well as the diagnostic circuitry.
SQUIB LOW XX (SQB_LO_XX)
Squib low pins for squibs 1A, 1B, 2A, and 2B. These pins
are connected to the drains of the low-side FET drivers, as
well as the diagnostic circuitry.
SQUIB FIRING SUPPLY XX (VFIRE_XX)
Firing supply pins for squibs 1A, 1B, 2A, and 2B. These
pins are connected to the drains of the high-side FET drivers.
Feedback for high-side safing for squibs 1A and 1B will be
referenced from VFIRE_1A and squibs 2A and 2B from
VFIRE_2A. For high-side safing, VFIRE_1B should be
connected to VFIRE_1A pin and VFIRE_2B to VFIRE_2A
pin.
SQUIB FIRE POWER GROUND (VFIRE_RTN)
Return for squibs 1A, 1B, 2A AND 2B. The pins are tied to
the source pins of both low-side FET drivers, as well as the
diagnostic circuitry. The RTN pins are tied internally.
Analog Integrated Circuit Device Data
Freescale Semiconductor
33797
17