33797 datasheet(17/34 Pages) FREESCALE

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Analog Integrated Circuit Device Data

Freescale Semiconductor

33797

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.

33797 Datasheet(PDF) 17 Page - Freescale Semiconductor, Inc

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