33797 datasheet(20/34 Pages) FREESCALE

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Analog Integrated Circuit Device Data

Freescale Semiconductor

33797

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 RR_DIAG, RR_LIMIT_X, High side, VVFIRE_XX,

VVFIRE_RTN, VTRANSTX, 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 Datasheet(PDF) 20 Page - Freescale Semiconductor, Inc

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