33797 datasheet(21/34 Pages) FREESCALE

21 / 34 page

Analog Integrated Circuit Device Data

Freescale Semiconductor

33797

FUNCTIONAL DEVICE OPERATION

OPERATIONAL MODES

The second write is to actually fire the desired driver. The

four most significant bits of the second write are used to

establish a parity with the four most significant bits of the first

write. The four least significant bits are the data bits, and

each bit represents a squib driver or squib driver pair. If there

is a parity mismatch of the four most significant bits, the data

bits will be ignored and the squib drivers will not have their

status changed. The 2-byte write sequence must then be

started again. During the first write, when the drivers are

armed, all diagnostic functions are cleared.

Once fired, a driver can only be turned off by one of the

following:

• Sending a valid 2-byte write sequence through the shift

• Having the reset pin pulled low.

• Having the thermal shutdown limit exceeded (once

minimum firing duration requirement has been met;

refer to Note 4 in the Maximum Ratings table, page 5).

• Having the FEN pin pulled low. Note that the code

sequences allow any combination of drivers to be

turned on or off.

Once fired, the current limit measurement register

increments when the squib current is measured and is above

the IMEAS threshold during the timer activation.

The FEN_1 or FEN_2 pin must be high to enable firing of

the drivers. If fire command is active and the FEN (1 or 2) pin

is pulled low, the FET drivers will turn off (assuming the latch

and hold function is not in effect; refer to paragraph entitled

FEN_1 and FEN_2, page 29). If fire command is active and

the FEN (1 or 2) pin is pulled high, the FET driver will turn on.

During the firing of a squib, significant I•R losses may

occur, which could cause a voltage shift across a circuit

board trace. It is recommended that current paths for

discharging the firing supply storage capacitors through the

squib be kept as short as possible and isolated from logic and

diagnostic grounds.

Table 6. Squib Firing Commands

Hex Code

Command Description

A0 ARM Squib Drivers 1A and 1B

A1 ARM Squib Drivers 2A and 2B

Byte #1

Byte #2

Squib B

High Side

Squib B

Low Side

Squib A

High Side

Squib A

Low Side

Squib 2B

Squib 2A

Squib 1B

Squib A1

ARM Squib Drivers 1A and 1B

ARM Squib Drivers 2A and 2B

ARM Squib Drivers 1A, 1B, 2A, 2B

OFF

33797 Datasheet(PDF) 21 Page - Freescale Semiconductor, Inc

33797 Datasheet(HTML) 21 Page - Freescale Semiconductor, Inc

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34

Datasheet Download

Link URL