33797 Datasheet, PDF (21/34 Pages) Freescale Semiconductor, Inc – Four Channel Squib Driver IC

FUNCTIONAL DEVICE OPERATION
OPERATIONAL MODES
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
A0
ARM Squib Drivers 1A and 1B
A1
ARM Squib Drivers 2A and 2B
A2
ARM Squib Drivers 1A, 1B, 2A, 2B
50
OFF
OFF
OFF
OFF
OFF
OFF
OFF
OFF
51
OFF
OFF
OFF
ON
OFF
OFF
OFF
ON
52
OFF
OFF
ON
OFF
OFF
OFF
ON
OFF
53
OFF
OFF
ON
ON
OFF
OFF
ON
ON
54
OFF
ON
OFF
OFF
OFF
ON
OFF
OFF
55
OFF
ON
OFF
ON
OFF
ON
OFF
ON
56
OFF
ON
ON
OFF
OFF
ON
ON
OFF
57
OFF
ON
ON
ON
OFF
ON
ON
ON
58
ON
OFF
OFF
OFF
ON
OFF
OFF
OFF
59
ON
OFF
OFF
ON
ON
OFF
OFF
ON
5A
ON
OFF
ON
OFF
ON
OFF
ON
OFF
5B
ON
OFF
ON
ON
ON
OFF
ON
ON
5C
ON
ON
OFF
OFF
ON
ON
OFF
OFF
5D
ON
ON
OFF
ON
ON
ON
OFF
ON
5E
ON
ON
ON
OFF
ON
ON
ON
OFF
5F
ON
ON
ON
ON
ON
ON
ON
ON
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
register.
• 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 I_MEAS 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.
Analog Integrated Circuit Device Data
Freescale Semiconductor
33797
21