33797 Datasheet, PDF (27/34 Pages) Freescale Semiconductor, Inc – Four Channel Squib Driver IC

FUNCTIONAL DEVICE OPERATION
PROTECTION AND DIAGNOSIS FEATURES
Internal window comparators will monitor the voltage
difference between the VDIAG_X pin and the VFIRE_XX pin,
and will provide two bits of data to indicate if the pin voltage
is either above (open) or below (shorted) the threshold levels.
When using a high-side safing sensor, typical 5.1 kΩ
reference resistor must be placed across the sensor to
provide a current path for the diagnostic circuit. As long as
there is a current path and the safing sensor switch is open,
the resulting differential voltage will fall between the
comparator thresholds so that neither an open fault nor a
shorted fault condition will be indicated. A closed safing
sensor will be indicated as a short, and a loss of the
connection between the VDIAG_X pin and the VFIRE_XX pin
will be indicated as an open. Any external capacitance on the
VFIRE_XX pin will affect the time needed to settle to an
accurate value.
HIGH-SIDE SAFING SENSOR DIAGNOSTIC DATA
RESULTS
If the VFIRE_XX pin is shorted to the VDIAG_X pin, the
RSSLO bit will be set to “1” and the RSSHI bit will be set to
“1”. If the VFIRE_XX pin has no connection to the VDIAG_X
pin, the RSSLO bit will be set to “0” and the RSSHI bit will be
set to “0”. Standard operation with a safing sensor resistor will
have the RSSHI bit set to “1” and the RSSLO bit set to “0”.
FIRING SUPPLY VOLTAGE (VDIAG_X)
DIAGNOSTICS ($C0 COMMAND)
This function monitors the voltage on the VDIAG_X pin.
The supply voltage is compared to two thresholds (nominal
and minimum) and will provide two bits of data to indicate if
the pin voltage is above, below, or in between the
predetermined threshold levels. There is one diagnostic
circuit for each VDIAG_X pin.
VDIAG_X SUPPLY VOLTAGE DIAGNOSTIC DATA
RESULTS
If the VDIAG_X voltage is above the high limit, bits VDHI
and VDLO will both be set to “1”. If the VDIAG_X voltage is
between the high limit and the low limit, bit VDHI will be set to
“0” and VDLO will be set to “1”. If the VDIAG_X voltage is
below the low limit, bits VDHI and VDLO will both be set to
“0”.
FIRING SUPPLY VOLTAGE (VFIRE_XX)
DIAGNOSTICS ($C5 COMMAND)
This function monitors the voltage on the VFIRE_XX pin.
The supply voltage is compared to two thresholds (nominal
and minimum) and will provide two bits of data to indicate if
the pin voltage is above, below, or in between the
predetermined threshold levels. There is one diagnostic
circuit for each VFIRE_XX pin.
VFIRE_XX SUPPLY VOLTAGE DIAGNOSTIC DATA
RESULTS
If the VFIRE_XX voltage is above the high limit, bits VFHI
and VFLO will both be set to “1”. If the VFIRE_XX voltage is
between the high limit and the low limit, bit VFHI will be set to
“0” and VFLO will be set to “1”. If the VFIRE_XX voltage is
below the low limit, bits VFHI and VFLO will both be set to “0”.
FIRING SUPPLY VOLTAGE DIAGNOSTICS,
VDIAG_X V1, V2, V3, V4 ($C6 COMMAND)
The VDIAG_X V1, V2, V3, V4 function monitors voltage on
the VDIAG pins. The voltage being measured is then
compared to four thresholds and will provide four bits of data
to indicate if the pin voltage is above, below, or between the
predetermined threshold levels. There is one diagnostic
circuit for each VDIAG_X pin.
VDIAG_X VOLTAGE DIAGNOSTIC DATA RESULTS
If the VDIAG_X voltage is above the threshold limit, the
VDIAG_X VX bit will be set to “1”. If the VDIAG_X voltage is
below the threshold limit, the VDIAG_X VX bit will be set to
“0”.
VFIRE_RTN DIAGNOSTICS ($C9 COMMAND)
This function monitors the resistance on the VFIRE_RTN
pin for open pin connections. The VFIRE_RTN voltage is
compared to a threshold to determine if the VFIRE_RTN pin
connection between the pin and the printed circuit board is
shorted or open.
VFIRE_RTN DIAGNOSTIC DATA RESULTS
If the VFIRE_RTN pin is above the threshold limit (open),
the VFIRE_RTN X VFXLOW will be set to “1”. If the
VFIRE_RTN pin is below the threshold limit (shorted), the
VFIRE_RTN X VFXLOW will be set to “0”.
VFIRE return tests are disabled during firing.
DESIGN NOTES
For all standard or cross-coupled squib IC configurations,
the SQB_LO_XX pin must be tied to a SENSE_XX pin for
either squib IC #1 or squib IC #2 (see Figure 6 and Figure 9).
An active 600 µA current sink is located in the SENSE_XX
pin. The sink current is used to pull the charge off the external
EMC / filter caps after a diagnostic measurement has been
made.
SQUIB SHORT-TO-BATTERY / GROUND
DIAGNOSTICS ($C1 COMMAND)
This function monitors the voltage on the SENSE_XX pins.
The voltage is compared to two thresholds (minimum and
maximum) and will provide two bits of data to indicate if the
pin voltage is above, below, or in between the predetermined
threshold levels.
When enabled, a 2.7 mA current source located in the
SQB_HI_XX pin is activated, sourcing current from the
Analog Integrated Circuit Device Data
Freescale Semiconductor
33797
27