33797 datasheet(28/34 Pages) FREESCALE

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Analog Integrated Circuit Device Data

Freescale Semiconductor

33797

FUNCTIONAL DEVICE OPERATION

PROTECTION AND DIAGNOSIS FEATURES

SQB_HI_XX to the SENSE_XX pin. When resistive

measurement legs to comparators located in the SENSE_XX

pin are activated, a fault on either side of the squib can be

easily detected. An external current path that causes the

SQB_LO_XX, SQB_HI_XX, or SENSE_XX pin to be pulled

below the minimum threshold, will be indicated as a “Short to

Ground”.

If the SQB_LO_XX, SQB_HI_XX, or SENSE_XX pin has

an external current path that causes the pin to be pulled

above the maximum threshold, a “Short to Battery” will be

indicated.

SQUIB SHORT-TO-BATTERY/GROUND

DIAGNOSTIC DATA RESULTS

If SQB_LO_XX, SQB_HI_XX, or SENSE_XX pin is

shorted to battery, the bit NO_SH_BATT will be set to “0”. If

a SQB_LO_XX, SQB_HI_XX, or SENSE_XX pin is shorted to

ground, the bit NO_SH_GND will be set to “0”. During

standard operation, both NO_SH_BATT and NO_SH_GND

will be set to “1”.

Note This diagnostic circuit uses an internal 2.7 mA

current source connected to the SQB_HI_XX pin as a bias. If

the SQB_LO_XX and SQB_HI_XX pins have any

capacitance (due to discrete capacitors or parasitic loading),

the diagnostic condition will require a settling time based on

the RC time constant.

SQUIB HARNESS SHORT-TO-BATTERY/GROUND

DIAGNOSTICS WITH AN OPEN SQUIB ($C3

COMMAND)

This diagnostic function is to be used with no squib present

(open squib condition) in the wiring harness. For an open

squib condition, the function must monitor the voltage on the

SQB_HI_XX and SQB_LO_XX pins for “Short to Ground”

and “Short to Battery” conditions.

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 pair of opposing N-channel CMOS

transistors are activated, creating roughly a 500

Ω resistance

between the SQB_HI_XX and SQB_LO_XX pins together.

A 2.7 mA current source located in the SQB_HI_XX pin is

activated, sourcing current from the SQB_HI_XX to the

SQB_LO_XX pin to the SENSE_XX pin. When resistive

measurement legs to comparators located in the SENSE_XX

pin are activated, a short to BAT/GND fault can easily be

detected. An external current path that causes the

SQB_LO_XX, SQB_HI_XX, or SENSE_XX pin to be pulled

below the minimum threshold, will be indicated as a “Short-

to-Ground”.

If the SQB_LO_XX, SQB_HI_XX, or SENSE_XX pin has

an external current path that causes the pin to be pulled

above the maximum threshold, a “Short-to-Battery” will be

indicated.

SQUIB SHORT-TO-BATTERY/GROUND

DIAGNOSTIC DATA RESULTS

If SQB_LO_XX, SQB_HI_XX, or SENSE_XX pin is

shorted to battery, the bit OPEN NO_SH_BATT will be set to

“0”. If a SQB_LO_XX, SQB_HI_XX, or SENSE_XX pin is

shorted to Ground, the bit OPEN NO_SH_GND will be set to

“0”. During standard operation, both OPEN NO_SH_BATT

and OPEN NO_SH_GND will be set to “1”.

Notes

1. This diagnostic circuit uses an internal 2.7 mA current

source connected to the SQB_HI_XX pin as a bias. If

the SQB_LO_XX and SQB_HI_XX pins have any

capacitance (due to discrete capacitors or parasitic

loading) the diagnostic condition will require a settling

time based on the RC time constant.

2. With an OPEN NO_SH_GND or OPEN_NO_SH_BATT

indicated, the SQB_HI_XX or SQB_LO_XX line

contains the fault condition. The standard squib short-

to-battery/ground diagnostics ($C1) can be executed

to determine if the fault condition is on the SQB_HI_XX

pin or the SQB_LO_XX pin.

CONTINUITY TEST for the LOW-SIDE DRIVER

SQB_LO_XX CONNECTION ($C2 COMMAND)

(LOW-SIDE DRIVER CONTINUITY STATUS)

Low-side driver continuity is checked during the continuity

test diagnostics. This function is used to check continuity at

the SQB_LO_XX pin connection. When enabled, a 2.0 mA

current source located in the SQB_HI_XX pin is activated

sourcing current from the SQB_HI_XX to the SQB_LO_XX

pin.

For a standard connection, the SQUIB_LO_XX_CON bit

will be set to “1”. With an open circuit connection, the

SQUIB_LO_XX bit will be set to “0”. The driver continuity

information will be cleared after the information is transmitted

on the next valid SPI command.

SQUIB RESISTANCE DIAGNOSTICS ($D0–$D3

COMMAND)

This function monitors squib resistance. When enabled, a

diagnostic current derived from R_DIAG is passed through

the selected squib. The resulting voltage across the squib is

amplified and passed to an 8-bit voltage level detector. The

eight bits of data will indicate if the selected squib has a

resistance value above or below predetermined thresholds.

The value of R_DIAG can be varied to allow the detection

range to be altered. Increasing the value of R_DIAG will

reduce the diagnostic current; thus, a higher squib resistance

will be needed to reach the same RTH points. In the case that

R_DIAG is a short-to-ground, the diagnostic current through

the squib resistance will typically be less than 50 mA.

33797 Datasheet(PDF) 28 Page - Freescale Semiconductor, Inc

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