The Electronic Timing Interface provide signals to the spark

module from the micro-processor. The interface requires four

input data signals, and provides four output control chan-

nels.

The interface also provides one output channel for diagnos-

tic information for any open or shorted loads on S1 to S4.

The RESET pin has an internal pull-up resistor to V

cally 100K

Ω, and the ENB pin has an internal pull-down re-

sistor to ground of typically 100K

Ω.

To put the outputs into the TRI-STATE mode at power-on,

the RESET pin should be held low until V

This can be accomplished by micro-processor control, or by

adding a capacitor from the RESET pin to ground.

The RESET pin is used to disable the spark driver outputs by

putting them in a TRI-STATE mode. While in the TRI-STATE

mode the Open Output Fault detection circuitry is active. An

open Output is detected by forcing a small current (I

through the outputs to the loads, and monitoring the voltage

on the output pins rises above the Output Fault Threshold

Voltage (V

is to detect an open wire condition, and not necessarily to

detect a local resistance threshold.

Note that if any output has a Short to battery fault, the fault

pin will go low during this TRI-STATE mode. The internal

comparator is unable to discern why an output pin may be

above the Fault Threshold Voltage, only that it is. In any

case, a fault is reported, even if it is not the anticipated fault.

The TRI-STATE mode is a latched condition. For the outputs

to come out of the TRI-STATE mode, the RESET pin must be

high, and then the data input pin D0 must toggle from a low

state to a high state. The state of the outputs will now be set

by the data inputs D0 and D1, and the ENB input. If ENB is

low when the TRI-STATE mode is cleared, all of the outputs

will go low.

Pins D0 and D1 are used select an output, and ENB will en-

able the selected output. The outputs have have active pull

up to S_HI, and the active pull down to Ground. The default

not enabled output conditions is low, and the enabled output

condition is high. Only one output can be enabled (high) at a

time. The outputs are not latched in any state and will follow

the input selected with D0 and D1 as long as ENB is high.

The detection of an output shorted to ground, or battery, is

dependent on the status of ENB. While ENB is logical 0, all

of the outputs are forced low and the Short to Battery fault

detection circuitry is active. A Short to Battery is detected by

monitoring the voltage on the output pins. If the voltage on

any output pin is above the Fault Threshold Voltage (V

the FAULT pin will go low. The output current sink is limited

to typically 8mA. The short to battery condition must be able

to provide enough current to overcome the current limit and

raise the output pin voltage above the V

When ENB is logical 1, the selected output will be high and

the Short to Ground detection circuitry is active. A Short to

Ground is detected by monitoring the voltage on the output

pins. If the voltage on the selected output pin is below the

Fault Threshold Voltage (V

The output current source is from S_HI limited to typically

25mA to 50mA across the S_HI voltage range. The short to

ground condition must be allow enough resistance to allow

the output pin voltage to fall below the V

the output sourcing short circuit current. Typically, a short to

ground which has 100 Ohms of resistance, or more, can not

be reliably detected. Typically, a short to ground of 20 Ohms,

or less, can be reliably detected across the entire S_HI volt-

age range and device operating temperature range. Note

that if any output has a Short to Battery fault, a Short to

Electronic Timing Interface

Inputs

Output

RESET

ENB

D0

D1

S1

S2

S3

S4

0

X

X

X

Tri

Tri

Tri

Tri

10

X

X

LLLL

1100

H

LLL

1110L

H

L

L

1101LL

H

L

1111LLL

H

FIGURE 14. Truth Table for Electronic Timing Interface

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