TPD2004F

2006-10-31

5

Functional Description

(1)

2-channel squib drive function

Using independent four-channel inputs, this IC controls two high-side and two low-side switches,

making it possible to drive two squibs directly.

(2)

Squib line short-to-battery, short-to-ground and open-circuit diagnostic function (diagnostic voltage

output)

When the squib is in normal state, by an external diagnostic resistor, the device outputs a voltage

the analog multiplexer, it is possible to diagnose short-to-battery, short-to-ground and open-circuit in

the squib line using a microcomputer. Also, the device contains a shunt circuit to prevent the analog

multiplexer from breaking down when the squib is short-to-battery.

(3)

Squib short diagnostic function (diagnostic voltage output)

A diagnostic current is flowed from the internal constant-current source to the squib and reference

resistor, and the voltage drop in each is amplified by an internal amp whose gain is the same for both.

These voltages are output via the analog multiplexer, so that the squib resistance value can be

diagnosed by a microcomputer. Also, the relative accuracy of the output voltages is guaranteed to be

within ±10%.

(4)

Squib driver MOSFET diagnostic function (diagnostic voltage output)

When the squib driver is turned on while the safing sensor is in normal state, the drain voltage of the

MOSFET is output via the analog multiplexer, making it possible to diagnose the state of the

MOSFET using a microcomputer.

(5)

Diagnostic chip select function

Since the device has a chip select function, the diagnostic control bits can be minimized when the

application circuit is configured with multiple chips. Furthermore, when a chip is not selected, the

diagnostic output pin AO is placed in the high-impedance state; therefore it is possible to diagnose

multiple chips using a 1-channel CPU A/D port. (Ignition operates irrespective of CS.)

(6)

Input INHIBIT function

The purpose of this function is to prevent erroneous ignition due to a fault in the microcomputer or

the system power supply. It allows for ignition to be inhibited by pulling the ENB pin low.