Multipurpose control ASIC for OMNINET – Data Sheet

AS8401

Rev. A December 1999

Page 2 of 11

Austria Mikro Systeme International AG

Key Feature s

• Multipurpose control ASIC for OMNIFET (SGS Thompson intelligent power FET family)

• Contains one channel on-chip

• Applicable in low or high side switch circuits

• Supply voltage range 10V – 60V

• Up to +/- 3V potential difference between system’s digital ground and power ground possi-

ble.

• Current controlled interface

• Provides load circuit surveillance and fault back signal

• Typical rise time shorter then 2.4us

• Typical fall time shorter then 3.8us

• 8 pin SOIC Package

General Descriptio n

The ASIC’s purpose is to drive one OMNIFET n-channel power FET device. (OMNIFET is a

trademark of SGS-THOMSON). The OMNIFET’s integrated protection circuits (current limita-

tion, over temperature protection, ...) are supplied via the OMNIFET’s gate input. Thus in the

OMNIFET’s on-state, a DC gate current of 0.5mA is required. In a failure case (e.g. excessive

temperature) an internal resistor of about 100

Ω is connected between the OMNIFET’s gate

and source. This state is used to detect errors by the controlling ASIC.

The control ASIC’s standard application is in the use as a high side or low side switch (select-

able) in a 24V-supply system, where the functionality is guaranteed up to a maximum driver

voltage of 55V.

In the load dump case (VTR = 60V, Pulse duration about 5ms, 5 pulses) the ASIC remains

functioning (function state A) with modified parameters (rise times and fall times).

The ASIC contains one driver circuit (OMNIFET driver) and realises the following functions:

• Current controlled on switch / off switch with defined rise, fall and delay times (programma-

ble externally at the control input), that is usable as a high side or low side switch.

• Automatic mode change between low side and high side use. This allows processing both,

relatively low driver voltages (up to 25V, low side switch) and high driver voltages (up to

60V, high side switch) by detecting the present driver voltage related to OMNIFET’s source

potential.

• Error detection for the OMNIFET and generation of an error status signal.

• Gate to source voltage limitation for the OMNIFET to a maximum of 13V (OMNIFET pro-

tection).

• Floating ground interface between the controlling processor (control and status signal) and

the driven OMNIFET; provided by separation of digital and power ground. The OMNIFET’s

source potential is the ASIC’s ground.

• Power reduction in the off-state (Supply current falling to less than 80µA after switching the

ASIC off).

The driver can be used as low or high side switch.

The control and the fault back signal are realised with current sources in order to guarantee

the separation of digital ground (of the processor) and power ground (at the load circuit). This

is a safety function for a broken ASIC ground line and it fulfils EMC demands.