Multipurpose control ASIC for OMNINET – Data Sheet

AS8401

Rev. A December 1999

Page 4 of 11

Austria Mikro Systeme International AG

1. Automatic mode recognition / mode switching, which is controlled by detection of the driver

voltage VTR related to the source potential:

• Operating as a low side switch (mode1), the driver voltage is approximately 10V and

the point of switching is approximately 25V.

• When the AS8401 operates as a high side switch, during the transition of the OMNIFET

to conduction, provided that the ASIC’s supply voltage, VTR, remains constant, the

ASIC’s output current should be maintained.

2. A bandgap stabilised 5V voltage regulator, which generates the supply voltage for the

digital control section and all the voltage references

3. A floating ground interface to the controlling processor (pin IN), comprised of a reference

current supply and a general current supply, which implements the following functions:

• Generation of a logic voltage signal from the ground-free input current at the pin IN

• In on-state there are further derived currents for the production of the delay and rise/fall

times of the driver from the input current at the pin IN

• After the OMNIFET has been switched off and an additional time delay, the control

ASIC enters power down mode. During power down the current consumption is 80µA

or less. The time delay is necessary to ensure fast comparator operation in order to

complete the power down sequence.

4. A time-delayed power down circuit for the control of the generation of supply current (see

point 4)

5. Voltage delimitation which limits the voltage between gate and source of the OMNIFET to

13V

±1,0V (Protection of the OMNIFET).

The ASIC controls the OMNIFET between gate and source (in particular also when it is used in

high-side-switch applications). The operating condition in which the source potential is more

positive than the gate potential, not permitted for the OMNIFET, is avoided. The use of the

source potential of the OMNIFET as ASIC ground for the ground free coupling between ASIC

and the processor causes fast variable ASIC ground potential during the switching operation

particularly when the AS8401 is used in high side switch applications.

The size of the switching-on pulses and switching-off pulses and thus the rise and fall times

with given gate-source capacities of the OMNIFET can be programmed by an external resis-

possible to adapt the AS8401 to the particular requirements of the OMNIFET (taking into ac-

count gate source capacitance and required delay/transition times) within certain limits (this

adjustment range is not constituent of these Device Specification). This adaptability is limited

by the possible range of the current at the input pin IN.