Data Sheet AS8446

Revision 1.8, Date 2005-03-17

Page 32 of 35

Analog buffer characterization

PARAMETER

SYMBOL

MIN

TYP

MAX

UNIT

NOTE

Input/Output voltage range

0.0

4.0

V

Offset voltage

80

mV

Slew rate

1.0

V/

µs

(1)

Failure Feedback Signal

There are two different ways to detect failures in the whole regulator system:

•

System failures detected directly on chip (e.g. over current, under voltage, …) and indicated by the appropriate failure

signal (e.g. Poverc, PVunder, …, respectively FAIL)

•

System failures detected by software of the controlling

µP via the monitoring of the motor current, motor speed, battery

voltage, temperature and duty cycle of the PWM signal (e.g. motor failures like blocked motor, open wires, …). This part of

system failures must be defined by the motor and system know how of the customer.

The following system failures are detected directly on the AS8446 chip:

1.

Over current of the motor (signal: Poverc)

2.

Under voltage of the battery voltage Vbat (signal: PVunder)

3.

Over voltage of the battery voltage Vbat (signal: PVover)

4.

Over temperature of external temperature (signal: PTover_ex)

5.

Over temperature of on chip temperature (signal: PTover_in)

6.

Under voltage of VDD (5 V) (signal: VDDunder)

7.

Over voltage of VDD (5 V) (signal: VDDover)

All these seven failures are stored in register R18 and can be read by the controlling

µP via the Three Wire Interface.

A failure signal FAIL is created by OR conjunction of these failures and put to the pin FAIL (can be used as an interrupt signal

for the

µP to start a read access via the Three Wire Interface to the failure register R18):

FAIL = Poverc or PVunder or PVover or PTover_ex or PTover_in or VDDunder or VDDover or TEMP_TEST

The first three failures (over current, over and under voltage) are used to switch off the driver output OUT immediately by on

chip hardware, the two temperature failure and the VDD over / under voltage failure are only detected and can be treated by

software of the

µP.

The signal TEMP_TEST is only used for test purposes and must be set low in the normal application. If there is a wrong value

(high) of TEMP_TEST during the normal application the FAIL signal is set and must be reset via the Three Wire Interface.

Wake-up System (Pin Wake-up)

PARAMETER

SYMBOL

MIN

TYP

MAX

UNIT

NOTE

DC Characteristics

Low Level Input Voltage

-8

V

High Level Input Voltage

V

Input Hysteresis

Pull- up Current on Input

-400

5

µA

> 30 k

Ω internal pull- up

Watch Dog and RESET

The watch dog can be used to supervise the function of the controlling

µP. In cases where this supervising is not necessary, the

watch dog is switched off via the Three Wire Interface by sending a zero to R16<0:0>.

The default value after the start up of the system is R16<0:0> = 0 (watch dog is not active).