AS8846 datasheet(2/35 Pages) AMSCO

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Data Sheet AS8446

Revision 1.8, Date 2005-03-17

Page 2 of 35

Functional Description

Overview

The AS8446 is a complex integrated circuit, which contains

both low and high voltage circuitry to regulate PWM brush DC

motors with an external n-channel power FET and an

8-bit

µP. The regulation loop is a closed loop environment

where a

µP is connected to the device with a Three-Wire

Interface. The AS8446 measures and delivers the motor

current as an analog value to the

µP. The µP uses a special

algorithm to calculate the motor speed by considering the

motor current as a function of time. This technique allows the

system to act either as a motor current or a motor speed

regulator. The AS8446 also monitors and delivers the battery

voltage to the

µP as an analog value and by leveraging this

voltage-monitoring feature a motor voltage regulator could

be implemented also. A full diagnosis of motor and power FET

failures is performed automatically by the programmable

failure handling functions after carefully analyzing the motor

characteristics, real-time motor current, motor speed and

battery voltage.

The dynamically self-adjusting slew rate regulated switching

technology (patented) is one of the most important features of

this ASSP in automotive applications. This technology

enables two features of the PWM DC motor regulator, which

were up till now impossible to realize:

•

Excellent EMC behavior (very low RF emission in the

whole frequency range)

•

High power efficiency up to 96 % @ fPWM = 20 kHz

(fall / rise time down up to < 150 ns)

Most of the parameters (e.g. PWM frequency, slew rate, over

current threshold, current measurement range, etc.) of the

AS8446 can be programmed (setting up the internal registers)

through the Three-Wire Interface, which makes the regulator

a versatile and easily adaptable device to a wide range of

regulation modes and motors.

The field programmability option of the slew rate regulation

parameters makes it easier to comply with the system level

EMC behavior (regulator board, motor, power cables, etc.)

A bandgap is used as a reference for a Low Drop Voltage

Regulator with a nominal output voltage of 5 V.

This regulator is capable to deliver a supply current of up to

40 mA. Higher current is possible with an external bipolar

transistor.

The device is bundled with a set of software to handle the

regulation loop, motor speed measurement and failure

detection. A sleep/wake up system is integrated to bring the

AS8446 into a power save mode. It is controlled via the

specified wake-up pin.

A short overview of the main features follows.

•

programmable PWM DC motor current, speed or voltage

regulator

•

single voltage supply in the range Vbat = 6.0V to 18V

(Vbat,max = 30 V)

•

Low-Battery-Mode guarantees operation also when

battery voltage is between 6.0V and 6.5V; In this mode

the output driver is constantly on (100% PWM),

Vpump-Vbat

≥ 4.0V.

•

applicable directly to the automotive battery supply

(burst, surge, load dump)

•

closed loop regulation of the motor speed, motor current

or motor voltage with a

µP.

•

high power efficiency of the whole regulator module (up

to 96 % @ fPWM = 20 kHz)

•

low RF emission within the whole frequency range

•

fully protected by programmable failure handling

procedures (see below: Security Functions)

•

fast over current and over / under voltage detection and

protection

•

motor current and motor speed measurement with only

one shunt resistor (typ. measurement voltage at nominal

motor current: 50 mV)

•

on chip trimming capability of the external shunt resistor

•

Sleep/wake up mode system controlled by the

µP and

the wake-up pin

•

Three Wire Interface

•

programming possibilities of the following regulator

parameters inside of the AS8446:

PWM frequency (generated by

µP, e.g. 20 kHz)

charge pump voltage monitoring and protection

slew rate control parameters (EMC behavior)

power FET Gate driver currents up to 500 mA

over current threshold level

over / under voltage threshold level

motor current measurement range and trimming of

the external current measurement resistor

•

programming possibilities of the following regulator

parameters / functions via the

µP

motor failure threshold levels (motor currents and

voltages) for all motor failures: blocked motor, open

wire, no load, shorted motor segments, etc.

failure handling procedures for all motor failures,

over / under voltage and for over temperature (type

of reaction and timing)

sleep mode criteria and sleep mode signal to the

AS8446

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