33784 datasheet(10/30 Pages) FREESCALE

10 / 30 page

Analog Integrated Circuit Device Data

Freescale Semiconductor

33784

FUNCTIONAL DESCRIPTION

INTRODUCTION

FUNCTIONAL DESCRIPTION

INTRODUCTION

The 33784 is designed to be used with a sensor at a

location remote from a centralized MCU. This device

provides power, measurement, and communications

between the remote sensor and the centralized MCU over a

DSI 2.02 compliant bus. Sensors such as accelerometers

can be powered from the regulated output of the device, and

the resulting analog value from the sensor can be converted

from an analog level to a digital value for transmission over

the bus, in response to a query from the MCU. There are two

analog inputs to a 10-bit analog-to-digital converter (ADC).

Three I/O lines can be configured by the central MCU over

the bus as digital inputs or digital outputs.

Power is passed from BUSIN through on-chip rectifiers to

an external storage capacitor. The capacitor stores energy

during the highest voltage excursions of the BUSIN pin (idle)

and supplies energy to power the device during low

excursions of BUSIN.

An under-voltage circuit provides a reset signal during low-

voltage conditions and during power-up/power-down.

Data from the Central Control Unit (CCU) is applied to the

BUSIN pin as voltage levels that are sensed by level

detection circuitry. A serial decoder detects these transitions

and decodes the incoming data. Responses are passed

through a serial encoder and are transmitted via a switched

current source that is slew-rate controlled.

FUNCTIONAL PIN DESCRIPTION

ANALOG GROUND (AGND)

This pin is the low reference level and power return for the

analog-to-digital converter (ADC). It is internally connected to

RTNIN

TEST OUTPUT (TOUT)

This output is low for normal operation and will go high

when the device is placed into a test mode. See Test Mode

on page 14.

IDDQ (IDDQ)

This input is used for measuring the quiescent current of

the device during IC manufacturing test. This pin should be

open in the application.

ANALOG INPUT (AN0, AN1)

Inputs to the analog-to-digital converter.

LOGIC I/O (I/O0, I/O1, I/O2)

These pins provide a logic level outputs or inputs.

TEST MODE ENABLE (TEST)

A high input places this device into special test mode. See

Test Mode on page 14.

HOLDING CAPACITOR (H_CAP)

A capacitor attached to this pin is charged by the bus

during bus idle and supplies current to run the device and for

external devices via the REGOUT pin during non-idle

periods.

DBUS INPUT (BUSIN)

This pin attaches to the high side of the differential bus and

responds to initialization commands.

BUS RETURN IN (RTNIN)

This pin connects to the low side of the differential bus and

provides the common return for power and signalling. It is

internally connected to AGND.

DBUS OUTPUT (BUSOUT)

This pin is the switched BUSIN signal and is connected to

the BUSIN pin of the next device in the daisy chain.

BUS RETURN OUT (RTNOUT)

This pin is the switched RTNIN signal and is connected to

the RTNIN pin of the next device in the daisy chain.

33784 Datasheet(PDF) 10 Page - Freescale Semiconductor, Inc

33784 Datasheet(HTML) 10 Page - Freescale Semiconductor, Inc

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