33793 datasheet(10/27 Pages) FREESCALE

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Analog Integrated Circuit Device Data

Freescale Semiconductor

33793

FUNCTIONAL DESCRIPTION

INTRODUCTION

FUNCTIONAL DESCRIPTION

INTRODUCTION

The 33793 is designed to be used with a sensor at a

location that is remote from a centralized MCU. This device

provides power, measurement, and communications

between the remote sensor and the centralized MCU over a

DSI 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 DSI

bus in response to a query from the MCU. Four I/O lines can

be configured by the central MCU over the DSI bus as analog

inputs, digital inputs, or digital outputs. This allows more than

one sensor to be remotely controlled and measured by a

single 33793. Additionally, a high drive logic output is

provided that can be used to power other low-power sensors.

Power is passed from BUSIN or BUSOUT through on-

board rectifiers to a storage capacitor (referred to as the

H_CAP). The H_CAP stores energy during the highest

voltage excursions of the BUSIN or BUSOUT pin (idle) and

supplies energy to power the device during low excursions of

BUSIN and BUSOUT.

The Regulator supplies an on-board regulated voltage for

internal use, and the Power on Reset (POR) circuit provides

a reset signal during low-voltage conditions and during power

up/down. Some current is available for low-power sensors.

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

BUSIN and/or BUSOUT pins as voltage levels that are

sensed by the Level Detection circuitry. The Serial Decoder

detects these transitions and decodes the incoming data.

The Control Logic provides overall control of the 33793. It

controls diagnostic testing and formats responses to

commands with the message encoder. Responses are

formed via a switched current source that is slew-rate

controlled.

The one-time programmable (OTP) memory array

provides the nonvolatile storage for the pre-programmed

address. It is accessed via the Read/Write NVM command. It

has a built-in hardware lock that only allows one write.

FUNCTIONAL PIN DESCRIPTION

BUS RETURN (BUSRTN)

This pin provides the common return for power and

signalling.

INPUT/OUTPUT (I/O0, I/O1, I/O2, I/O3)

This pin can be used to provide a logic level output, a logic

input, or an analog-to-digital (A/D) input.

ANALOG GROUND (AGND)

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

analog-to-digital converter (ADC).

LOGIC OUT (LOGOUT)

This is a logic output with higher pull-up drive capability

than the standard logic I/O.

REGULATOR OUTPUT (REGOUT)

This pin provides a regulated 5.0 V output. The power is

derived from the bus.

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.

DSI BUS INPUT (BUSIN)

This pin attaches to the bus and responds to initialization

commands.

DSI BUS OUTPUT (BUSOUT)

This pin attaches to the bus and responds to reverse

initialization commands.

FUNCTIONAL INTERNAL BLOCK DESCRIPTION

Refer to Figure 2, 33793 Internal Block Diagram, page 3,

for a simplified representation of the 33793’s components.

RECTIFIER

This rectifier or switch peak detects the bus signal into an

external capacitor attached to H_CAP. The capacitor

supplies power during signaling while the input voltage is at a

lower level.

The voltage waveform at BUSIN and/or BUSOUT and the

size of the filter capacitor at H_CAP must be such that the

voltage at H_CAP will not drop below the frame threshold

during signaling.

POR

The 33793 leaves the reset state when the voltage on

H_CAP rises above the Power-ON Reset threshold.

TIMEOUT

A timeout timer keeps track of the length of the time when

the input is not in idle mode. If this time exceeds a limit, the

33793 Datasheet(PDF) 10 Page - Freescale Semiconductor, Inc

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