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33793 Datasheet PDF : 24 Pages
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Freescale Semiconductor, Inc.
SYSTEM/APPLICATION INFORMATION
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 DESCRIPTION
Refer to Figure 1, 33793 Internal Block Diagram, page 2, 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.
Undervoltage Detector
The undervoltage detector monitors the output voltage of the
5.0 V regulator. If the REGOUT voltage drops too low for
accurate A/D operation, a signal is sent to the control logic. The
control logic will interpret this signal and, in response to a
command, report a status indicating an undervoltage condition
to have existed. When received, the command will clear the
signal after having read the status. If the voltage is too low when
the A/D conversion was completed, the returned value will be
zero (binary 00000000).
IO Pins 0 to 3
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 part is
reset. The purpose of this is to allow the part to reset itself if the
connection to the master is lost or if power is removed from the
system.
5.0 V Regulator
The IO pins can serve as logic inputs, logic outputs, or
analog inputs. At power-up or after a clear, the pins are all logic
inputs and can be used to measure an analog level value for an
analog value request command. The pins can be individually
configured as logic inputs or outputs by the IO Control
command. If the pin is configured as a logic output, reading the
analog value will return the analog level the output is being
driven to.
Analog-to-Digital Converter
The ADC is an 8-bit successive approximation type using on-
board capacitive division. It uses the Clk signal from the on-
board oscillator for sequencing.
The 5.0 V regulator supplies internal power for the device
and also provides approximately 6.0 mA through the REGOUT
pin to power an external sensor.
The ADC uses REGOUT as a full-scale reference voltage
and ground AGND for a zero-level reference.
The ADC signals when it has made a valid conversion by
asserting a signal to the controller. If this signal is not asserted
MOTOROLA ANALOG INTEGRATED CIRFCoUrITMDEoVrIeCEIDnAfoTArmation On This Product,
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