33784 Datasheet, PDF (10/30 Pages) Freescale Semiconductor, Inc – DSI 2.02 Sensor Interface

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.
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.
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.
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.
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.
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
10
Analog Integrated Circuit Device Data
Freescale Semiconductor