3055 Datasheet, PDF (5/8 Pages) Allegro MicroSystems – MULTIPLEXED TWO-WIRE HALL-EFFECT SENSOR ICs

3055
MULTIPLEXED
TWO-WIRE HALL EFFECT
SENSOR IC
the overall bus current drain. When no
sensors are addressed, the net bus current
drain is the sum of quiescent currents of all
sensors on the bus (for ‘n’ sensors, the bus
quiescent current drain is n * I_Q).
Bus Issues
At present, a maximum of 30 active sensors
can coexist on the same bus, each with a
different address. Address 0 is reserved for
bus current calibration in software. This
feature allows for fail-safe detection of signal
current and eliminates detection problems
caused by low signal current (I_S), the opera-
tion of sensors at various ambient tempera-
tures, lot-to-lot variation of quiescent current,
and the addition and replacement of sensors
to the bus while in the field. Address 31 is
designed to be inactive to allow for further
address expansion of the bus (to 62 maxi-
mum addresses). In order to repeat the
address cycle, the bus must be reset as
shown in Figure 1 by bringing the supply
voltage to below V_RST. Sensors have been
designed not to ‘wrap-around’.
Magnetic Sensing
The sensor IC has been designed to respond
to an external magnetic field whose magnetic
strength is greater than B_OP. It accomplishes
this by amplifying the output of an on-chip
Hall transducer and feeding it into a threshold
detector. In order that bus current is kept to
a minimum, the transducer and amplification
circuitry is kept powered down until the
sensor is addressed. Hence, the magnetic
status is evaluated only when the sensor is
addressed.
External Switch Sensing
The third pin of the IC (pin 3) may be used to
detect the status of an external switch when
magnetic field sensing is not desired (and in
the absence of a magnetic field). The
allowable states for the switch are ‘open’ and
‘closed’ (shorted to sensor ground).
APPLICATIONS NOTES
Magnetic Actuation
The left side of Figure 2 shows the wiring of the UGN3055U when
used as a magnetic threshold detector. Pin 1 of the sensor is wired to
the positive terminal of the bus, pin 2 is connected to the bus negative
terminal, and pin 3 has no connection.
Mechanical Actuation
The right side of Figure 2 shows the wiring of the UGN3055U when
used to detect the status of a mechanical switch. In this case, pin 3 is
connected to the positive terminal of the switch. The negative side of
the switch is connected to the negative terminal of the bus. When the
mechanical switch is closed (shorted to ground) and the correct bus
address is detected by the IC, the sensor responds with a signal
current. If the switch is open, only a diagnostic current is returned.
FIGURE 2
SENSOR CONNECTIONS
POSITIVE BUS SUPPLY
X
X
12 3
NC
12 3
BUS RETURN
SWITCH
Dwg. EH-004