3054 Datasheet, PDF (6/12 Pages) Allegro MicroSystems – MULTIPLEXED TWO-WIRE HALL-EFFECT SENSOR ICs

3054
MULTIPLEXED
TWO-WIRE
HALL-EFFECT SENSOR ICs
FIGURE 3
BUS INTERCONNECTION
ADDRESS
RESET
ANALOG OUT
(POSITIVE) BUS SUPPLY
01
02
28
BUS RETURN
29
30
Dwg. EH-005
31 is designed to be inactive to allow for
further address expansion of the bus (to 62
maximum 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 applying it to
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
Pin 3 of the IC 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’ or ‘closed’
(shorted to sensor ground).
APPLICATIONS NOTES
Magnetic Actuation
The left side of Figure 2 shows the wiring of an A3054KU or
A3054SU 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 an A3054KU or
A3054SU when used to detect the status of a mechanical switch.
In this case, pin 3 is connected to the switch. The other side of the
switch is connected to the bus return (negative bus supply or ground).
When the mechanical switch is closed, and the correct bus address is
detected by the IC, the sensor responds with a signal current. If the
switch is open, only the diagnostic current is returned.
Bus Configuration
A maximum of 30 individually addresable sensors may be con-
nected across the same two-wire bus as shown in Figure 3. It is
recommended that the sensors use a dedicated digital ground wire to
minimize the effects of changing ground potential (as in the case of
chassis ground in the automotive industry).
The bus was not designed to require two-wire twisted pair wiring to
the sensors. However, in areas of extreme electromagnetic interfer-
ence, it may be advisable to install a small bypass capacitor (0.01 µF
for example) between the supply and ground terminals of each sensor
instead of using the more expensive wiring.
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