3055 Datasheet, PDF (4/8 Pages) Allegro MicroSystems – MULTIPLEXED TWO-WIRE HALL-EFFECT SENSOR ICs

3055
MULTIPLEXED
TWO-WIRE HALL EFFECT
SENSOR IC
ADDRESSING PROTOCOL
The device may be addressed by modulating
the supply voltage as shown in Figure 1. A
preferred addressing protocol is as follows:
the bus supply voltage is brought down to 0V
so that all devices on the bus may be reset.
The voltage is then raised to the address
LOW voltage (V_L) and the bus quiescent
current is measured. The bus is then toggled
between V_L and V_H (address HIGH voltage),
with each positive transition representing an
increment in the bus address. After each
voltage transition, the bus current is moni-
tored to check for diagnostic and signal
responses from sensor ICs.
Sensor Addressing
When a sensor detects a bus address equal
to its factory programmed address, it re-
sponds with an increase in its supply current drain (called I_S during the
HIGH portion of the address cycle). This response may be used as an
indication that the sensor is alive and well on the bus and is also called
the diagnostic response. If the sensor detects an ambient magnetic
field, it also responds with I_S during the low portion of the address
cycle. This response from the sensor is called the signal response.
When the next positive transition is detected, the sensor becomes
disabled, and its contribution to the bus signal current returns to I_Q.
Bus Current
Figure 1 displays the above described addressing protocol. The top
trace represents the bus voltage transitions as controlled by the bus
driver (see applications note for an optimal bus driver schematic). The
second trace represents the bus current contribution of sensor (ad-
dress 02). The diagnostic response from the sensor indicates that it
detected its address on the bus; however, no signal response current
is returned, which indicates that sufficient magnetic field is not de-
tected at the chip surface. The third trace represents the current drain
of sensor 03 when a magnetic field is detected. Note both the diag-
nostic and signal response from the sensor. The last trace represents
FIGURE 1
BUS TIMING D1
BUS
VOLTAGE
V
H
VCLH
V
CHL
VL
V _RST
0
RESET
IS
SENSOR 02
CURRENT
WITH NO
MAGNETIC
FIELD
I _QL
I _QH
0
IS
SENSOR 03
CURRENT
WITH
MAGNETIC
FIELD
I _QL
I _QH
0
IS
TOTAL
BUS CURRENT
WITH
MAGNETIC
FIELD AT
SENSOR 03
n • I _QL
n • IQH
0
DIAGNOSTIC
ADDRESS 01
DIAGNOSTIC
ADDRESS 02
DIAGNOSTIC
ADDRESS 03
DIAGNOSTIC
ADDRESS 04
DIAGNOSTIC
ADDRESS n
t _plh
t _phl
SENSOR 02 —
DIAGNOSTIC CURRENT
SENSOR 03 — DIAGNOSTIC
AND SIGNAL CURRENTS
SENSOR 01
NOT PRESENT
RESET
DIAGNOSTIC
ADDRESS 01
SENSOR 01
NOT PRESENT
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