3054 Datasheet, PDF (8/12 Pages) Allegro MicroSystems – MULTIPLEXED TWO-WIRE HALL-EFFECT SENSOR ICs

3054
MULTIPLEXED
TWO-WIRE
HALL-EFFECT SENSOR ICs
In Figure 4, the ADDRESS input provides a TTL-compatible input
to control the bus supply. A HIGH (5 V) input switches Q₁ ON and sets
the bus voltage to 6 V through the resistor divider R₄, R₅, and Zener
Z₁. A LOW input switches Q₁ OFF and sets the bus voltage to 9 V
(Z₁). This voltage is fed into the positive input of the operational
amplifier OP₁ and is buffered and made available at BUS SUPPLY (or
sensor supply). Bus reset control is also available in the form of a TTL-
compatible input. When the RESET input is HIGH, Q₂ is switched ON
and the positive input of the operational amplifier is set to the satura-
tion voltage of the transistor (approximately 0 V). This resets the bus.
A linear reading of the bus current is made possible by amplifying
the voltage generated across R₆ (which is I_BUS • R₆). The amplifier,
OP₂, is a standard differential amplifier of gain R₉/R₇ (provided that R₇
= R₈, R₉ = R₁₀). The gain of the total transim-pedance amplifier is
given by:
V_OUT = I_BUS • R₆ • R₉/R₇
This voltage is available at the ANALOG OUT terminal.
Bus Control Software
The processing of the bus current (available at ANALOG OUT) is
best done by feeding it into the A/D input of a microprocessor. If the
flexibility provided by a microprocessor is not desired, this signal could
be fed into threshold detection circuitry; e.g., comparator, and the
output used to drive a display.
Related References
1. G. AVERY, “Two-Terminal Hall Sensor,” ASSIGNEE: Sprague
Electric Company, North Adams, MA, United States. Patent number
4,374,333; Feb. 1983.
2. T. WROBLEWSKI and F. MEISTERFIELD, “Switch Status
Monitoring System, Single-Wire Bus, Smart Sensor Arrangement
There Of,” ASSIGNEE: Chrysler Motor Corporation, Highland Park, Ml,
United States. Patent number 4,677,308; June 1987.
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