3055
MULTIPLEXED
TWO-WIRE HALL EFFECT
SENSOR IC

The UGN3055U Hall-effect sensor is a digital magnetic sensing IC

capable of communicating over a two-wire power/signal bus. Using a
sequential addressing scheme, the device responds to a signal on the
bus and returns the diagnostic status of the IC, as well as the status of
each monitored external magnetic field. As many as 30 sensors can
function on the same two-wire bus. This IC is ideal for multiple sensor
applications where minimizing the wiring harness size is desirable or
essential.

The device consists of high-resolution bipolar Hall-effect switching

circuitry, the output of which drives high-density CMOS logic stages.
These logic stages decode the address pulse and enable a response
at the appropriate address. The combination of magnetic-field or
switch-status sensing, low-noise amplification of the Hall-transducer
output, and high-density decoding and control logic is made possible
by the development of a new sensor BiMOS fabrication technology.

This unique magnetic sensing IC operates within specifications

between -20

C and +85

C. Alternate magnetic and temperature

specifications are available upon request. It is supplied in a 60 mil
(1.54 mm) thick, three-pin plastic SIP. Each package is clearly marked
with a two-digit decimal device address (xx).

Pinning is shown viewed from branded side.

Dwg. PH-005

BUS

GROUND

SWITCH IN

LOGIC

MULTIPLEXED TWO-WIRE

HALL-EFFECT SENSOR ICs

FEATURES

Complete Multiplexed Hall-Effect IC with

Simple Sequential Addressing Protocol

Allows Power and Communication Over a

Two-Wire Bus (Supply/Signal and Ground)

Up to 30 Hall-Effect Sensors Can Share a Bus

Sensor Diagnostic Capabilities

Magnetic-Field or Switch-Status Sensing

Low Power of BiMOS Technology Favors

Battery-Powered and Mobile Applications

Ideal for Automotive, Consumer, and Industrial Applications

Always order by complete part number:

UGN3055U

ABSOLUTE MAXIMUM RATINGS

at T

= +25

Supply Voltage, V

BUS

........................... 24 V

Magnetic Flux Density, B ............ Unlimited
Operating Temperature Range,

..........................

-20

C to +85

Storage Temperature Range,

.............................. -55

C to +150

Package Power Dissipation,

....................................

750 mW

Data Sheet

27680

3055

DISCONTINUED PRODUCT

Shown for Reference Only

115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000

3055
MULTIPLEXED
TWO-WIRE HALL EFFECT
SENSOR IC

Electrical

Limits

Symbol

Min.

Typ.

Max.

Units

Power Supply Voltage

BUS

Signal Current

Quiescent Current

BUS

= 6 V

2.5

BUS

= 9 V

2.5

300

Address Range

Addr

Clock Thresholds

LOW to HIGH

CLH

8.5

HIGH to LOW

CHL

6.5

Hysteresis

CHYS

0.8

Clock Period

CLK

0.1

1.0

Address LOW Voltage

RST

CHL

Address HIGH Voltage

CLH

BUS

Power-On Reset Voltage

RST

2.5

3.5

5.5

Settling Time

BUS

= 9 V

100

BUS

= 6 V

100

Propagation Delay

LOW to HIGH

plh

HIGH to LOW

phl

Pin 3 Input Resistance

No Magnetic Field (V

OUT

= HIGH)

OUTH

Mag. Field Present (V

OUT

= LOW)

OUTL

Magnetic Characteristics

Magnetic Thresholds

*Turn-On

150

300

Turn-Off

-25

100

300

Hysteresis (B

)

HYS

Characteristics

OPERATIONAL CHARACTERISTIC over operating temperature range.

*Alternate magnetic switch point specifications are available on request. Please contact the factory.

W
Copyright © 1988, 1991, Allegro MicroSystems, Inc.

3055
MULTIPLEXED
TWO-WIRE HALL EFFECT
SENSOR IC

FUNCTIONAL BLOCK DIAGRAM

SENSOR LOCATION

(

0.005" [0.13 mm] die placement)

Dwg. MH-002A

0.015"
0.38 mm

NOM

0.071"

1.80 mm

0.084"

2.13 mm

BRANDED
SURFACE

ACTIVE AREA DEPTH

CLOCK

Dwg. FH-009

BUS

SWITCH IN

(OPTIONAL)

GROUND

CMOS LOGIC

REG

COMP

RESET

DEFINITION OF TERMS

Sensor Address

Each bus sensor has a factory-specified predefined
address. At present, allowable sensor addresses are
integers from 1 to 30.

LOW-to-HlGH Clock Threshold (V

CLH

)

Minimum voltage required during the positive-going
transition to increment the bus address and trigger a
diagnostic response from the bus sensors. This is also
the maximum threshold of the on-chip comparator, which
monitors the supply voltage, V

BUS

HlGH-to-LOW Threshold (V

)

Maximum voltage required during the negative-going
transition to trigger a

signal current response from the bus

sensors. This is also the maximum threshold of the on-
chip comparator, which monitors the supply voltage, V

BUS.

Bus HIGH Voltage (V

)

Bus HIGH voltage required for addressing. Voltage
should be greater than V

CLH

Address LOW Voltage (V

)

Bus LOW Voltage required for addressing. Voltage
should be greater than V

RST

and less than V

CHL

Bus Reset Voltage (V

RST

)

Voltage level required to reset individual sensors.

Sensor Quiescent Current Drain (I

)

The current drain of bus sensors when active but not
addressed. I

is the maximum quiescent current drain

when the sensor is not addressed and is at V

. I

is the

maximum quiescent current drain when the sensor is not
addressed and is at V

Diagnostic Phase

Period on the bus when the address voltage is at V

During this period, a correctly addressed sensor responds
by increasing its current drain on the bus. This response
from the sensor is called the diagnostic response and
the bus current

increase is called the diagnostic current.

Signal Phase

Period on the bus when the address voltage is at V

. During

this period, a correctly addressed sensor that detects a
magnetic field greater than magnetic Operate Point, B

responds by maintaining a current drain of I

on the bus.

This response from the sensor is called the signal response
and the bus current

increase is called the signal current.

Sensor Address Response Current (I

)

Current returned by the bus sensors during the

diagnostic and

the

signal responses of the bus sensors. This is accomplished

by enabling the constant current source (CCS).

Magnetic Operate Point (B

)

Minimum magnetic field required to switch ON the Hall
amplifier and switching circuitry of the addressed sensor.
This circuitry is only active when the sensor is addressed.

Magnetic Release Point (B

)

Magnetic field required to switch OFF the Hall amplifier
and switching circuitry after the output has switched ON.
This is due to magnetic memory in the switching circuitry.
However, when a device is deactivated by changing the
current bus address, all magnetic memory is lost.

Magnetic Hysteresis (B

HYS

)

Difference between the B

and B

magnetic field thresh-

olds.

115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000

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 0 V
so that all devices on the bus may be reset.
The voltage is then raised to the address
LOW voltage (V

) and the bus quiescent

current is measured. The bus is then toggled
between V

and V

(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

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

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

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

SENSOR 03 -- DIAGNOSTIC

AND SIGNAL CURRENTS

DIAGNOSTIC
ADDRESS 01

DIAGNOSTIC
ADDRESS 02

DIAGNOSTIC
ADDRESS 04

DIAGNOSTIC

ADDRESS

RESET

DIAGNOSTIC

ADDRESS 01

SENSOR 02 --
DIAGNOSTIC CURRENT

DIAGNOSTIC
ADDRESS 03

SENSOR 01

NOT PRESENT

RST

I QH

n · I QL

n · IQH

t phl

t plh

CLH

CHL

Dwg. WH-005

BUS

VOLTAGE

SENSOR 02

CURRENT

WITH NO

MAGNETIC

FIELD

SENSOR 03

CURRENT

WITH

MAGNETIC

FIELD

TOTAL

BUS CURRENT

WITH

MAGNETIC

FIELD AT

SENSOR 03

RESET

I QH

SENSOR 01

NOT PRESENT

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

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

), 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

. 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

Dwg. EH-004

SWITCH

POSITIVE BUS SUPPLY

BUS RETURN

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