3197
PROTECTED, HIGH-TEMPERATURE,
OPEN-COLLECTOR HALL-EFFECT LATCH
These open-collector Hall-effect latches are capable of sensing magnetic
fields while using an unprotected power supply. The A3197LLT and A3197LU
can provide position and speed information by providing a digital output for
magnetic fields that exceed their predefined switch points. These devices
operate down to zero speed and have switch points that are designed to be
extremely stable over a wide operating temperature and voltage range. The
latching characteristics make them ideal for use in pulse counting applications
when used with a multi-pole ring magnet. Thermal and output short-circuit
protection allow an increased wiring harness fault tolerance. The temperature
compensated switch points, the wide operating voltage range, and the integrated
protection make these devices ideal for use in automotive applications such as
transmission speed sensors and integrated wheel bearing speed sensors.
3
Data Sheet
27609.10A
X
PTCT
V
CC
1
2
Dwg. PH-003-2
Each monolithic device contains an integrated Hall-effect transducer, a
temperature-compensated comparator, a voltage regulator, and a buffered 35 mA
output sink stage. Supply protection is made possible by the integration of
overvoltage and undervoltage shutdown circuitry that monitor supply fault
conditions and shut down the IC. Noise shutdown circuitry (patent applied for)
prevents the propagation of supply transients to the logic load. Output protec-
tion circuitry includes a current limit loop that limits the maximum output sink
current, and thermal protection circuitry that shuts down the device during an
over-heating condition such as with a shorted load.
The A3197LLT and A3197LU are rated for operation over an extended
temperature range of -40°C to +150°C. They are supplied in a three-lead SIP
(suffix ‘U’) or a surface-mount SOT-89 (suffix ‘LT’).
GROUND
ABSOLUTE MAXIMUM RATINGS
Supply Voltage, V
CC
(100 ms) ...................................
115 V*
(continuous) ...............................
28 V*
Reverse Battery Voltage, V
RCC
(100 ms) ...................................
-100 V
(continuous) ...............................
-35 V
Magnetic Flux Density, B ..........
Unlimited
Output OFF Voltage, V
OUT
.................
26 V
Reverse Output Voltage V
OUT
.........
-0.5 V
Continuous Output Current,
I
OUT
..........................................
35 mA*
Reverse Output Current,
I
OUT
........................................
-100 mA
Package Power Dissipation,
P
D
.......................................
See Graph
Junction Temperature, T
J
.................
170
°
C
Operating Temperature Range,
T
A ..........................................
-40
°
C to +150
°
C
Storage Temperature, T
S
..................
170
°
C
*Fault condition, internal overvoltage shutdown
above 28 V; output current limited above 35 mA.
OUTPUT
SUPPLY
FEATURES
I
I
I
I
I
I
I
I
I
I
Internal Protection For Automotive (ISO/DIN) Transients
Operation From Unregulated Supply
Reverse Battery Protection
Undervoltage Lockout
Supply Noise-Suppression Circuitry
Output Short-Circuit Protection
Output Zener Clamp
Thermal Protection
Symmetrical Latching Switch Points
Operable with Multipole Ring Magnets
Always order by complete part number, e.g.,
A3197LU
.
3197
PROTECTED, HIGH-TEMP.,
OPEN-COLLECTOR
HALL-EFFECT LATCH
FUNCTIONAL BLOCK DIAGRAM
1
V
CC
OVERVOLT.
LOCKOUT
REG.
POWER UP &
TRANSIENT
PROTECTION
3
OUTPUT
CONTROL
X
THERMAL
SHUTDOWN
CURRENT
LIMIT
<1Ω
2
Dwg. FH-012A
GROUND
800
ALLOWABLE PACKAGE POWER DISSIPATION IN mW
700
600
500
400
300
200
100
0
"LT" PACKAGE
R
θJA
= 258°C/W
"U" PACKAGE
R
θJA
= 183°C/W
NOTE – Permitted duty cycle will be less than 100%
at maximum ambient temperature with high supply
voltages, i.e., T
A
≥
140°C, V
CC
≥
12 V, and the “LT”
package. The thermal shutdown circuitry does not
protect the device from these stresses (see Internal
Protective Features).
20
40
60
100
140
80
120
AMBIENT TEMPERATURE IN
°C
160
180
Dwg. GH-054A
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
Copyright © 1995, 1999, Allegro MicroSystems, Inc.
3197
PROTECTED, HIGH-TEMP.,
OPEN-COLLECTOR
HALL-EFFECT LATCH
OPERATION
In operation, the output transistor is OFF
until the strength of the magnetic field
perpendicular to the surface of the chip
exceeds the threshold or operate point (B
OP
).
When the field strength exceeds B
OP
, the
output transistor switches ON
(a logic low) and is capable of sinking
35 mA of current.
The output transistor switches OFF (a
logic high) when magnetic field reversal
results in a magnetic flux density below the
OFF threshold (B
RP
). This is illustrated in
the transfer characteristics graph. Note that
the device latches; that is, a south pole of
sufficient strength will turn the device ON.
Removal of the south pole will leave the
device ON. The presence of a north pole of
sufficient strength is required to turn the
device OFF.
The switch points increase in sensitivity
with increasing temperature to compensate
for the typical ferrite magnet temperature
characteristic. The simplest form of magnet
that will operate these devices is a ring
magnet. Other methods of operation are
possible.
TEST CIRCUIT AND TYPICAL APPLICATION
V
CC(UV)
TO 26 V
WITH TRANSIENTS
V
CC
1
REGULATED
< 26 V
V
BB
R
L
3
TO
µP
C
BYPASS
X
C
L
2
Dwg. EH-006A
26 V
MAX
V
BB
OUTPUT VOLTAGE IN VOLTS
B
RP
B
OP
V
OUT(SAT)
0
-B
0
FLUX DENSITY
+B
Dwg. GH-034-2A
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