A1421, A1422, A1423
A1421-DS Rev. 0
Worcester, Massachusetts 01615-0036 (508) 853-5000
115 Northeast Cutoff, Box 15036
www.allegromicro.com
Allegro MicroSystems, Inc.
AB SO LUTE MAX I MUM RAT INGS
Supply Voltage, V
CC
..........................................28 V
Reverse-Supply Voltage, V
RCC
........................–18 V
Output Current, I
OUT
.......................................25 mA
Reverse-Output Current, I
ROUT
.....................–50 mA
Reverse-Output Voltage, V
ROUT
...................–50 mA
Operating Temperature
Ambient (L) , T
A
.........................–40ºC to 150ºC
Maximum Junction, T
J(max)
........................165ºC
Storage Temperature, T
S
..................–65ºC to 170ºC
High Accuracy Analog Speed Sensor
with Integrated Filter Capacitor
Package K, 4-pin SIP
Features and Benefi ts
• Integrated tracking capacitor
• Senses motion of ring magnet or ferrous targets
• Wide operating temperature range
• Operation with frequency of sensed transitions from 20 Hz to 30 kHz
• EMI/ESD-resistant
• Large effective air gaps
• 4.0 to 26.5 V operating range
• Output compatible with both TTL and CMOS logic families
• Reverse battery protection
• Resistant to mechanical and thermal stress
1. VCC
2. VOUT
3. Test pin, tie to GND
4. GND
1234
The A1421, A1422, and A1423 are ac-coupled Hall-effect sensors which include
monolithic integrated circuits that switch in response to changing differential
magnetic fi elds created by rotating ring magnets, or when coupled with a magnet,
by ferrous targets. This family of devices also includes an integrated capacitor,
providing the high accuracy of analog sensing without an external fi lter capaci-
tor. This reduces cost and components, while improving the reliability of the fi nal
sensor solution.
The magnetic fi eld changes are sensed by two integrated Hall transducers and then
are differentially amplifi ed on the chip. Differential sensing provides immunity to
radial vibration, within the device operating air gap range, by rejection of
common-mode signal changes. Steady-state system offsets are eliminated using an
on-chip differential bandpass fi lter with integrated capacitor. This fi lter also pro-
vides relative immunity to interference from electromagnetic sources. The device
utilizes advanced temperature compensation for the high-pass fi lter, sensitivity,
and Schmitt trigger switchpoints to guarantee optimal operation to low frequen-
cies over a wide range of air gaps and temperatures.
Each device includes a voltage regulator, two Hall transducers, temperature com-
pensating circuitry, a low-level amplifi er, bandpass fi lter, Schmitt trigger, and an
output driver. The on-board regulator permits operation with supply voltages from
4.0 to 26.5 V. The output stage can switch 20 mA over the full frequency response
range of the sensor, and is compatible with TTL and CMOS logic circuits.
Continued on next page.
Preliminary Data Sheet
Subject to Change Without Notice
June 16, 2004
Engineering samples available on a limited basis. Contact your local sales
or applications support offi ce for additional information.