A1425LK-T Allegro Microsystems Inc, A1425LK-T Datasheet - Page 10

• Manufacturer Part Number: A1425LK-T
• Description: IC,HALL-EFFECT SWITCH,DIFFERENTIAL,SIP,4PIN,PLASTIC
• Manufacturer: Allegro Microsystems Inc
• Type: Special Purposer

Specifications of A1425LK-T

• Rohs Compliant: YES
• Sensing Range: 11G Trip, -11G Release
• Voltage - Supply: 4 V ~ 26.5 V
• Current - Supply: 7mA
• Current - Output (max): 25mA
• Output Type: Digital, Open Collector
• Features: High Accuracy
• Operating Temperature: -40°C ~ 150°C
• Package / Case: 4-SIP
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

A1425
The A1425 is a versatile high-precision differential Hall-effect
device that can be used in a wide range of applications. Proper
choice of the target material and shape, and assembly techniques
enables large working air gaps and high switchpoint accuracy
over the device operating temperature range.
Device Operation
The A1425 sensor IC contains two integrated Hall transducers
that are used to differentially respond to a magnetic fi eld across
the surface of the IC. Referring to fi gure 1, the trigger switches
the output off (output high) when the differential magnetic fi eld
crosses zero while increasing in strength (referred to as the posi-
tive direction), and switches the output on (output low) when
the differential magnetic fi eld crosses zero while decreasing (the
negative direction).
The operation is achieved through the use of two separate com-
parators. Both comparators use the same reference point, 0 G, to
provide high accuracy, but one comparator has a positive hyster-
esis, B
one comparator switches (B
ing differential signal and the other switches (B
crossing on a decreasing differential signal. The hysteresis on
each comparator precludes false switching on noise or target jitter.
HYS1
Figure 1. Typical output characteristics with dual comparator operation. Characteristics shown without delay, see Characteristic
Data section charts for delay and phase shift contributions.
, and the other a negative hysteresis, B
Output Signal, V
Applied Magnetic
Switching State
Comparator 1
Comparator 2
Field, B
OUT
diff
OP
–11.0
) at the zero crossing on an increas-
11.0
0.0
High Accuracy Analog Speed Sensor IC with Integrated
Filter Capacitor and Dual Zero-Crossing Output Signal
Off
RP
HYS2
) at the zero
Functional Description
. Therefore,

B
B
HYS2
Start-up
During power-on time, t
Beyond this time, if the applied magnetic fi eld, B
less than 50 G peak-to-peak, the switching state and V
ity are indeterminate. V
the additional settling time, t
t
chip capacitor. This feature reduces t
time constant of a high-pass fi lter.
Delay
The on-chip band-pass fi lter induces delay in the output signal,
V
shown in the Characteristic Data section quantify the effect of the
input signal amplitude on the phase shift of the output.
AC-Coupled Operation
Steady-state magnet and system offsets are eliminated using an
on-chip differential band-pass fi lter. The low and high frequency
poles of this band-pass fi lter are set using internal integrated
capacitors and resistors. The differential structure of this fi lter
improves the ability of the IC to reject single-ended noise on
the ground (GND pin) or supply line (VCC pin) and, as a result,
makes it more resistant to electromagnetic interference typically
seen in hostile remote-sensing environments.
RP(typ)
PO
On
OUT
B
, a circuit in the A1425 is briefl y enabled that charges the on-
OP(typ)
, relative to the applied magnetic fi eld, B
B
HYS1

OUT
PO
, the output signal, V
115 Northeast Cutoff
1.508.853.5000; www.allegromicro.com
Off
Allegro MicroSystems, Inc.
Worcester, Massachusetts 01615-0036 U.S.A.
will be valid for B
Settle
, has also elapsed. Also during
t+
PO
B
B
, relative to the long RC
OP(max)
OP(min)
/ B
/ B
diff
diff
OUT
RP(min)
RP(max)
. Simulation data
diff
> 50 Gp-p, after
, is high.
, is absent or
OUT
polar-
10