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Part: A3425EK
Category:
Sensors
-> Hall Effect Sensors
Description: Ultra-sensitive Dual-channel Quadrature Hall-effect Bipolar Switch
Company: Allegro Micro Systems, Inc.
Datasheet: Download A3425EK datasheet File size : 116 kB
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A3425
PIN OUT DIAGRAM
Ultra-Sensitive Dual-Channel Quadrature Hall-Effect Bipolar Switch
The A3425 is a dual-channel, Bipolar switch with two Hall-effect sensors, each providing a separate digital output for speed and direction signal processing capability. The Hall elements are both photo-lithographically aligned to better than 1µm. Maintaining accurate mechanical location between the two active Hall elements eliminates the major manufacturing hurdle encountered in fine-pitch detection applications. The A3425 is a highly sensitive, temperature stable magnetic sensor ideal for use in ring magnet based speed and direction systems located in harsh automotive and industrial environments. The A3425 monolithic integrated circuit contains two independent Hall effect switches located 1 mm apart. The digital outputs are out of phase so that the outputs are in quadrature with the proper ring magnet design. This allows for easy processing of speed and direction signals. Extremely low-drift amplifiers guarantee symmetry between the switches to maintain signal quadrature. The patented chopper-stabilization technique cancels offsets in each channel providing stable operation over temperature and voltage. An on-chip low dropout regulator allows the use of this device over a wide operating voltage range. Post-assembly factory programming at Allegro provides for sensitive switch points that are symmetrical between the two switches. The A3425 is available in a plastic 8-pin SOIC surface mount package and a 4-pin SIP. Always order using the complete part number: A3425EL, A3425LL, A3425EK, A3425LK
SOIC
K
Pin 1 : Pin 2 : Pin 3 : Pin 4 :
Supply Output A Output B Ground
Pin 5 : Pin 6 : Pin 7 : Pin 8 :
No connection No connection No connection No connection
ABSOLUTE MAXIMUM RATINGS
Supply Voltage VCC ....26.5V Reverse-Battery Voltage VRB ............ -18 V Output OFF Voltage VOUT ............ VCC Output Sink Current IOUT(SINK) .... Internally limited Magnetic Flux Density B ......... Unlimited Maximum Junction Temperature TJ (max) .. 165°C Package Power Dissipation JA (K).... 177 °C / W 108 °C / W JA (SOIC)..... Operating Temperature Range, TA Suffix "E" .......... - 40 °C to + 85 °C Suffix "L" .......... - 40 °C to + 150 °C Storage Temperature Range TS .... - 65 °C to + 170 °C
FEATURES & BENEFITS
Two matched Hall switches on a single substrate 1 mm sensor spacing Superior temperature stability Integrated LDR provides 3.3 V operation Integrated ESD Protection from outputs and VCC to ground High sensitivity switch points Robust structure for EMC protection Solid-state reliability
A3425-DS Rev. 1
A3425 ULTRA-SENSITIVE DUAL-CHANNEL QUADRATURE BIPOLAR SWITCH OPERATING CHARACTERISTICS
Valid over operating temperature range unless otherwise noted, typical data applies to VCC = 12 V and TA = 25°C
Characteristics
Symbol
Test Conditions
Min. 3.3
Limits Typ. Max. <1 110 55 18 10
Units V µA ns ns
ELECTRICAL CHARACTERISTICS Supply Voltage1 Output Leakage Current Output Rise Time Output Fall Time Supply Current Low Output Voltage Output Sink Current Output Sink Current, Continuous2 Output Sink Current, Peak3 Chopping Frequency Supply Zener Clamp Voltage Supply Zener Current
5
VCC IOFF tr tf ICC(OFF) ICC(ON) VSat Iou Iout_maxc Iout_maxp fC VZ IZ IRCC
BOP(A), BOP(B) BRP(A), BRP(B)
Operating; TA BOP(A) ,B > BOP(B) Both Outputs; ISINK = 20 mA; B > BOP(A), B > BOP(B) TJ < TJ(max) ,VOUT = 12 V t < 3 seconds
-
3.5 4.0 160 340
6.0 6.0 500 20 70 220 -
mA mA mV mA mA mA kHz V
TRANSIENT PROTECTION CHARACTERISTICS ICC = 9 mA4,TA = 25°C VS = 28 V VRCC = -18 V, TJ < TJ(max) TA = -40 °C TA = -40 °C TA = -40 °C TA = -40 °C TA = -40 °C TA = -40 °C +150 °C +150 °C +150 °C +150 °C +150 °C +150 °C -30 5 -35 -25 -25 2 7.0 -7.0 14 28 9.0 15 30 35 35 25 25 mA mA G G G G G G
Reverse Battery Current MAGNETIC CHARACTERISTICS Operate Point : B > BOP Release Point : B < BRP Hysteresis : BOP(A) - BRP(A), BOP(B) - BRP(B) Symmetry : Ch A, Ch B BOP(A) + BRP(A), BOP(B) + BRP(B) Operate Symmetry : BOP(A) BOP(B) Release Symmetry : BRP(A) BRP(B)
BHYS(A), BHYS(B) SYMA, SYMB ABSYMOP ABSYMRP
1 2 4 5
Maximum voltage operation must not exceed maximum junction temperature. Refer to power de-rating curves. Device will survive the current level specified but operation within magnetic specification cannot be guaranteed. 3 Short circuit of the output to Vcc is protected for the time duration specified.
Test current is equivalent to Icc max + 3 mA Maximum specification limit is equivalent to Icc max + 3 mA A3425-DS Rev. 1 Page 2
115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 Copyright © 2001, 2003 Allegro MicroSystems, Inc.
A3425 ULTRA-SENSITIVE DUAL-CHANNEL QUADRATURE BIPOLAR SWITCH FUNCTIONAL DESCRIPTION
Chopper-Stabilized Technique A limiting factor for switch point accuracy when using Hall effect technology is the small signal voltage developed across the Hall plate. This voltage is proportionally small relative to the offset that can be produced at the output of the Hall sensor. This makes it difficult to process the signal and maintain an accurate, reliable output over the specified temperature and voltage range. Chopper Stabilization is a unique approach used to minimize Hall offset on the chip. The Allegro patented technique, dynamic quadrature offset cancellation, removes key sources of the output drift induced by temperature and package stress. This offset reduction technique is based on a signal modulation-demodulation process. The undesired offset signal is separated from the magnetically induced signal in the frequency domain through modulation. The subsequent demodulation acts as a modulation process for the offset causing the magnetically induced signal to recover its original spectrum at baseband while the dc offset becomes a high frequency signal. Then, using a low-pass filter the signal passes while the modulated dc offset is suppressed. The chopper stabilization technique uses a 170 kHz high frequency clock. The Hall plate chopping occurs on each clock edge resulting in a 340 kHz chop frequency. The high frequency operation allows for a greater sampling that produces higher accuracy and faster signal processing capability. Using this chopper stabilization approach, the chip is desensitized to the effects of temperature and stress. The disadvantage to this approach is that jitter, also known as 360° repeatability, can be induced on the output signal. The sample and hold process used by the demodulator to store and recover the signal can slightly degrade the signal-to-noise ratio by producing replicas of the noise spectrum at the baseband causing a decrease in jitter performance. The increase in switch point performance by reducing the effects of temperature and stress, however, outweighs the degradation in the signal-to-noise ratio. This technique produces devices that have an extremely stable quiescent Hall output voltage, is immune to thermal stress, and has precise recoverability after temperature cycling. This technique is made possible through the use of a BiCMOS process which allows the use of low offset and low noise amplifiers in combination with high-density logic integration and sample and hold circuits.
Regulator
Amplifier
Sample/ Hold
CLOCK
Hall Element
Figure 1
A3425-DS Rev. 1 Page 3
Chopper-Stabilization Algorithm
115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 Copyright © 2001, 2003 Allegro MicroSystems, Inc.
A3425 ULTRA-SENSITIVE DUAL-CHANNEL QUADRATURE BIPOLAR SWITCH
FUNCTIONAL BLOCK DIAGRAM
E1
E2
FUNCTIONAL BLOCK DIAGRAM DESCRIPTION
· · · · · · · · Pin 1 connected from power supply to on-chip voltage regulator. Pin 2 connected to Output A, the output from the first Schmitt circuit. Pin 3 connected to Output B, the output from the second Schmitt circuit. Pin 4 connected to ground. Pin 5 no connection. Pin 6 no connection. Pin 7 no connection. Pin 8 no connection.
A3425-DS Rev. 1 Page 4
115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 Copyright © 2001, 2003 Allegro MicroSystems, Inc.
A3425 ULTRA-SENSITIVE DUAL-CHANNEL QUADRATURE BIPOLAR SWITCH
TYPICAL APPLICATIONS OPERATION
Magnetic Field Sensor A
Magnetic Field Sensor B
Output Sensor A
Output Sensor B
·
Output Sensor A and Output Sensor B have a phase difference of 90° with a properly designed magnet possessing a pole pitch equal to twice the 1.0 mm sensor spacing.
A3425-DS Rev. 1 Page 5
115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 Copyright © 2001, 2003 Allegro MicroSystems, Inc.
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