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A3250 and A3251
Field-Programmable, Chopper-Stabilized Unipolar Hall-Effect Switches
The A3250 and A3251 are field-programmable, chopper-stabilized, unipolar Halleffect switches designed for use in high-temperature applications. These devices use a chopper-stabilization technique to eliminate offset inherent in single-element devices. Package UA, 3-pin SIP The A3250 and A3251 are externally programmable devices. The devices have a wide range of programmability of the magnetic operate point (BOP) while the hysteresis remains fixed. This advanced feature allows for optimization of the sensor switchpoint and can drastically reduce the effects of variations found in a production environment, such as magnet and device placement tolerances. These devices provide on-chip transient protection. A Zener clamp on the power supply protects against overvoltage conditions on the supply line. These devices also include short-circuit protection on the output. The output of the A3250 switches LOW when subjected to a south-polarity magnetic field with a flux density that exceeds the threshold for BOP , and switches HIGH when the field drops below the magnetic release point, BRP . The output of the A3251 has the opposite polarity, switching HIGH in a south-polarity magnetic field that BOP , and switching LOW when the field drops below BRP . The other differences in the devices are the power-on state. The A3250 powers-on in the HIGH state, while the A3251 powers-on in the LOW state. These devices are available in a TO-92 three-lead ultra-mini SIP (Single In-line Package), with either straight or formed and trimmed lead configuration.
TL Option
1
2
3
1. VCC 2. GND 3. VOUT
Features and Benefits
ABSOLUTE MAXIMUM RATINGS
Supply Voltage, VCC ...................................... 26.5 V Reverse-Supply Voltage, VRCC ........................ -18 V Zener Overvoltage, VZ ....................................... 30 V Output Current, IOUT .........................................20 mA Magnetic Flux Density, B .........................Unlimited Operating Temperature Ambient, TA, Range J................. -40C to 115C Ambient, TA, Range L................ -40C to 150C Maximum Junction, TJ(max)........................165C Storage Temperature, TS .................. -65C to 170C Chopper stabilization for stable switchpoints throughout operating temperature range Externally programmable operate point (through VCC pin) On-board voltage regulator for 4.2 V to 24 V operation On-chip protection against: Supply transients Output short-circuits Reverse-battery condition
Use the following complete part numbers when ordering:
Part Number A3250JUA A3250JUATL A3250LUA A3250LUATL A3251JUA A3251JUATL A3251LUA A3251LUATL Package Straight lead Formed lead Straight lead Formed lead Straight lead Formed lead Straight lead Formed lead TA (C) -40 to 115 -40 to 150 -40 to 115 -40 to 150 VOUT Bhys(typ) (G) Power-On Running* 18 High 13 18 Low 13 High Low
*In south polarity magnetic field of sufficient strength.
A3250-DS
Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com
A3250 and A3251
Field-Programmable, Chopper-Stabilized, Unipolar Hall-Effect Switches
Functional Block Diagram
VCC
Program/Lock Programming Logic
Regulator
Offset Adjust Sample and Hold Dynamic Offset Cancellation VOUT
Amp
Current Limit Low-Pass Filter
GND
Hysteresis Curves
A3250
Hysteresis of VOUT Switching Due to B VOUT(off)
A3251
Hysteresis of VOUT Switching Due to B VOUT(off)
V+
V+
Switch to High
Switch to High
Switch to Low
Switch to Low
VOUT
VOUT
VOUT(on)(sat)
VOUT(on)(sat)
BRP
BHYS
BHYS
Output voltage in relation to sensed magnetic flux density in a south polarity magnetic field of sufficient strength. Transition through BOP must precede transition through BRP.
Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com
BOP
B+
B+
BRP
BOP
2
A3250-DS
A3250 and A3251
Field-Programmable, Chopper-Stabilized, Unipolar Hall-Effect Switches
OPERATING CHARACTERISTICS valid over operating TA and VCC, unless otherwise specified Characteristic ELECTRICAL CHARACTERISTICS Supply Voltage1 Output Saturation Voltage Output Leakage Current VCC VOUT(sat) IOFF ICC(off) Supply Current ICC(on) Output Rise Time Output Fall Time Chopping Frequency Power-Up Time Output Current Limit1,2 tr tf fC ton IOUT(lim) POS VOUT = HIGH Short-circuit protection A3250; B < BRP, t > ton A3251; B < BRP, t > ton Running mode IOUT = 20 mA; Switch state = ON VOUT = 24 V; Switch state = OFF A3250; B < BRP; VOUT = HIGH A3251; B > BOP; VOUT = HIGH A3250; B > BOP; VOUT = LOW A3251; B < BRP; VOUT = LOW RLOAD = 820 , CLOAD = 10 pF RLOAD = 820 , CLOAD = 10 pF 4.2 - - - - - - - - - - 60 - - - 175 - 4.0 4.0 6.0 6.0 - - 340 20 90 HIGH LOW 24 400 10 7.0 7.0 10.0 10.0 5.0 5.0 - 50 120 - - V mV A mA mA mA mA s s kHz s mA mV mV Symbol Test Conditions Min. Typ. Max. Units
Power-On State MAGNETIC CHARACTERISTICS Initial Operate Point Temperature Drift of BOP Hysteresis (BOP - BRP)
BOP BOP Bhys BOP 500 gauss Package TA range = J Package TA range = L
-20 -35 5.0 5.0
13 - 18 13
50 35 35 35
G G G G
PROGRAMMING CHARACTERISTICS Programmable BOP Values3 Number of Programming Bits Resolution BOP(prog) - BRES Switchpoint set Programming lock 50 - - - - 6 1 7.0 350 - - - G Bit Bit G
TRANSIENT PROTECTION CHARACTERISTICS Supply Zener Voltage Supply Zener Current Reverse Battery Current
1 2 3
VZ IZ IRCC VCC = 28 V VRCC = -18 V, TJ < TJ(max)
28 - -
- - -
- 13 -5.0
V mA mA
Do not exceed TJ(max): Additional information on power derating is provided in the applications section. Short-circuit protection is not intended for continuous operation; permanent damage may result. Device can be used below 50 G but is not guaranteed to be a unipolar switch. It is the responsibility of the programmer to verify that the desired switchpoint has been achieved.
A3250-DS
Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com
3
A3250 and A3251
Field-Programmable, Chopper-Stabilized, Unipolar Hall-Effect Switches Typical Characterization Data
All data are taken with A3250 devices, the average of 3 lots, 30 pieces per lot
Average BOP vs. TA Program Code: 1, VCC = 12 V 30
Average BRP vs. TA Program Code: 1, VCC = 12 V
10
Average BRP (G)
-20 10 40 70 TA (C) 100 130 160
Average BOP (G)
25 20 15 10 5 0 -5 -50
5 0 -5 -10 -15 -20 -50 -20 10 40 70 TA (C) 100 130 160
Average BOP vs. TA Program Code: 8, VCC = 12 V
75
Average BRP vs. TA Program Code: 8, VCC = 12 V
60
Average BOP (G)
Average BRP (G)
70 65 60 55 50 45 40 -50 -20 10 40 70 TA (C) 100 130 160
50 40 30 20 -50
-20
10
40 70 TA (C)
100
130
160
Average BOP vs. TA Program Code: 16, VCC = 12 V
130
Average BRP vs. TA Program Code: 16, VCC = 12 V
110
Average BOP (G)
125 120 115 110 105 100 -50 -20 10 40 70 TA (C) 100 130 160
Average BRP (G)
105 100 95 90 85 80 -50 -20 10 40 70 TA (C) 100 130 160
A3250-DS
Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com
4
A3250 and A3251
Field-Programmable, Chopper-Stabilized, Unipolar Hall-Effect Switches Typical Characterization Data
All data are taken with A3250 devices, the average of 3 lots, 30 pieces per lot
Average B hys vs. Temperature Program Code: 1, VCC = 12 V 35
Average BHYS (G)
Average B hys vs. Temperature Program Code: 16, VCC = 12 V 35
Average BHYS (G)
30 25 20 15 10 5 0 -50 -20 10 40
TA (C)
30 25 20 15 10 5 0 -50 -20 10 40 70 TA (C) 100 130 160
70
100
130
160
Average B hys vs. Temperature Program Code: 8, VCC = 12 V
30
Average BOP vs. Temperature -40C to 25C and 150C to 25C
20 10 0
Code 1 Code 8 Code 16
35
Average BHYS (G)
30 25 20 15 10 5 0 -50 -20 10 40
TA (C)
70
100
130
160
Average BOP (G)
-10 -20 -30 -40C to 25C
150C to 25C
TA (C)
A3250-DS
Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com
5
A3250 and A3251
Field-Programmable, Chopper-Stabilized, Unipolar Hall-Effect Switches Typical Characterization Data
All data are taken with A3250 devices, the average of 3 lots, 30 pieces per lot
Average ICC(on) vs. Temperature 10 8
10 8
Average ICC(off) vs. Temperature
ICC(off) @ 3.8 V ICC(off) @ 12.0 V ICC(off) @ 26.5 V
ICC(on) (mA)
6 4 2 0 -50 -20 10 40 70
ICC(on) @ 3.8 V ICC(on) @ 12.0 V ICC(on) @ 26.5 V
ICC(off) (mA)
160
6 4 2 0 -50 -20 10 40 70
100
130
100
130
160
TA (C)
TA (C)
Average VOUT(SAT) vs. Temperature VCC = 3.8 V, Iout = 20 mA 280 260 240 220 200 180 160 140 -50 -20 10 40 70 100 130 160
VOUT(SAT) (mV)
TA (C)
A3250-DS
Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com
6
A3250 and A3251
Field-Programmable, Chopper-Stabilized, Unipolar Hall-Effect Switches
THERMAL CHARACTERISTICS may require derating at maximum conditions, see application information
Characteristic Package Thermal Resistance Symbol RJA Test Conditions Package UA, minimum-K PCB (single-sided with copper limited to solder pads) Min. 165 Typ. - Max Units - C/W
25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 20 40
Power Derating Curve TJ(max) = 165C; ICC = ICC(max)
VCC(max)
Maximum Allowable VCC (V)
Minimum-K PCB, Package UA (RJA = 165 C/W)
VCC(min)
60
80
100
120
140
160
180
1900 1800 1700 1600 1500 1400 1300 1200 1100 1000 900 800 700 600 500 400 300 200 100 0 20
Maximum Power Dissipation, PD(max) TJ(max) = 165C; VCC = VCC(max); ICC = ICC(max)
Power Dissipation, PD (m W)
Min (R imum -K JA = 165 PCB C/ , Pac W) ka
ge
UA
40
60
80 100 120 Temperature (C)
140
160
180
A3250-DS
Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com
7
A3250 and A3251
Field-Programmable, Chopper-Stabilized, Unipolar Hall-Effect Switches
Functional Description
Chopper-Stabilized Technique The Hall sensor is based on a Hall element, a small sheet of semiconductor material in which a constant bias current flows when a constant voltage source is applied. The output takes the form of a voltage measured across the width of the Hall element, and has negligible value in the absence of a magnetic field. When a magnetic field is applied with flux lines at right angles to the current in the Hall element, a small signal voltage directly proportional to the strength of the magnetic field occurs at the output of the Hall element. This small signal voltage is disproportionally small relative to the offset produced at the input of the device. This makes it very difficult to process the signal and maintain an accurate, reliable output over the specified temperature and voltage range. Therefore, it is important to reduce any distortion of the signal that could be amplified when the signal is processed. Chopper stabilization is a unique approach used to minimize input offset on the Hall IC. This technique removes a key source of output drift due to temperature and mechanical stress, and produces a 3X reduction in offset in comparison to other, conventional methods. This offset reduction chopping technique is based on a signal modulation-demodulation process. The undesired offset signal is separated from the magnetically-induced signal in the frequency domain. The offset (and any low-frequency noise) component of the signal can be seen as signal distortion added after the signal modulation process has taken place. Therefore, the dc offset is not modulated and remains a low-frequency component. Consequently, the signal demodulation process acts as a modulation process for the offset, causing the magneticallyinduced signal to recover its original spectrum at baseband while the dc offset becomes a high-frequency signal. Then, the signal passes using a low-pass filter, while the modulated dc offset is suppressed. The advantage of this approach is significant offset reduction, which desensitizes the Hall IC against the effects of temperature and mechanical stress. The disadvantage is that this technique features a demodulator that uses a sample-and-hold block to store and recover the signal. This sampling process can slightly degrade the SNR (signal-to-noise ratio) by producing replicas of the noise spectrum at the baseband. This degradation is a function of the ratio between the white noise spectrum and the sampling frequency. The effect of the degradation of the SNR is higher jitter, also known as signal repeatability. However, the jitter in a continuous-time device can be 5X that of the A3250/A3251.
Regulator
Amp
Chopper stabilization circuit (dynamic quadrature offset cancellation)
Sample and Hold / LPF
A3250-DS
Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com
8
A3250 and A3251
Field-Programmable, Chopper-Stabilized, Unipolar Hall-Effect Switches
Programming Protocol The operate switchpoint, BOP , can be field-programmed. To do so, a coded series of voltage pulses through the VCC pin is used to set bitfields in onboard registers. The effect on the device output can be monitored, and the registers can be cleared and set repeatedly until the required BOP is achieved. To make the setting permanent, bitfield-level solid state fuses are blown, and finally, a device-level fuse is blown, blocking any further coding. It is not necessary to program the release switchpoint, BRP , because the difference between BOP and BRP , referred to as the hysteresis, BHYS , is fixed. The range of values between BOP(min) and BOP(max) is scaled to 64 increments. The actual change in magnetic flux (G) represented by each increment is indicated by BRES (see the Operating Characteristics table; however, testing is the only method for verifying the resulting BOP). For programming, the 64 increments are individually identified using 6 data bits, which are physically represented by 6 bitfields in the onboard registers. By setting these bitfields, the corresponding calibration value is programmed into the device. Three voltage levels are used in programming the device: a low voltage, VPL , a minimum required to sustain register settings; a mid-level voltage, VPM , used to increment the address counter in the device; and a high voltage, VPH , used to separate sets of VPM pulses (when short in duration) and to blow fuses (when long in duration). A fourth voltage level, essentially 0 V, is used to clear the registers between pulse sequences. The pulse values are shown in the Programming Protocol Characteristics table and in figure 1.
VPH V+
VPM
VPL Td(P) 0 Td(0) Td(1) t
Figure 1. Pulse amplitudes and durations
Additional information on device programming and programming products is available on www. allegromicro.com. Programming hardware is available for purchase, and programming software is available free of charge.
Code Programming. Each bitfield must be individually set. To
do so, a pulse sequence must be transmitted for each bitfield that is being set to 1. If more than one bitfield is being set to 1, all pulse sequences must be sent, one after the other, without allowing VCC to fall to zero (which clears the registers). The same pulse sequence is used to provisionally set bitfields as is used to permanently set bitfield-level fuses. The only difference is that when provisionally setting bitfields, no fuse-blowing pulse is sent at the end of the pulse sequence.
PROGRAMMING PROTOCOL CHARACTERISTICS, TA = 25C, unless otherwise noted Characteristic Symbol VPL Programming Voltage1 VPM VPH Programming Current2 IPP td(0) Pulse Width td(1) td(P) Pulse Rise Time Pulse Fall Time
1Programming 2A bypass
Test Conditions Minimum voltage range during programming
Min. 4.5 10 23
Typ. 5.0 11 25 500 - - 300 - -
Max. 5.5 12 26 - - - - - -
Units V V V mA s s s s s
Maximum supply current during programming OFF time between programming bits Pulse duration (ON time) for enable, address, fuse blowing or lock bits Pulse duration (ON time) for fuse blowing VPL to VPM; VPL to VPH VPM to VPL; VPH to VPL
- 20 20 100 11 5
tr tf
voltages are measured at the VCC pin. capacitor with a minimum capacitance of 0.1 F must be connected from VCC to the GND pin of the device in order to provide the current necessary to blow the fuse.
Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com
9
A3250-DS
A3250 and A3251
Field-Programmable, Chopper-Stabilized, Unipolar Hall-Effect Switches
The pulse sequences consist of the following groups of pulses: 1. An enable sequence. 2. A bitfield address sequence. 3. When permanently setting the bitfield, a long VPH fuse-blowing pulse. (Note: Blown bit fuses cannot be reset.) When provisionally trying a value, a short VPH pulse. 4. When permanently setting the bitfield, the level of VCC must be allowed to drop to zero between each pulse sequence, in order to clear all registers. However, when provisionally setting bitfields, VCC must be maintained at VPL between pulse sequences, in order to maintain the prior bitfield settings while preparing to set additional bitfields. Bitfields that are not set are evaluated as zeros. The bitfield-level
V+ VPH
fuses for 0 value bitfields are never blown. This prevents inadvertently setting the bitfield to 1. Instead, blowing the devicelevel fuse protects the 0 bitfields from being accidentally set in the future. Two pulse sequences for provisionally trying the calibration value 5 are shown in figure 2. Because the bitfields must be set individually, 510 must be programmed as binary 101. Bit 3 is set to 1 (0001002, which is 410), then bit 1 is set to 1 (0000012, which is 110). Bit 2 is ignored, and so remains 0. Two pulse sequences for permanently setting the calibration value 5 are shown in figure 3. The final VPH pulse, which was used as a short delimiter when trying values, is maintained for a longer period, enough to blow the corresponding bitfield-level fuse.
VPM
VPL 7 pulses 0 Enable Try 001002 (410) Address Optional Monitoring Enable Try 000012 (110) Optional Clear Monitoring t 7 pulses Address
Figure 2. Pulse sequence to provisionally try calibration value 5 (101 binary, or bitfield address 3 and bitfield address 1).
V+ VPH
VPM
VPL 7 pulses 0 Enable Address Encode 001002 (410) Blow Enable Blow 7 pulses Address
Encode 000012 (110) t
Figure 3. Pulse sequence to permanently encode calibration value 5 (101 binary, or bitfield address 3 and bitfield address 1).
A3250-DS
Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com
10
A3250 and A3251
Field-Programmable, Chopper-Stabilized, Unipolar Hall-Effect Switches
V+ VPH
Enabling Addressing Mode. The first segment of code is a keying sequence used to enable the bitfield addressing mode. As shown in figure 4, this segment consists of one short VPH pulse, seven or more VPM pulses, and one VPH pulse, with no supply interruptions. This sequence is designed to prevent the device from being programmed accidentally, such as by noise on the supply line.
VPM
VPL
0
Minimum 7 pulses
t
Figure 4. Addressing mode enable pulse sequence
V+ VPH
Address Selection. After addressing mode is enabled, the
target bitfield address, is indicated by a series of VPM pulses, as shown in figure 3. When provisionally trying a value, this sequence is followed by a short VPH pulse, which serves to delimit the address and set the corresponding bitfield. When permanently setting a bitfield, the VPH pulse is continued for a longer period of time, suffienct to not only set the bitfield to 1, but also to blow the bitfield fuse.
Address 1 Address 2 Address n ( 63)
VPM
VPL
0
t
Figure 5. Pulse sequence to select addresses
V+ Falling edge of final BOP address digit VPH
Lock Bit Programming. After the desired BOP calibration value
is programmed, and all of the corresponding bitfield-level fuses are blown, the device-level fuse should be blown. To do so, the lock bit (bitfield address 65) should be encoded as 1 and have its fuse blown. This is done in the same manner as permanently setting the other bitfields, as shown in figure 6.
VPM
VPL 7 pulses 0 Enable Address Encode Lock Bit Blow 65 pulses
Figure 6. Pulse sequence to encode lock bit
t
A3250-DS
Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com
11
A3250 and A3251
Field-Programmable, Chopper-Stabilized, Unipolar Hall-Effect Switches Application Information
For additional general application information, visit the Allegro MicroSystems Web site at www. allegromicro.com. Typical Application Circuit It is strongly recommended that an external ceramic bypass capacitor, CBYP, in the range of 0.01 F to 0.1 F be connected between the VCC pin and the supply and GND pin to reduce both external noise and noise generated by the chopper-stabilization technique. (The diagram at the right shows CBYP at 0.1 F.) CBYP should be installed so that the traces that connect it to the A3250/A3251 are no greater than 5 mm in length. The series resistor RS, in combination with CBYP creates a filter for EMI pulses. (Additional information on EMC is provided on the Allegro MicroSystems Web site.) RS will have a drop of approximately 800 mV. This must be taken into consideration when determining the minimum VCC requirement for the A3250/A3251. The pull-up resistor, RL, should be chosen to limit the current through the output transistor; do not exceed the maximum continuous output current of the device.
RS 100 A
5V
VCC
RL 1.2 k VOUT
VSupply
CBYP 0.1 F
A3250/A3251
GND A
A
Maximum separation 5 mm from CBYP to device
Typical application circuit
A3250-DS
Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com
12
A3250 and A3251
Field-Programmable, Chopper-Stabilized, Unipolar Hall-Effect Switches
Power Derating The device must be operated below the maximum junction temperature of the device, TJ(max). Under certain combinations of peak conditions, reliable operation may require derating supplied power or improving the heat dissipation properties of the application. This section presents a procedure for correlating factors affecting operating TJ. (Thermal data is also available on the Allegro MicroSystems Web site.) The Package Thermal Resistance, RJA, is a figure of merit summarizing the ability of the application and the device to dissipate heat from the junction (die), through all paths to the ambient air. Its primary component is the Effective Thermal Conductivity, K, of the printed circuit board, including adjacent devices and traces. Radiation from the die through the device case, RJC, is relatively small component of RJA. Ambient air temperature, TA, and air motion are significant external factors, damped by overmolding. The effect of varying power levels (Power Dissipation, PD), can be estimated. The following formulas represent the fundamental relationships used to estimate TJ, at PD. PD = VIN x IIN T = PD x RJA TJ = TA + T (1) (2) (3) Example: Reliability for VCC at TA = 150C, package UA, using minimum-K PCB. Observe the worst-case ratings for the device, specifically: RJA = 165C/W, TJ(max) = 165C, VCC(max) = 24 V, and ICC(max) = 10 mA. Calculate the maximum allowable power level, PD(max). First, invert equation 3: Tmax = TJ(max) - TA = 165 C - 150 C = 15 C This provides the allowable increase to TJ resulting from internal power dissipation. Then, invert equation 2: PD(max) = Tmax / RJA = 15C / 165 C/W = 91 mW Finally, invert equation 1 with respect to voltage: VCC(est) = PD(max) / ICC(max) = 91 mW / 10 mA = 9 V The result indicates that, at TA, the application and device can dissipate adequate amounts of heat at voltages VCC(est). Compare VCC(est) to VCC(max). If VCC(est) VCC(max), then reliable operation between VCC(est) and VCC(max) requires enhanced RJA. If VCC(est) VCC(max), then operation between VCC(est) and VCC(max) is reliable under these conditions.
For example, given common conditions such as: TA= 25C, VCC = 12 V, ICC = 4 mA, and RJA = 165 C/W, then: PD = VCC x ICC = 12 V x 4 mA = 48 mW T = PD x RJA = 48 mW x 165 C/W = 8C TJ = TA + T = 25C + 8C = 33C A worst-case estimate, PD(max), represents the maximum allowable power level (VCC(max), ICC(max)), without exceeding TJ(max), at a selected RJA and TA.
A3250-DS
Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com
13
A3250 and A3251
Field-Programmable, Chopper-Stabilized, Unipolar Hall-Effect Switches
Package UA, 3-Pin; (TO-92)
The products described herein are manufactured under one or more of the following U.S. patents: 5,045,920; 5,264,783; 5,442,283; 5,389,889; 5,581,179; 5,517,112; 5,619,137; 5,621,319; 5,650,719; 5,686,894; 5,694,038; 5,729,130; 5,917,320; and other patents pending. Allegro MicroSystems, Inc. reserves the right to make, from time to time, such departures from the detail specifications as may be required to permit improvements in the performance, reliability, or manufacturability of its products. Before placing an order, the user is cautioned to verify that the information being relied upon is current. Allegro products are not authorized for use as critical components in life-support devices or systems without express written approval. The information included herein is believed to be accurate and reliable. However, Allegro MicroSystems, Inc. assumes no responsibility for its use; nor for any infringement of patents or other rights of third parties which may result from its use. Copyright (c) 2004 Allegro MicroSystems, Inc.
Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com
14
A3250-DS
A3250 and A3251
Field-Programmable, Chopper-Stabilized, Unipolar Hall-Effect Switches
A3250-DS
Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com
15

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