Description
The Allegro® A1205 Hall-effect bipolar switch is a next-
generation replacement and extension of the popular Allegro
A3134 bipolar switch. The A1205 has identical specifications
as the A1201 but is recommended for applications that require
pulsing VCC to conserve power. For standard applications,
where VCC is constant, please refer to the A1201 through
A1204 devices.
Overall, the A120x family, produced with BiCMOS technology,
consists of continuous-time devices that feature fast power-
on time and low-noise operation. Device programming is
performed after packaging to ensure increased switchpoint
accuracy by eliminating offsets that can be induced by
package stress. Unique Hall element geometries and low-
offset amplifiers help to minimize noise and to reduce the
residual offset voltage normally caused by device overmolding,
temperature excursions, and thermal stress.
The A120x Hall-effect bipolar switches include the following on
a single silicon chip: voltage regulator, Hall-voltage generator,
small-signal amplifier, Schmitt trigger, and NMOS output
transistor. The integrated voltage regulator permits operation
from 3.8 to 24 V. The extensive on-board protection circuitry
A12051-DS, Rev. 6
Features and Benefits
▪ Ideal for applications that require pulsing VCC to
conserve power
▪ Continuous-time operation
▫ Fast power-on time
▫ Low noise
▪ Stable operation over full operating temperature range
▪ Reverse battery protection
▪ Solid-state reliability
▪ Factory-programmed at end-of-line for optimum
performance
▪ Robust EMC performance
▪ High ESD rating
▪ Regulator stability without a bypass capacitor
Continuous-Time Bipolar Switch
Continued on the next page…
Packages:
Functional Block Diagram
Not to scale
A1205
3 pin SOT23W (LH)
3 pin SIP (UA)
Amp
Regulator
GND
VCC
VOUT
OffsetGain
Trim
Control
To all subcircuits
Continuous-Time Bipolar Switch
A1205
2
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
Selection Guide
Part Number Packing* Mounting Ambient, TABRP (Min) BOP (Max)
A1205LLHLT-T 7-in. reel, 3000 pieces/reel 3-pin SOT23W surface mount –40ºC to 150ºC –50 50
A1205LUA-T Bulk, 500 pieces/bag 3-pin SIP through hole
*Contact Allegro for additional packing options.
Description (continued)
Absolute Maximum Ratings
Characteristic Symbol Notes Rating Units
Supply Voltage VCC 30 V
Reverse Supply Voltage VRCC –30 V
Output Off Voltage VOUT 30 V
Reverse Output Voltage VROUT –0.5 V
Output Current Sink IOUTSINK 25 mA
Magnetic Flux Density BUnlimited G
Operating Ambient Temperature TA
Range E –40 to 85 ºC
Range L –40 to 150 ºC
Maximum Junction Temperature TJ(max) 165 ºC
Storage Temperature Tstg –65 to 170 ºC
makes possible a ±30 V absolute maximum voltage rating for superior
protection in automotive and motor commutation applications,
without adding external components.
The small geometries of the BiCMOS process allow these devices
to be provided in ultrasmall packages. The package styles available
provide magnetically optimized solutions for most applications.
Package LH is a SOT23W miniature thin-profile surface-mount
package, while package UA is a three-lead ultramini SIP for through-
hole mounting. Each package is lead (Pb) free, with 100% matte
tin plated leadframes.
Continuous-Time Bipolar Switch
A1205
3
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
OPERATING CHARACTERISTICS over full operating voltage and ambient temperature ranges, unless otherwise noted
Characteristic Symbol Test Conditions Min. Typ. Max. Units
Electrical Characteristics
Supply Voltage1VCC Operating, TJ < 165°C 3.8 – 24 V
Output Leakage Current IOUTOFF VOUT = 24 V, B < BRP ––10A
Output On Voltage VOUT(SAT) IOUT = 20 mA, B > BOP – 215 400 mV
Power-On Time2tPO
Slew rate (dVCC/dt) < 2.5 V/s, B > BOP + 5 G or
B < BRP – 5 G ––4s
Output Rise Time3trVCC = 12 V, RLOAD = 820 , CS = 12 pF – – 200 ns
Output Fall Time3tfVCC = 12 V, RLOAD = 820 , CS = 12 pF – – 200 ns
Supply Current ICCON B > BOP – 3.8 7.5 mA
ICCOFF B < BRP – 3.5 7.5 mA
Reverse Battery Current IRCC VRCC = –30 V – – –10 mA
Supply Zener Clamp Voltage VZICC = 30 mA; TA = 25°C 32 – 40 V
Supply Zener Current IZVZ = 32 V; TA = 25°C – – 30 mA
Magnetic Characteristics4
Operate Point BOP South pole adjacent to branded face of device –40 15 50 G
Release Point BRP North pole adjacent to branded face of device –50 –15 40 G
Hysteresis BHYS BOP – BRP 53055G
1 Maximum voltage must be adjusted for power dissipation and junction temperature, see Power Derating section.
2 For VCC slew rates greater than 2.5 V/s, and TA = 150°C, the Power-On Time can reach its maximum value.
3 CS =oscilloscope probe capacitance.
4 Magnetic flux density, B, is indicated as a negative value for north-polarity magnetic fields, and as a positive value for south-polarity magnetic fields.
This so-called algebraic convention supports arithmetic comparison of north and south polarity values, where the relative strength of the field is indicated
by the absolute value of B, and the sign indicates the polarity of the field (for example, a –100 G field and a 100 G field have equivalent strength, but
opposite polarity). Reference to the magnetic field polarity is with respect to the beveled face of the device.
DEVICE QUALIFICATION PROGRAM
Contact Allegro for information.
EMC (Electromagnetic Compatibility) REQUIREMENTS
Contact Allegro for information.
Continuous-Time Bipolar Switch
A1205
4
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
THERMAL CHARACTERISTICS may require derating at maximum conditions, see application information
Characteristic Symbol Test Conditions* Value Units
Package Thermal Resistance RθJA
Package LH, 1-layer PCB with copper limited to solder pads 228 ºC/W
Package LH, 2-layer PCB with 0.463 in.2 of copper area each side
connected by thermal vias 110 ºC/W
Package UA, 1-layer PCB with copper limited to solder pads 165 ºC/W
*Additional thermal information available on Allegro Web site.
6
7
8
9
2
3
4
5
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
20 40 60 80 100 120 140 160 180
Maximum Allowable V
CC
(V)
TJ(max) = 165ºC; ICC = ICC(max)
(R
JA
= 228 ºC/W)
Package LH, 1-layer PCB
(R
JA
= 110 ºC/W)
Package LH, 2-layer PCB
(R
JA
= 165 ºC/W)
Package UA, 1-layer PCB
V
CC(min)
V
CC(max)
0
100
200
300
400
500
600
700
800
900
1000
1100
1200
1300
1400
1500
1600
1700
1800
1900
20 40 60 80 100 120 140 160 180
Temperature (°C)
Power Dissipation, P
D
(mW)
Power Dissipation versus Ambient Temperature
(R
θJA
= 165 ºC/W)
1-layer PCB, Package UA
(RθJA = 228 ºC/W)
1-layer PCB, Package LH
(RθJA = 110 ºC/W)
2-layer PCB, Package LH
Continuous-Time Bipolar Switch
A1205
5
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
Characteristic Data
–50 0 50 100 150
0 5 10 15 20 25
–50 0 50 100 150
0 5 10 15 20 25
0
50
100
150
200
250
300
350
–50 0 50 100 150
0 5 10 15 20 25
0
50
100
150
200
250
300
350
T
A
(°C)
Supply Current (On) versus Ambient Temperature
VCC (V)
ICCON (mA)
24
3.8
T
A
(°C)
Supply Current (Off) versus Ambient Temperature
VCC (V)
ICCOFF (mA)
24
3.8
I
LOAD
= 20 mA I
LOAD
= 20 mA
T
A
(°C)
Output Voltage (On) versus Ambient Temperature
VCC (V)
VOUT(SAT) (mV)
24
3.8
Supply Current (On) versus Supply Voltage
TA (°C)
ICCON (mA)
V
CC
(V)
–40
25
150
Supply Current (Off) versus Supply Voltage
TA (°C)
ICCOFF (mA)
V
CC
(V)
–40
25
150
Output Voltage (On) versus Supply Voltage
TA (°C)
VOUT(SAT) (mV)
V
CC
(V)
–40
25
150
0
1.0
2.0
3.0
4.0
5.0
7.0
6.0
8.0
0
1.0
2.0
3.0
4.0
5.0
7.0
6.0
8.0
0
1.0
2.0
3.0
4.0
5.0
7.0
6.0
8.0
0
1.0
2.0
3.0
4.0
5.0
7.0
6.0
8.0
Continuous-Time Bipolar Switch
A1205
6
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
T
A
(°C)
–40
25
150
Supply Voltage (V)
0 5 10 15 20 25 25
Hysteresis versus Supply Voltage
15
10
5
20
25
30
35
40
45
50
55
BHYS (G )
Hysteresis versus Ambient Temperature
B
HYS
(G )
T
A
(°C)
–50 0 50 100 150
55
50
45
40
35
30
25
20
15
10
5
V
CC
(V)
24
12
3.8
T
A
(°C)
–40
25
150
Supply Voltage (V)
0 5 10 15 20 25 25
Release Point versus Supply Voltage
-40
-50
-30
-20
-10
0
10
20
30
40
BRP (G )
Operate Point versus Ambient Temperature
B
OP
(G )
T
A
(°C)
–50 0 50 100 150
V
CC
(V)
24
12
3.8
Release Point versus Ambient Temperature
B
RP
(G )
T
A
(°C)
–50 0 50 100 150
40
30
20
10
0
–10
–20
–30
–40
–50
V
CC
(V)
24
12
3.8
T
A
(°C)
–40
25
150
Supply Voltage (V)
0 5 10 15 20 25 25
Operate Point versus Supply Voltage
-40
-30
-20
-10
0
10
20
30
40
50
BOP (G )
Operate Point versus Ambient Temperature
B
OP
(G )
T
A
(°C)
–50 0 50 100 150
50
40
30
20
10
0
–10
–20
–30
–40
V
CC
(V)
24
12
3.8
Continuous-Time Bipolar Switch
A1205
7
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
Functional Description
Bipolar Device Switching
The devices of the A120X family provide highly sensitive
switching for applications using magnetic fields of alternating
polarities, such as ring magnets. There are three switching modes
for bipolar devices, referred to as latch, unipolar switch, and
negative switch. Mode is determined by the switchpoint charac-
teristics of the individual device. The characteristic hysteresis,
BHYS , of the device, is the difference in the relative magnetic
strength and polarity of the switchpoints of the device. (Note
that, in the following descriptions, a negative magnetic value
indicates a north polarity field, and a positive magnetic value
indicates a south polarity field. For a given value of magnetic
strength, BX , the values –BX and BX indicate two fields of equal
strength, but opposite polarity. B = 0 indicates the absence of a
magnetic field.)
Bipolar devices typically behave as latches. In this mode,
magnetic fields of opposite polarity and equivalent strengths
are needed to switch the output. When the magnetic fields are
removed (B 0) the device remains in the same state until a
magnetic field of the opposite polarity and of sufficient strength
causes it to switch. The hysteresis of latch mode behavior is
shown in panel A of figure 1.
In contrast to latching, when a device exhibits unipolar switch-
ing, it only responds to a south magnetic field. The field must
be of sufficient strength, > BOP , for the device to operate. When
the field is reduced beyond the BRP level, the device switches
back to the high state, as shown in panel B of figure 1. Devices
exhibiting negative switch behavior operate in a similar but
opposite manner. A north polarity field of sufficient strength,
> BRP
, (more north than BRP) is required for operation, although
the result is that VOUT switches high, as shown in panel C. When
Figure 1. Bipolar Device Output Switching Modes. These behaviors can be exhibited when using a circuit such as that shown in panel D. Panel A
displays the hysteresis when a device exhibits latch mode (note that the BHYS band incorporates B= 0), panel B shows unipolar switch behavior (the
BHYS band is more positive than B = 0), and panel C shows negative switch behavior (the BHYS band is more negative than B = 0). Bipolar devices,
such as the 120x family, can operate in any of the three modes.
BOP
BRP
BHYS
VOUT
VOUT(SAT)
Switch to Low
Switch to High
V+
0
BOP
BRP
BHYS
VOUT
VOUT(SAT)
Switch to Low
Switch to High
V+
0
BOP
BRP
BHYS
VOUT
VOUT(SAT)
Switch to Low
Switch to High
V+
0
VCC VCC VCC
B+B– B+B– 0
0B+B– 0
(A) (B) (C)
VCC
VS
Output
GND
VOUT
RL
A120x
(D)
Continuous-Time Bipolar Switch
A1205
8
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
the field is reduced beyond the BOP level, the device switches
back to the low state.
The typical output behavior of the A120x devices is latching.
However, the A120x family is designed to attain a small hys-
teresis, and thereby provide more sensitive switching. Although
this means that true latching behavior cannot be guaranteed in all
cases, proper switching can be ensured by use of both south and
north magnetic fields, as in a ring magnet. The hysteresis of the
A120x family allows clean switching of the output, even in the
presence of external mechanical vibration and electrical noise.
Bipolar devices adopt an indeterminate output state when pow-
ered-on in the absence of a magnetic field or in a field that lies
within the hysteresis band of the device.
For more information on Bipolar switches, refer to Application
Note 27705, Understanding Bipolar Hall Effect Sensor ICs.
CONTINUOUS-TIME BENEFITS
Continuous-time devices, such as the A120x family, offer the
fastest available power-on settling time and frequency response.
Due to offsets generated during the IC packaging process, contin-
uous-time devices typically require programming after packaging
to tighten magnetic parameter distributions. In contrast, chop-
per-stabilized switches employ an offset cancellation technique
on the chip that eliminates these offsets without the need for
after-packaging programming. The tradeoff is a longer settling
time and reduced frequency response as a result of the chopper-
stabilization offset cancellation algorithm.
The choice between continuous-time and chopper-stabilized
designs is solely determined by the application. Battery manage-
ment is an example where continuous-time is often required. In
these applications, VCC is chopped with a very small duty cycle
in order to conserve power (refer to figure 2). The duty cycle
is controlled by the power-on time, tPO, of the device. Because
Figure 2. Continuous-Time Application, B < BRP.. This figure illustrates the use of a quick cycle for chopping VCC in order to conserve battery power.
Position 1, power is applied to the device. Position 2, the output assumes the correct state at a time prior to the maximum Power-On Time, tPO(max).
The case shown is where the correct output state is HIGH . Position 3, tPO(max) has elapsed. The device output is valid. Position 4, after the output is
valid, a control unit reads the output. Position 5, power is removed from the device.
VCC
VOUT
Output Sampled
1 5 4
2
t
t
t
PO(max)
3
Continuous-Time Bipolar Switch
A1205
9
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
continuous-time devices have the shorter power-on time, they are
the clear choice for such applications.
For more information on the chopper stabilization technique,
refer to Technical Paper STP 97-10, Monolithic Magnetic Hall
Sensing Using Dynamic Quadrature Offset Cancellation and
Technical Paper STP 99-1, Chopper-Stabilized Amplifiers with a
Track-and-Hold Signal Demodulator.
ADDITIONAL APPLICATIONS INFORMATION
Extensive applications information for Hall-effect devices is
available in:
• Hall-Effect IC Applications Guide, Application Note 27701
• Hall-Effect Devices: Gluing, Potting, Encapsulating, Lead
Welding and Lead Forming, Application Note 27703.1
• Soldering Methods for Allegro’s Products – SMT and Through-
Hole, Application Note 26009
All are provided in Allegro Electronic Data Book, AMS-702, and
the Allegro Web site, www.allegromicro.com.
Pin-out Diagrams
Terminal List
Name Description Number
Package LH Package UA
VCC Connects power supply to chip 1 1
VOUT Output from circuit 2 3
GND Ground 3 2
1
3
2
GND
VOUT
VCC
Package UAPackage LH
1
2
3
GND
VOUT
VCC
Continuous-Time Bipolar Switch
A1205
10
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
Power Derating
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 sup-
plied 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 sum-
marizing 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 × IIN (1)
T = PD × RJA (2)
TJ = TA + ΔT (3)
For example, given common conditions such as: TA= 25°C,
VCC = 12 V, ICC = 4 mA, and RJA = 140 °C/W, then:
P
D = VCC × ICC = 12 V × 4 mA = 48 mW
T = PD × RJA = 48 mW × 140 °C/W = 7°C
T
J = TA + T = 25°C + 7°C = 32°C
A worst-case estimate, PD(max), represents the maximum allow-
able power level (VCC(max), ICC(max)), without exceeding TJ(max),
at a selected RJA and TA.
Example: Reliability for VCC at TA =
150°C, package UA, using
minimum-K PCB.
Observe the worst-case ratings for the device, specifically:
RJA
=
165°C/W, TJ(max) =
165°C, VCC(max)
= 24 V, and
ICC(max) = 7.5 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 = 15°C ÷ 165 °C/W = 91 mW
Finally, invert equation 1 with respect to voltage:
VCC(est) = PD(max) ÷ ICC(max) = 91 mW ÷ 7.5 mA = 12.1 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 reli-
able 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.
Continuous-Time Bipolar Switch
A1205
11
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
Package LH, 3-Pin (SOT-23W)
0.55 REF
Gauge Plane
Seating Plane
0.25 BSC
0.95 BSC
0.95
1.00
0.70 2.40
2
1
AActive Area Depth, 0.28 mm REF
B
C
C
B
Reference land pattern layout
All pads a minimum of 0.20 mm from all adjacent pads; adjust as necessary
to meet application process requirements and PCB layout tolerances
Branding scale and appearance at supplier discretion
A
PCB Layout Reference View
Standard Branding Reference View
1
Branded Face
N = Last two digits of device part number
T = Temperature code
NNT
2.90 +0.10
–0.20
4° +4°
–0°
8X 10° REF
0.180+0.020
–0.053
0.05 +0.10
–0.05
0.25 MIN
1.91 +0.19
–0.06
2.98 +0.12
–0.08
1.00 ±0.13
0.40 ±0.10
For Reference Only; not for tooling use (reference dwg. 802840)
Dimensions in millimeters
Dimensions exclusive of mold flash, gate burrs, and dambar protrusions
Exact case and lead configuration at supplier discretion within limits shown
DHall element, not to scale
D
D
D
1.49
0.96
3
Continuous-Time Bipolar Switch
A1205
12
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
Package UA, 3-Pin SIP
Copyright ©2006-2010, Allegro MicroSystems, Inc.
Allegro MicroSystems, Inc. reserves the right to make, from time to time, such de par tures from the detail spec i fi ca tions as may be required to per-
mit improvements in the per for mance, 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’s products are not to be used in life support devices or systems, if a failure of an Allegro product can reasonably be expected to cause the
failure of that life support device or system, or to affect the safety or effectiveness of that device or system.
The in for ma tion in clud ed herein is believed to be ac cu rate and reliable. How ev er, Allegro MicroSystems, Inc. assumes no re spon si bil i ty for its use;
nor for any in fringe ment of patents or other rights of third parties which may result from its use.
For the latest version of this document, visit our website:
www.allegromicro.com
231
0.79 REF
1.27 NOM
2.16
MAX
0.51
REF
45°
C
45°
B
E
E
E
2.04
1.44
Gate burr area
A
B
C
Dambar removal protrusion (6X)
A
D
E
D
Branding scale and appearance at supplier discretion
Hall element, not to scale
Active Area Depth, 0.50 mm REF
For Reference Only; not for tooling use (reference DWG-9049)
Dimensions in millimeters
Dimensions exclusive of mold flash, gate burrs, and dambar protrusions
Exact case and lead configuration at supplier discretion within limits shown
Standard Branding Reference View
= Supplier emblem
N = Last two digits of device part number
T = Temperature code
NNT
1
Mold Ejector
Pin Indent
Branded
Face
4.09 +0.08
–0.05
0.41 +0.03
–0.06
3.02 +0.08
–0.05
0.43 +0.05
–0.07
15.75 ±0.51
1.52 ±0.05
