A3211 and A3212: Micropower, Ultrasensitive Hall-Effect Switches

The A3211 and A3212 integrated circuits are ultrasensitive, pole independent Hall-effect switches with latched digital output. These devices are especially suited for operation in battery-operated, hand-held equipment such as cellular and cordless telephones, pagers, and palmtop computers. A 2.5 to 3.5 V operation and a unique clocking scheme reduce the average operating power requirements to less than 15 µW with a 2.75 V supply.

Unlike other Hall-effect switches, either a north or south pole of sufficient strength will turn the output on in the A3212, and in the absence of a magnetic field, the output is off. The A3211 provides an inverted output. The polarity independence and minimal power requirements allow these devices to replace reed switches for superior reliability and ease of manufacturing, while eliminating the requirement for signal conditioning.

Improved stability is made possible through chopper stabilization (dynamic offset cancellation), which reduces the residual offset voltage normally caused by device overmolding, temperature dependencies, and thermal stress.

This device includes on a single silicon chip a Hall-voltage generator, small-signal amplifier, chopper stabilization, a latch, and a MOSFET output. Advanced CMOS processing is used to take advantage of low-voltage and low-power requirements, component matching, very low input-offset errors, and small component geometries.

Four package styles provide magnetically optimized solutions for most applications. Miniature low-profile surface-mount package types EH and EL (0.75 and 0.50 mm nominal height) are leadless, LH is a 3-pin low-profile SMD, and UA is a three-pin SIP for through-hole mounting. Packages are lead (Pb) free (suffix, –T) with 100% matte tin plated leadframes.

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  • Features and BenefitsFeatures and Benefits
  • PackagingPackaging
  • Technical DocsTechnical Docs
  • NewsNews
  • AEC-Q100 automotive qualified 
  • Micropower operation
  • Operate with north or south pole
  • 2.5 to 3.5 V battery operation
  • Chopper stabilized
    • Superior temperature stability
    • Extremely low switch-point drift
    • Insensitive to physical stress
  • Solid-state reliability
  • Small size
  • Simply manufacturable with magnet pole independence

Four package styles provide magnetically optimized solutions for most applications.

Miniature low-profile surface-mount package types EH and EL (0.75 and 0.50 mm nominal height) are leadless, LH is a 3-pin low-profile SMD, and UA is a three-pin SIP for through-hole mounting. Packages are lead (Pb) free (suffix, –T) with 100% matte tin plated leadframes.

Packages

Application Notes

Frequently-Asked Questions

1. Is the A3212 "pole independent"?

Yes. This device is different from Allegro's other unipolar switches because it is pole independent. The term "pole independent" refers to the unique feature of being able to switch on with either a north- or south-pole magnet of sufficient strength. Omnipolar switch is the term for a unipolar switch with pole independence.

2. What is the supply voltage range of the A3212?

The supply range is 2.5 V to 3.5 V.

3. Why is the supply range so much lower and tighter than other Allegro Hall sensor ICs?

Unlike other Allegro Hall sensor ICs, the A3212 does not have its own internal voltage regulator. The regulator was intentionally left out in order to conserve power. The target applications in which it is designed into are battery powered such as cell phones, PDAs, etc. Therefore, the regulator is not as important and can be removed to conserve power on current.

4. Does the A3212 require any external circuitry?

It is strongly recommended that an external bypass capacitor be connected (in close proximity to the Hall sensor IC) between the supply and ground pins of the device to reduce both external noise and noise generated by the chopper-stabilization technique. Additional circuitry may also be required if there are any transients on the line or if reverse battery is possible in the application. The absolute maximum voltage for this part is 5 V and there is no reverse battery protection.

5. What package styles is this device offered in?

The A3212 is available in either the '-UA' (3-lead ultra-mini SIP) through-hole package or the SOT-23 type '-LH' (miniature low profile) surface-mount package.

6. What is the operating temperature range?

The A3212 standard operating range 'E' is from -40°C to +85°C. This device is also available in an extended temperature range 'L' version (-40°C to 150°C).

7. On power up, when will this device begin sampling?

After 90 ms.

8. Can the A3212 be used to detect a moving object such as a rotating magnet?

Yes, but the period of the magnet's rotation must be at least 90 ms. If it is not, there is a chance that this sensor could miss "seeing" the magnet during the sleep mode of its operation.

9. What are the differences between the A3212 and A3210?

The A3212 is an improvement to the A3210 in power consumption, magnetic switch points, and offers an extended temperature range as referenced in question 6. The max supply current of the 3212 is lower at 10 µA at 2.75 V, versus the 3210 which is 25 µA. The switch points are tighter with a BOP of ±55 Gauss and BRP of ±10 Gauss compared to the A3210 with a BOP of ±60 Gauss and BRP of ±5 Gauss. The switch point change allows for operation with a weaker magnetic field while compensating for magnetic noise created by such things as a cellular phone speaker or computer hard drive. The changes make the new device more attractive to applications concerned with battery life and switch point sensitivity.

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Part Number Specifications and Availability

Part Number Package Type Temperature RoHS
Compliant
Part Composition /
RoHS Data
Comments Samples Check
Distributor Stock
A3211EEHLT-T 6-lead MLP -40°C to 85°C Yes View Data Discontinued Contact your
local sales rep
Check Stock
A3211EELLT-T 3-lead MLP -40°C to 85°C Yes View Data Last time buy Contact your
local sales rep
Check Stock
A3211ELHLT-T 3-lead SOT -40°C to 85°C Yes View Data Contact your
local sales rep
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A3211ELHLX-T 3-lead SOT -40°C to 85°C Yes View Data Contact your
local sales rep
Check Stock
A3212EEHLX-T 6-lead MLP -40°C to 85°C Yes View Data Discontinued Contact your
local sales rep
Check Stock
A3212EELLT-T 3-lead MLP -40°C to 85°C Yes View Data Last time buy Contact your
local sales rep
Check Stock
A3212ELHLT-T 3-lead SOT -40°C to 85°C Yes View Data Contact your
local sales rep
Check Stock
A3212ELHLX-T 3-lead SOT -40°C to 85°C Yes View Data Contact your
local sales rep
Check Stock
A3212EUA-T 3-lead SIP -40°C to 85°C Yes View Data Contact your
local sales rep
Check Stock
A3212LLHLT-T 3-lead SOT -40°C to 150°C Yes View Data Contact your
local sales rep
Check Stock
A3212LLHLX-T 3-lead SOT -40°C to 150°C Yes View Data Contact your
local sales rep
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A3212LUA-T 3-lead SIP -40°C to 150°C Yes View Data Contact your
local sales rep
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