A1688LUBTN-L-T - ALLEGRO MICROSYSTEMS

The A1688 is a Hall-effect-based integrated circuit (IC) that

provides a user-friendly solution for true zero-speed digital

ring magnet and gear tooth sensing in two-wire applications.

The A1688 is offered in the UB package, which integrates

the IC and a high temperature ceramic capacitor in a single

overmolded SIP package. The integrated capacitor provides

enhanced EMC performance with reduced external components.

The integrated circuit incorporates a dual-element Hall-effect

circuit and signal processing that switches in response to

differential magnetic signals created by magnetic encoders, or,

when properly backbiased with a magnet, from ferromagnetic

targets. The device contains a sophisticated digital circuit that

reduces magnet and system offsets, calibrates the gain for air

gap independent switchpoints, and provides true zero-speed

operation.

Signal optimization occurs at power-up through the combination

of offset and gain-adjust and is maintained throughout operation

with the use of a running-mode calibration scheme. Running-

mode calibration provides immunity from environmental effects

such as micro-oscillations of the sensed target or sudden air

gap changes.

The regulated current output is configured for two-wire interface

circuitry and is ideally suited for obtaining speed information in

wheel speed applications. The Hall element spacing is optimized

for high resolution, small diameter targets. The package is lead

(Pb) free, with 100% matte-tin leadframe plating.

A1688-DS, Rev. 7

MCO-0000633

• Integrated capacitor reduces need for external EMI

protection components

• Wide leads facilitate ease of assembly

• True zero-speed operation

• Automatic Gain Control (AGC) for air gap independent

switchpoints

• Automatic Offset Adjustment (AOA) for signal

processing optimization

• Large operating air gap range

• Internal current regulator for two-wire operation

• Undervoltage lockout

• Single chip sensing IC for high reliability

• On-chip voltage regulator with wide operating voltage

range and stability in the presence of a variety of

complex load impedances

• Fully synchronous digital logic with Scan and IDDQ

testing

Two-Wire, True Zero-Speed, High Accuracy Sensor IC

Package: 2-pin SIP (suffix UB)

Functional Block Diagram

Not to scale

A1688

VCC

GND

Amp AGC

Offset

Adjust

Output

Control

Analog to

Digital

Converter

Digital

Controller

Chopper

Stabilization

Internal Regulator

FEATURES AND BENEFITS DESCRIPTION

March 29, 2019

Two-Wire, True Zero-Speed, High Accuracy Sensor IC

A1688

Allegro MicroSystems, LLC

955 Perimeter Road

Manchester, NH 03103-3353 U.S.A.

www.allegromicro.com

UB Package, 2-Pin SIP Pinout Diagram

ABSOLUTE MAXIMUM RATINGS

Characteristic Symbol Notes Rating Unit

Supply Voltage VCC 28 V

Reverse Supply Voltage VRCC –18 V

Operating Ambient Temperature TAL temperature range –40 to 150 ºC

Maximum Junction Temperature TJ(max) 165 ºC

Storage Temperature Tstg –65 to 170 ºC

Terminal List Table

Name Number Function

VCC 1 Supply Voltage

GND 2 Ground

Internal Discrete Capacitor Ratings

Characteristic Symbol Test Conditions* Value

(Typ.) Unit

Nominal Capacitance CSUPPLY Connected between VCC and GND 2200 pF

SELECTION GUIDE

Part Number Packing* Power-On State

A1688LUBTN–L–T 4000 pieces per 13-in. reel ICC(LOW)

A1688LUBTN–H–T 4000 pieces per 13-in. reel ICC(HIGH)

*Contact Allegro™ for additional packing options.

SPECIFICATIONS

Two-Wire, True Zero-Speed, High Accuracy Sensor IC

A1688

Allegro MicroSystems, LLC

955 Perimeter Road

Manchester, NH 03103-3353 U.S.A.

www.allegromicro.com

Characteristic Symbol Test Conditions Min. Typ.1Max. Unit

ELECTRICAL CHARACTERISTICS

Supply Voltage2VCC Operating, TJ < TJ(max) 4 – 24 V

Undervoltage Lockout VCC(UV) VCC transitioning from 0 → 5 V or 5 → 0 V – 3.6 3.95 V

Reverse Supply Current3IRCC VCC = VRCC(max) – – –10 mA

Supply Zener Clamp Voltage VZSUPPLY ICC = ICC(max) + 3 mA, TA = 25ºC 28 – – V

Supply Zener Current IZSUPPLY TA = 25°C, VCC = 28 V – – 19 mA

OUTPUT

Power-On State POS -H variant – ICC(HIGH) – –

-L variant – ICC(LOW) – –

Supply Current ICC(LOW) Low-current state 5.9 – 8.4 mA

ICC(HIGH) High-current state 12 – 16 mA

Supply Current Ratio ICC(HIGH) /

ICC(LOW)

Measured as ratio of high current to low current

(isothermal) 1.9 – – –

Output Rise Time tr

Corresponds to measured output slew rate with

CSUPPLY; RLOAD = 100 Ω 0 – 1.5 μs

Output Fall Time tf

Corresponds to measured output slew rate with

CSUPPLY; RLOAD = 100 Ω 0 – 1.5 μs

OPERATING CHARACTERISTICS

Operate Point BOP

% of peak-to-peak IC-processed magnetic

signal – 60 – %

Release Point BRP

% of peak-to-peak IC-processed magnetic

signal – 40 – %

Operating Frequency fFWD 0 – 5 kHz

Figure 1: Typical Application Circuit

A1688

VCC

GND

RLOAD

100 Ω CLOAD

Continued on the next page…

OPERATING CHARACTERISTICS: Valid throughout full operating and temperature ranges; unless otherwise specied

Two-Wire, True Zero-Speed, High Accuracy Sensor IC

A1688

Allegro MicroSystems, LLC

955 Perimeter Road

Manchester, NH 03103-3353 U.S.A.

www.allegromicro.com

Characteristic Symbol Test Conditions Min. Typ.1Max. Unit

OPERATING CHARACTERISTICS (continued)

Input Signal BSIG Differential signal, measured peak-to-peak 20 – 1200 G

Allowable User-Induced Differential

Offset BSIGEXT

External differential signal bias (DC), operating

within specification –300 – 300 G

Sensitivity Temperature Coefficient4TC – +0.2 – %/°C

Total Pitch Deviation For constant BSIG, sine wave – – ±2 %

Maximum Sudden Signal Amplitude

Change

BSEQ(n+1)

/ BSEQ(n)

No missed output edge. Instantaneous

symmetric magnetic signal amplitude change,

measured as a percentage of peak-to-peak BSIG

(see figure 2)

– 0.6 – –

Maximum Total Signal Amplitude

Change

BSEQ(max)

/ BSEQ(min)

Overall symmetric magnetic signal amplitude

change, measured as a percentage of peak-to-

peak BSIG

– 0.2 – –

Front-End Chopping Frequency – 400 – kHz

1 Typical values are at TA = 25°C and VCC = 12 V. Performance may vary for individual units, within the specied maximum and minimum limits.

2 Maximum voltage must be adjusted for power dissipation and junction temperature; see representative discussions in Power Derating section.

3 Negative current is dened as conventional current coming out of (sourced from) the specied device terminal.

4 Ring magnets decrease strength with rising temperature. Device compensates. Note that BSIG requirement is not inuenced by this.

BSEQ(n)

BSEQ(n+1)

Figure 2: Di󰀨erential Signal Variation

OPERATING CHARACTERISTICS (continued): Valid throughout full operating and temperature ranges; unless otherwise

specied

Two-Wire, True Zero-Speed, High Accuracy Sensor IC

A1688

Allegro MicroSystems, LLC

955 Perimeter Road

Manchester, NH 03103-3353 U.S.A.

www.allegromicro.com

THERMAL CHARACTERISTICS

Characteristic Symbol Test Conditions* Value Unit

Package Thermal Resistance RθJA Single-layer PCB with copper limited to solder pads 213 ºC/W

*Additional thermal information is available on the Allegro website.

20 40 60 80 100 120 140 160 180

Temperature (ºC)

Maximum Allowable V (V)

VCC(max)

VCC(min)

Power Derating Curve

20 40 60 80 100 120 140 160 180

100

200

300

400

500

600

700

800

900

1000

1100

1200

1300

1400

1500

1600

1700

1800

1900

Temperature (ºC)

Power Dissipation P (mW)

Power Dissipation versus Ambient Temperature

Two-Wire, True Zero-Speed, High Accuracy Sensor IC

A1688

Allegro MicroSystems, LLC

955 Perimeter Road

Manchester, NH 03103-3353 U.S.A.

www.allegromicro.com

FUNCTIONAL DESCRIPTION

Hall Technology

This single-chip differential Hall-effect sensor IC contains two

Hall elements as shown in Figure 5, which simultaneously sense

the magnetic profile of the ring magnet or gear target. The mag-

netic fields are sensed at different points (spaced at a 1.75 mm

pitch), generating a differential internal analog voltage, VPROC ,

that is processed for precise switching of the digital output signal.

The Hall IC is self-calibrating and also possesses a temperature-

compensated amplifier and offset cancellation circuitry. Its

voltage regulator provides supply noise rejection throughout the

operating voltage range. Changes in temperature do not greatly

affect this device due to the stable amplifier design and the offset

rejection circuitry. The Hall transducers and signal processing

electronics are integrated on the same silicon substrate, using a

proprietary BiCMOS process.

Target Profiling During Operation

An operating device is capable of providing digital information

that is representative of the mechanical features of a rotating

gear or ring magnet. The waveform diagram in Figure 5 presents

the automatic translation of the mechanical profile, through the

magnetic profile that it induces, to the digital output signal of

the A1688. No additional optimization is needed and minimal

processing circuitry is required. This ease of use reduces design

time and incremental assembly costs for most applications.

Determining Output Signal Polarity

In Figure 5, the top panel, labeled Mechanical Position, repre-

sents the mechanical features of the ring magnet or gear target

and orientation to the device. The bottom panel, labeled Device

Output Signal, displays the square waveform corresponding

to the digital output signal that results from a rotating target

configured as shown in Figure 4. That direction of rotation (of

the target side adjacent to the package face) is: perpendicular to

the leads, across the face of the device, from the pin 1 side to the

pin 2 side. This results in the device output switching from high

to low output state as a north magnetic pole passes the device

face. In this configuration, the device output voltage switches to

its high polarity when a south pole is the target feature nearest to

the device. If the direction of rotation is reversed or if a part of

type A1688LUBxx-L-x is used, then the output polarity inverts

(see Table 1).

Figure 3: Relative Motion of the Target

Relative Motion of the Target is detected by the dual Hall elements

mounted on the Hall IC.

Figure 4: Target Orientation Relative to Device (ring

magnet shown).

Table 1: Output Polarity when a South Pole Passes

the Package Face in the Indicated Rotation Direction

Rotation Direction Part Type

A1688LUBxx-H-x A1688LUBxx-L-x

Pin 1 → Pin 2 ICC(HIGH) ICC(LOW)

Pin 2 → Pin 1 ICC(LOW) ICC(HIGH)

S N S N

Ring Magnet

Target

Ferromagnetic

Target Tooth Valley

Pin 1

Side

Pin 2

Side

Package Case Branded Face

Hall Element 2 Hall Element 1

Element Pitch

(Top View of

Package Case)

Back-Biasing Magnet

(Externally applied for

ferromagnetic target)

North Pole

South Pole

NSN

SSS

NSN

SSS

Rotation from pin 1 to pin 2

Pin 1 Pin 2

Branded Face

of Package

Rotatin

(Ring magnet or

ferromagnetic)

(Ring magnet or

ferromagnetic)

g Target

Rotation from pin 2 to pin 1

Pin 1 Pin 2

Branded Face

of Package

Rotating Target

Two-Wire, True Zero-Speed, High Accuracy Sensor IC

A1688

Allegro MicroSystems, LLC

955 Perimeter Road

Manchester, NH 03103-3353 U.S.A.

www.allegromicro.com

OP(#1)

OP(#2)

RP(#1)

Device Orientation to Target

IC (Pin 1 Side)

(Pin 2 Side)

Element Pitch

Package Case Branded Face

Target Magnetic Profile

–B

Mechanical Position (Target moves past device pin 1 to pin 2)

Target

(Radial Ring Magnet)

This pole

sensed earlier

This pole

sensed later

(Top View of

Package Case)

Element Pitch

Speed

Channel

E1E2

IC Internal Differential Analog Signals, V

PROC

Device Output Signal,IOUT

OP(#1)

OP(#2)

RP(#1)

IC (Pin 1 Side)

(Pin 2 Side)

Element Pitch

(Top View of

Package Case)

E1E2

Device Orientation to Target

Package Case

Branded Face

External

Back-Biasing Magnet

Speed Channel

Element Pitch

Mechanical Position (Target moves past device pin 1 to pin 2)

Target

(Ferromagnetic)

This tooth

sensed earlier This tooth

sensed later

IC Internal Differential Analog Signals, V

PROC

Target Magnetic Profile

South Pole

North Pole

Device Output Signal,IOUT

Figure 5: Basic Operation

Two-Wire, True Zero-Speed, High Accuracy Sensor IC

A1688

Allegro MicroSystems, LLC

955 Perimeter Road

Manchester, NH 03103-3353 U.S.A.

www.allegromicro.com

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 website.)

The Package Thermal Resistance, RθJA, 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, RθJC, is relatively

small component of RθJA. 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)

 ΔT = PD × RθJA (2)

TJ = TA + ΔT (3)

For example, given common conditions such as: TA= 25°C,

VCC = 12 V, ICC = 14 mA, and RθJA = 213 °C/W, then:

PD = VCC × ICC = 12 V × 14 mA = 168 mW

ΔT = PD × RθJA = 168 mW × 213 °C/W = 38.8°C

TJ = TA + ΔT = 25°C + 38.8°C = 63.8°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 RθJA and TA.

Example: Reliability for VCC at TA

150°C, package UB, using

minimum-K PCB.

Observe the worst-case ratings for the device, specifically:

RθJA

213°C/W, TJ(max) =

165°C, VCC(max)

= 24 V, and

ICC(max) = 16 mA.

Calculate the maximum allowable power level, PD(max). First,

invert equation 3:

ΔTmax = 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) = ΔTmax ÷ RθJA = 15°C ÷ 213 °C/W = 64.9 mW

Finally, invert equation 1 with respect to voltage:

VCC(est) = PD(max) ÷ ICC(max) = 64.9 mW ÷ 16.0 mA = 4.05 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

RθJA. If VCC(est) ≥ VCC(max), then operation between VCC(est) and

VCC(max) is reliable under these conditions.

POWER DERATING

Two-Wire, True Zero-Speed, High Accuracy Sensor IC

A1688

Allegro MicroSystems, LLC

955 Perimeter Road

Manchester, NH 03103-3353 U.S.A.

www.allegromicro.com

Figure 6: Package UB, 2-Pin SIP

Mold Ejector

Pin Indent

0.25 REF

0.30 REF

4 × 2.50 REF

4 × 7.37 REF

4 × 0.85 REF

0.38 REF

0.25 REF

45°

4 × 10°

Branded

Face

0.25 +0.05

–0.03

0.42 ±0.10

1.00 ±0.10

2.54 REF

12.20 ±0.1

DBranding scale and appearance at supplier discretion

1.125

E2 E

1.75

1.45 E

For Reference Only–Not for Tooling Use

(Reference DWG-9070)

Dimensions in millimeters

Dimensions exclusive of mold ﬂash, gate burrs, and dambar protrusions

Exact case and lead conﬁguration at supplier discretion within limits shown

Dambar removal protrusion (8×)

Gate and tie bar burr area

Active Area Depth, 0.38 mm REF

Hall elements (E1 and E2); not to scale

Molded Lead Bar for preventing damage to leads during shipment

0.85 ±0.07

4.00

1.80

±0.10

1.50 ±0.05

4.00 +0.06

–0.05

+0.06

–0.07

1.80+0.06

–0.07

+0.06

–0.05

= Supplier emblem

= Last three digits of device part number

= Last 2 digits of year of manufacture

= Week of manufacture

= Lot number

Standard Branding Reference View

YYWW

LLLL

NNN

PACKAGE OUTLINE DRAWING

Two-Wire, True Zero-Speed, High Accuracy Sensor IC

A1688

Allegro MicroSystems, LLC

955 Perimeter Road

Manchester, NH 03103-3353 U.S.A.

www.allegromicro.com

Revision History

Number Date Description

– March 18, 2014 Initial release. No change from Preliminary Rev. 2.6

1 October 1, 2014 Revised Package Outline Drawing and reformatted datasheet

2 November 10, 2014 Deleted redundant Thermal Characteristics table from page 2

3 December 15, 2014 Corrected error on Package Outline Drawing

4 March 24, 2015 Updated branding on Package Outline Drawing

5 July 10, 2015 Removed bulk options from Selection Guide on page 2

6 March 1, 2016 Updated Internal Discrete Capacitor Ratings table and Package Outline Drawing

7 March 29, 2019 Minor editorial updates

For the latest version of this document, visit our website:

www.allegromicro.com

Allegro MicroSystems, LLC 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’s products are not to be used in any devices or systems, including but not limited to life support devices or systems, in which a failure of

Allegro’s product can reasonably be expected to cause bodily harm.

The information included herein is believed to be accurate and reliable. However, Allegro MicroSystems, LLC assumes no responsibility for its

use; nor for any infringement of patents or other rights of third parties which may result from its use.

Copies of this document are considered uncontrolled documents.