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A1185EUA

Ultrasensitive Two-Wire Field-Programmable Chopper-Stabilized Unipolar Hall-Effect Switches

Allegro MicroSystems 

A1185 and

A1186

Ultrasensitive Two-Wire Field-Programmable

Chopper-Stabilized Unipolar Hall Effect Switches

Application Information

For additional general application information, visit the Allegro

Web site at www. allegromicro.com.

Typical Application and Programming Circuit

The A118x family of devices MUST be protected by an exter-

nal bypass capacitor, CBYP, connected between the supply pin,

VCC, and the ground pin, GND, of the device. CBYP reduces

both external noise and the noise generated by the chopper-sta-

bilization function. As shown in figure 3, a 0.01 μF capacitor

is typical. (For programming the device, a 0.1 μF capacitor is

recommended for proper fuse blowing.)

Installation of CBYP must ensure that the traces that connect

it to the A118x pins are no greater than 5 mm in length. (For

programming the device, the capacitor may be further away from

the device, including mounting on the board used for program-

ming the device.)

CBYP serves only to protect the A118x internal circuitry. All

high-frequency interferences conducted along the supply lines

are passed directly to the load through CBYP. As a result, the

load ECU (electronic control unit) must have sufficient protec-

tion, other than CBYP, installed in parallel with the A118x.

A series resistor on the supply side, RS (not shown), in combina-

tion with CBYP, creates a filter for EMI pulses.

When determining the minimum VCC requirement of the A118x

device, the voltage drops across RS and the ECU sense resistor,

RSENSE, must be taken into consideration. The typical value for

RSENSE is approximately 100 Ω. (All programming, including

code and lock-bit programming, should be done with direct

connections to VCC and GND, with the use of a 0.1uF bypass

capacitor. Programming across the series resistor or sense resis-

tor may not allow enough energy to properly blow the fuses

in the device, as required for proper programming. The result

would be incorrect switchpoints.

V+

VCC

B

A118x

GND

A

GND

RSENSE

CBYP

0.01 uF

B

A Package UA Only

B Maximum separation 5 mm

ECU

Figure 3. Typical application circuit

Allegro MicroSystems, Inc.

8

115 Northeast Cutoff, Box 15036

Worcester, Massachusetts 01615-0036 (508) 853-5000

www.allegromicro.com

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