BU52040HFV

Technical Note

7/12

www.rohm.com

2010.01 - Rev.B

© 2010 ROHM Co., Ltd. All rights reserved.

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Intermittent Operation at Power ON

Fig.17

The Hall Effect IC for wheel keys / trackballs adopts an intermittent operation method in detecting the magnetic field during

startup, as shown in Fig. 17. It outputs to the appropriate terminal based on the detection result and maintains the output

condition during the standby period. The time from power ON until the end of the initial startup period is an indefinite interval,

but it cannot exceed the maximum period, 1200μs. To accommodate the system design, the Hall IC output read should be

programmed within 1200μs of power ON, but after the time allowed for the period ambient temperature and supply voltage.

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Application Example

Wheel Key

Two Hall ICs can enable detection of rotation direction of a magnetic zero-contact wheel key.

Circular magnet

BU52040HFV: 2pcs

Mounting Position of Hall IC Inside Wheel Key

The angular separation of the two Hall ICs within the footprint of the wheel key depends on N/S division angle of the internal

magnet (Φ), and can be set to either Φ/4 or ¾Φ. Mounting the two ICs in this position causes the magnetic phase

difference between the ICs to equal ±1/4, and the direction of rotation can be detected by measuring the change in this

difference. An example of the magnetic field characteristics for this application is shown in the figure below.

S

N

S

N

S

N

S

N

N/S division angle of circular magnet = Φ

Circular Magnet

S N

N

S

Clockwise

rotation

N

S

N S

S

S

S

S

N

N

N

N

Φ

Center of magnet

2) Mounting angle of Hall IC = ¾Φ

Mounting Angle of Hall IC

Hall IC A

θ

Hall IC B

3/4 Φ

Hall IC A

θ

Hall IC B

Center of magnet

Φ/4

1) Mounting angle of Hall IC = Φ/4

Counterclockwise

rotation

Startup time

Standby time

Standby time

Startup time

(Intermittent operation)

Indefinite

OUT

(N magnetic field present)

Indefinite interval

OUT

(S magnetic field present)

Low

High

Supply current

Indefinite interval

(No magnetic field present)

OUT