Technical Note

BU52002GUL,BU52003GUL,BU52012HFV,BU52013HFV

10/13

www.rohm.com

2010.01 - Rev.B

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

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Intermittent Operation at Power ON

The unipolar detection Hall IC adopts an intermittent operation method in detecting the magnetic field during startup, as

shown in Fig. 37. 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, 100ms. To accommodate the system design, the Hall IC output read should be

programmed within 100ms of power ON, but after the time allowed for the period ambient temperature and supply voltage.

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Magnet Selection

Of the two representative varieties of permanent magnet, neodymium generally offers greater magnetic power per volume

than ferrite, thereby enabling the highest degree of miniaturization, Thus, neodymium is best suited for small equipment

applications. Fig. 38 shows the relation between the size (volume) of a neodymium magnet and magnetic flux density. The

graph plots the correlation between the distance (L) from three versions of a 4mm X 4mm cross-section neodymium magnet

(1mm, 2mm, and 3mm thick) and magnetic flux density. Fig. 39 shows Hall IC detection distance – a good guide for

determining the proper size and detection distance of the magnet. Based on the BU52012HFV,BU52013HFV operating point

max 5.0 mT, the minimum detection distance for the 1mm, 2mm and 3mm magnets would be 7.6mm, 9.22mm, and 10.4mm,

respectively. To increase the magnet’s detection distance, either increase its thickness or sectional area.

Power ON

Startup time

Standby time

Standby time

Startup time

(Intermittentaction)

Indefinite

OUT

(No magnetic

field present)

Indefinite

OUT

(Magnetic

field present)

Low

High

Supply current

Fig.37

0

1

2

3

4

5

6

7

8

9

10

02

46

8

10

12

14

16

18

20

Distance between magnet and Hall IC [mm]

Fig.38

7.6mm

t=3mm

t=1mm

t=2mm

9.2mm 10.4mm

Magnet material: NEOMAX-44H (material)

Maker: NEOMAX CO.,LTD.

X=Y=4mm

t=1mm,2mm,3mm

X

t

Y

…Flux density measuring point

L: Variable

t

Fig.39 Magnet Dimensions and Flux Density Measuring Point

Magnet size

Magnet