Decoding logic

L6235

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DocID7618 Rev 2

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Decoding logic

The decoding logic section is a combinatory logic that provides the appropriate driving of the

3-phase bridge outputs according to the signals coming from the three hall sensors that

detect rotor position in a 3-phase BLDC motor. This novel combinatory logic discriminates

between the actual sensor positions for sensors spaced at 60, 120, 240 and 300 electrical

degrees. This decoding method allows the implementation of a universal IC without

dedicating pins to select the sensor configuration.

There are eight possible input combinations for three sensor inputs. Six combinations are

valid for rotor positions with 120 electrical degrees sensor phasing (see Figure 14, positions

1, 2, 3a, 4, 5 and 6a) and six combinations are valid for rotor positions with 60 electrical

degrees phasing (see Figure 15, positions 1, 2, 3b, 4, 5 and 6b). Four of them are in

common (1, 2, 4 and 5) whereas there are two combinations used only in 120 electrical

degrees sensor phasing (3a and 6a) and two combinations used only in 60 electrical

degrees sensor phasing (3b and 6b).

The decoder can drive motors with different sensor configuration simply by following

output configuration 6a is the same as 6b.

The sequence of the hall codes for 300 electrical degrees phasing is the reverse of 60 and

the sequence of the hall codes for 240 phasing is the reverse of 120. So, by decoding the 60

and the 120 codes it is possible to drive the motor with all the four conventions by changing

the direction set.

Table 7. 60 and 120 electrical degree decoding logic in forward direction

Hall 120°

1

2

3a

-

4

5

6a

-

Hall 60°

1

2

-

3b

4

5

-

6b

HH

L

H

L

L

H

L

LH

H

H

H

L

L

L

LL

L

H

H

H

H

L

Vs

High Z

GND

GND

GND

High Z

Vs

Vs

High Z

Vs

Vs

Vs

High Z

GND

GND

GND

GND

GND

High Z

High Z

Vs

Vs

High Z

High Z

Phasing

1 -> 3

2 -> 3

2 -> 1

2 -> 1

3 -> 1

3 -> 2

1 -> 2

1 -> 2