Circuit description

L6229Q

16/28

Doc ID 15209 Rev 3

5.4

Slow decay mode

Figure 13 shows the operation of the bridge in the slow decay mode during the off time. At

any time only two legs of the three-phase bridge are active, therefore only the two active

legs of the bridge are shown in the figure and the third leg will be off. At the start of the Off

Time, the lower power MOS is switched off and the current recirculates around the upper

half of the bridge. Since the voltage across the coil is low, the current decays slowly. After

the dead time the upper power MOS is operated in the synchronous rectification mode

reducing the impedance of the freewheeling diode and the related conducting losses. When

the monostable times out, upper MOS that was operating the synchronous mode turns off

and the lower power MOS is turned on again after some delay set by the dead time to

prevent cross conduction.

Figure 13.

Slow decay mode output stage configurations

5.5

Decoding logic

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

three-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 the

configuration 6a is the same than 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

A) ON TIME

B) 1

μs DEAD TIME

C) SYNCHRONOUS

RECTIFICATION

D) 1

μs DEAD TIME

D01IN1336