LM621N NSC [National Semiconductor], LM621N Datasheet - Page 10

• Manufacturer Part Number: LM621N
• Description: LM621 Brushless Motor Commutator
• Manufacturer: NSC [National Semiconductor]

Figure 6 is typical of the circuitry used to commutate a four-
Typical Applications
FOUR-PHASE EXAMPLE
phase motor using the LM621 This application is seen to
differ from the three-phase application example in that the
LM621 outputs are utilized differently Four-phase motors
require four-phase power switches which in turn require the
commutator to provide four current-sinking outputs and four
current sourcing outputs The 18-pin package of the LM621
facilitates only three sinking and three sourcing outputs The
schematic shows the 30 60 SELECT input in the 30-degree
select state (pin 8 high) and rotor-position sensor inputs
HS2 and HS3 connected together This connection trun-
cates the number of possible rotor-position input states to
four which is consistent with the 90-degree quadrature ro-
tor-position signals provided by four-phase motors With the
LM621 outputs connected as shown this approach pro-
vides the needed power-switch drive signals for a four-
phase motor Note that only four of the six LM621 outputs
(Continued)
FIGURE 6 Commutation of Four-Phase Motor
10
(SINK
directly and that these are also inverted to form the remain-
ing four SINK
HALF-WAVE DRIVE EXAMPLE
The previous applications examples involved delta-config-
ured motor windings and full-wave operation of the motor
The application shown in Figure 7 differs in that it features
half-wave operation of a motor with the windings in a Y-con-
figuration This approach is suitable for automotive and oth-
er applications where only low-voltage power supplies are
conveniently available The advantage of this power-switch-
ing scheme is that there is only one switch-voltage drop in
series with the motor winding thereby conserving more of
the available voltage for application to the motor winding
Half-wave operation provides only unidirectional current to
the windings in contrast to the bidirectional currents applied
by the previous full-wave examples
1 and
2 and SOURCE
3 and SOURCE
2 outputs are not used
1 and
3) are used
TL H 8679 – 11