PRELIMINARY
ML4435
FUNCTIONAL DESCRIPTION
mutation to achieve rotational motion. Electronic com-
mutation requires the switching on and off of the power
switches of a 3 phase half bridge. For torque production
to be achieved in one direction the commutation is dic-
tated by the rotor’s position. Electronic commutation in
the ML4435 is achieved by turning on and off, in the
proper sequence, one L output from one phase and one H
output from another phase. There are six combinations of
L and H outputs (six switching states) that constitute a full
commutation cycle as illustrated in Table 1 labeled state
A through F. This switching sequence is programmed into
the commutation state machine as illustrated in Figure 6.
Clocking of the commutation state machine is provided by
the output of a VCO.
(pin 2) proportional to the input voltage to the voltage
controlled oscillator SPEED FB (pin 18). The proportion of
frequency to voltage or VCO constant Kv is set by a resistor
to ground on RVCO (pin 4) and capacitor to ground on
CVCO (pin 20) as shown in Figure 7. RVCO sets up a
current proportional to the VCO input voltage SPEED FB
minus 0.7V. This current is used to charge and discharge
CVCO between the threshold voltages of 2V and 3.75V as
shown in Figure 7. RVCO has a lower voltage limit of 0.2V.
The resulting triangle wave of CVCO corresponds to the
clock on the TACH pin, this is also illustrated in Figure 7. Kv
should be set so that the VCO output frequency corresponds
to the maximum commutation frequency FMAX and thus the
maximum motor speed when the VCO input is equal to or
slightly less than 6V. CVCO and RVCO can be selected by
first calculating FMAX and then using the selection graph in
Figure 8. FMAX is calculated as follows:
VOLTAGE CONTROLLED OSCILLATOR
The VCO outputs a TTL compatible clock on the TACH
FMAX = 0.05 x RPMMAX x N
OUTPUT DRIVERS
Where: RPMMAX = The maximum speed of operation
(RPM). N = The number of magnetic poles (Unitless).
LA
LB
LC
HA
HB
HC
TACH
A
B
C
LOW LOW HI
H
LOW HI H HI
H
H
H
The TACH (pin 2) outputs the VCO frequency. This is 6
LOW LOW HI H HI
H
H
LOW HI
LOW HI
HI
HI
H
H
LOW LOW HI
D
E
LOW LOW HI H HI
H
H
LOW
LOW
LOW HI
LOW HI
H
H
LOW HI H HI
SPEED FB
F
LOW LOW HI H HI
H
-
LEVEL
SHIFT
0. V
+
= DRIVER ON
CVCO
3. 5V
Table 1. Communication Control States
20
2V
VOLTA E
CONTROLLED
OSCILLATOR
RVCO
4
COMMUTATION
STATE MACHINE
R
0.9V
CLK VCO
3 s
A
POWER ON
RESET PULSE
F
E
B
C
D
Figure 6. Commutation State Machine
Figure 7. VCO Control
May, 2000
PRELIMINARY DATASHEET
7
MICRO-LINEAR [ MICRO LINEAR CORPORATION ]
