2 x 4 -Ch a n n e l, S im u lt a n e o u s -S a m p lin g
1 4 -Bit DAS
V
CC
V
CC
HC161
1/2 HC74
Q
PRE
D
CLR
ENP
RD
P = Q
G
Q
ENT
LOAD
HC688
CLR
V
(LSB) 0
1
CC
A
B
C
P0
P1
P2
P3
2
3
INT
D
RCO
P4
P5
P6
P7
5/MAX126
EXTERNAL
CLOCK
V
CC
Q0
Q1
Q2
Q3
LATCH
CLOCK
(TO 16373 LATCH)
10k
Q4
Q5
Q6
Q7
CH1
0
1
0
1
0
0
1
1
EXTERNAL
CLOCK
CH2
CH3
CH4
Figure 9. Output Demultiplexer Circuit
The circuit of Figure 10 shows a typical vector motor-
control application using all available inputs of the
MAX125/MAX126. CH1A and CH2A are connected
to two isolated Hall-effect current sensors and are a
part of the current (torque) feedback loop. The
MAX125/MAX126 digitize the currents and deliver raw
data to the following DSP and controller stages, where
the vector processing takes place. Sensorless vector
control uses a computer model for the motor and an
algorithm to split each output current into its magnetiz-
ing (stator current) and torque-producing (rotor current)
components.
If a 2- to 3-phase conversion is not practical, three cur-
rents can be sampled simultaneously with the addition
of a third sensor (not shown). Optional voltage
(position) feedback can be derived by measuring two
phase voltages (CH3A, CH4A). Typically, an isolated
differential amplifier is used between the motor and the
MAX125/MAX126. Again, the third phase voltage can
be derived from the magnitude (phase voltage) and its
relative phase.
For optimum speed control and good load regulation
close to zero speed, additional velocity and position
feedback are derived from an encoder or resolver and
12 ______________________________________________________________________________________
MAXIM [ MAXIM INTEGRATED PRODUCTS ]
