AN1857 Freescale Semiconductor / Motorola, AN1857 Datasheet - Page 17

• Manufacturer Part Number: AN1857
• Description: A 3-Phase ac Induction Motor Control System Based on the MC68HC908MR32
• Manufacturer: Freescale Semiconductor / Motorola

Optoisolation
Board
Digital
Optoisolation
Circuit
AN1857
MOTOROLA
DIGITAL SIGNAL IN
GND_CB
MC74HCT00AD
10 k
R1
The optoisolation board has a number of individual circuit blocks. The
first circuit is a power supply block, supplying +5 Vdc, +3.3 Vdc,
+15 Vdc, and –15 Vdc to the board. The power circuits are comprised of
individual linear regulators. The next circuit is a digital optoisolation
circuit. The last circuit is a linear optoisolation circuit. A discussion of the
optoisolation blocks follows.
Figure 9
digital optoisolation circuit used on the optoisolation board. The circuits
are used to couple several control signals from the control board to the
power board. Those signals are the six PWM signals, one spare
bidirectional optoisolation I/O, one PFC inhibit, one PFC PWM, and one
motor brake control signal from the controller board to the power stage.
Also, the optoisolation board is used to couple four digital feedback
signals from the power board to the control board. Those signals are
phases A, B, and C zero cross signals and a PFC zero cross signal.
The digital isolation block is based on Agilent Technologies’ HCPL-J454
high dv/dt coupler. A simplified schematic is shown in
the MR32 is reset, and until its I/O has been set up by the system
software, in most cases, its outputs are three-stated. R1 sets a logic low
in the absence of a signal. Open input pull down is important for gate
drive signals, where it is desirable to keep power transistors off in case
of either a broken connection or absence of power on the control board
or until the I/O ports have been set up.
2
1
U1A
+5V_D_CB
Freescale Semiconductor, Inc.
Figure 9. Digital Optoisolation Circuit
For More Information On This Product,
14
7
GND_CB
3
is a simplified schematic diagram of the basic design of the
330
R2
Go to: www.freescale.com
+5V_D_CB
2
ANODE
CATHODE
3
D1
HCPL-J454#300
ISO1
Q1
D2
8
6
5
GND
V
V
Out
CC
+5V_D_PS
GND_PS
1.8 k
R3
MC74HCT14AD
3
U2A
4
Figure
System Hardware
DIGITAL SIGNAL OUT
Application Note
9. When
17