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參數資料
| 型號： | AD7862BR-3 |
| 廠商： | ANALOG DEVICES INC |
| 元件分類： | ADC |
| 英文描述： | Simultaneous Sampling Dual 250 kSPS 12-Bit ADC |
| 中文描述： | 2-CH 12-BIT SUCCESSIVE APPROXIMATION ADC, PARALLEL ACCESS, PDSO28 |
| 封裝： | SOIC-28 |
| 文件頁數： | 14/16頁 |
| 文件大小： | 414K |
| 代理商： | AD7862BR-3 |
AD7862
–14–
REV. 0
Some applications may require that the conversion be initiated
by the microprocessor rather than an external timer. One option
is to decode the AD7862
CONVST
from the address bus so
that a write operation starts a conversion. Data is read at the
end of the conversion sequence as before. Figure 18 shows an
example of initiating conversion using this method. Note that
for all interfaces, it is preferred that a read operation not be
attempted during conversion.
AD7862–MC68000 Interface
An interface between the AD7862 and the MC68000 is shown
in Figure 17. As before, conversion can be supplied from the
MC68000 or from an external source. The AD7862 BUSY line
can be used to interrupt the processor or, alternatively, software
delays can ensure that conversion has been completed before a
read to the AD7862 is attempted. Because of the nature of its
interrupts, the 68000 requires additional logic (not shown in
Figure 18) to allow it to be interrupted correctly. For further
information on 68000 interrupts, consult the 68000 user’s manual.
The MC68000
AS
and R/
W
outputs are used to generate a
separate
RD
input signal for the AD7862.
CS
is used to drive
the 68000 DTACK input to allow the processor to execute a
normal read operation to the AD7862. The conversion results
are read using the following 68000 instruction:
MOVE.W ADC,D0
where
D0
is the 68000 D0 register, and
ADC
is the AD7862
address.
A0
A15
D15
D0
EN
ADDR
DECODE
ADDRESS BUS
OPTIONAL
DATA BUS
CONVST
CS
DB11
DB0
RD
AD7862*
MC68000
*ADDITIONAL PINS OMITTED FOR CLARITY
DTACK
R/W
AS
A0
Figure 17. AD7862–MC68000 Interface
AD7862–80C196 Interface
Figure 18 shows an interface between the AD7862 and the
80C196 microprocessor. Here, the microprocessor initiates
conversion. This is achieved by gating the 80C196
WR
signal
with a decoded address output (different to the AD7862
CS
address). The AD7862 BUSY line is used to interrupt the
microprocessor when the conversion sequence is completed.
D15
D0
ADDR
DECODE
ADDRESS BUS
ADDRESS/DATA BUS
CONVST
CS
DB11
DB0
RD
AD7862*
80C196
*ADDITIONAL PINS OMITTED FOR CLARITY
WR
RD
A0
A15
A1
Figure 18. AD7862–8086 Interface
Vector Motor Control
The current drawn by a motor can be split into two compo-
nents: one produces torque, and the other produces magnetic
flux. For optimal performance of the motor, these two compo-
nents should be controlled independently. In conventional
methods of controlling a three-phase motor, the current (or
voltage) supplied to the motor and the frequency of the drive are
the basic control variables; however, both the torque and flux
are functions of current (or voltage) and frequency. This
coupling effect can reduce the performance of the motor
because, if the torque is increased by increasing the frequency,
for example, the flux tends to decrease.
Vector control of an ac motor involves controlling phase in
addition to drive and current frequency. Controlling the phase
of the motor requires feedback information on the position of
the rotor relative to the rotating magnetic field in the motor.
Using this information, a vector controller mathematically
transforms the three phase drive currents into separate torque
and flux components. The AD7862, with its four-channel
simultaneous sampling capability, is ideally suited for use in
vector motor control applications.
A block diagram of a vector motor control application using the
AD7862 is shown in Figure 19. The position of the field is
derived by determining the current in each phase of the motor.
Only two phase currents need to be measured because the third
can be calculated if two phases are known. V
A1
and V
A2
of the
AD7862 are used to digitize this information.
Simultaneous sampling is critical to maintain the relative phase
information between the two channels. A current sensing
isolation amplifier, transformer or Hall effect sensor is used
between the motor and the AD7862. Rotor information is
obtained by measuring the voltage from two of the inputs to the
motor. V
B1
and V
B2
of the AD7862 are used to obtain this
information. Once again, the relative phase of the two channels
is important. A DSP microprocessor is used to perform the
mathematical transformations and control loop calculations on
the information fed back by the AD7862.
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