AD7864ASZ-2 Analog Devices Inc, AD7864ASZ-2 Datasheet - Page 25

• Manufacturer Part Number: AD7864ASZ-2
• Description: IC ADC 14BIT DUAL 4CHAN 44-MQFP
• Manufacturer: Analog Devices Inc

Specifications of AD7864ASZ-2

• Data Interface: Parallel
• Number Of Bits: 12
• Sampling Rate (per Second): 520k
• Number Of Converters: 1
• Power Dissipation (max): 120mW
• Voltage Supply Source: Analog and Digital
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 44-MQFP, 44-PQFP
• Resolution (bits): 12bit
• Sampling Rate: 500kSPS
• Input Channel Type: Single Ended
• Supply Voltage Range - Analog: 4.75V To 5.25V
• Supply Current: 24mA
• Digital Ic Case Style: QFP
• Number Of Elements: 1
• Resolution: 12Bit
• Architecture: SAR
• Sample Rate: 520KSPS
• Input Polarity: Unipolar
• Input Type: Voltage
• Rated Input Volt: 2.5/5V
• Differential Input: No
• Power Supply Requirement: Analog and Digital
• Single Supply Voltage (typ): 5V
• Single Supply Voltage (min): 4.75V
• Single Supply Voltage (max): 5.25V
• Dual Supply Voltage (typ): Not RequiredV
• Dual Supply Voltage (min): Not RequiredV
• Dual Supply Voltage (max): Not RequiredV
• Power Dissipation: 120mW
• Differential Linearity Error: ±0.9LSB
• Integral Nonlinearity Error: ±1LSB
• Operating Temp Range: -40C to 85C
• Operating Temperature Classification: Industrial
• Mounting: Surface Mount
• Pin Count: 44
• Package Type: MQFP
• Input Signal Type: Single-Ended
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant, Lead free / RoHS Compliant

VECTOR MOTOR CONTROL
The current drawn by a motor can be split into two components:
one produces torque and the other produces magnetic flux. For
optimal performance of the motor, control these two compo-
nents 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, for example, if
the torque is increased by increasing the frequency, the flux
tends to decrease.
V
V
V
V
IN1
IN2
IN3
IN4
DB0 TO DB11
AD7864
CONVST
Figure 25. AD7864 to MC68HC000 Interface
CS
RD
ADDRESS
DECODE
CLOCK
SETPOINT
SETPOINT
TORQUE
*ADDITIONAL PINS OMITTED FOR CLARITY.
FLUX
DTACK
AS
R/W
D0 TO D15
A0 TO A15
DSP MICROPROCESSOR
PHASE INFORMATION
CALCULATIONS AND
TORQUE AND FLUX
MC68HC000
TRANSFORMATION
+
TO TORQUE AND
CONTROL LOOP
TWO TO THREE
FLUX CURRENT
Figure 26. Vector Motor Control Using the AD7864
COMPONENTS
–
+
–
Rev. D | Page 25 of 28
DAC
DAC
DAC
AD7864*
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 trans-
forms the three-phase drive currents into separate torque and
flux components. The AD7864, with its 4-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
AD7864 is shown in Figure 26. 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
AD7864 are used to digitize this information.
Simultaneous sampling is critical to maintain the relative phase
information between the two channels. A current sensing isola-
tion amplifier, transformer, or Hall effect sensor is used between
the motor and the AD7864. Rotor information is obtained by
measuring the voltage from two of the inputs to the motor. V
and V
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 AD7864.
V
V
V
V
IN1
IN2
IN3
IN4
CIRCUITRY
IN4
DRIVE
AMPLIFIERS
ISOLATION
ATTENUATORS
of the AD7864 are used to obtain this information.
VOLTAGE
I
I
I
C
B
A
V
V
B
A
THREE-
PHASE
MOTOR
IN1
and V
IN2
AD7864
of the
IN3