MAX115/MAX116
2x4-Channel, Simultaneous-Sampling
12-Bit ADCs
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part of the current (torque) feedback loop. The
MAX115/MAX116 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 two-to-three phase conversion is not practical,
three currents 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
MAX115/MAX116. 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
brought to the MAX115/MAX116 at CH4B. The addi-
tional channels can be used to evaluate slower analog
inputs, such as the main DC bus voltage (CH2B), tem-
perature sensors (CH3B), or other analog inputs (AUX,
CH1B).
Power-Supply Bypassing
and Ground Management
For optimum system performance, use printed circuit
boards with separate analog and digital ground planes.
Wire-wrapped boards are not recommended. Connect
the two ground planes together at the low-impedance
power-supply source. For the best ground connection,
connect the DGND and AGND pins together and con-
nect that point to the system analog ground plane to
avoid interference from other digital noise sources. If
DGND is connected to the system digital ground, digi-
tal noise may get through to the ADC’s analog portion.
The AGND pins must be connected directly to a low-
impedance ground plane. Extra impedance between
the pins and the ground plane increases crosstalk and
degrades INL.
