DM330023-2 datasheet(44/64 Pages) MICROCHIP

44 / 64 page

dsPICDEM™ MCHV Development System User’s Guide

DS70605A-page 38

 2009 Microchip Technology Inc.

4.2.4

Feedback Circuitry

The Power Module Stage provides three different methods to sense the motor position.

These signals are also useful to determine the speed, the torque, current consumption

and the applied voltage.

Hall Sensors, the hall sensors circuitry is designed to attach open-collector configured

sensors. It has a pull-up resistor at the hall sensor inputs (R23, R24, and R25) and a

voltage divider (R26-R29, R27-R30, R28-R31) in order to scale the input waveforms to

the dsPIC DSC logic levels. C25-C27 and R26-R28 form a low-pass RC filter for each

hall sensor signal.

Phase Voltage Feedback circuitry for each phase is compounded by a voltage divider,

a current limiter and a low-pass RC filter. R79, R84 and R92 scale the phase M1 volt-

age in order to match the dsPIC DSC logic levels. R85 limits the current going to the

ADC pin (< 6mA). C51, R79 and R84 form the low-pass filter. The phase M2 and M3

has the exact same circuitry as shown in the schematic.

DC Bus Voltage Feedback is compounded by a voltage divider and a low-pass RC

filter. R75, R76 and R81 scale the DC bus voltage in order to match the dsPIC DSC

logic levels. C47, R75 and R76 form the low-pass filter.

Inverter Leg Shunt Resistor Feedback, a shunt resistor is located between the emit-

ter of the low side switches M1 and M2 and the “-DC bus”. A simple differential amplifier

circuit is used as shown in Appendix A. The operation of the circuit used for the M1

phase leg is described below:

The current is measured using the shunt resistor R86 and the operational amplifier

MCP6024 (U13A); R32, R33, R34, R36, R37 and R38 set the gain. R38 shifts the volt-

age present at the shunt resistor to a 1.65V DC level. Hence the voltage applied to the

dsPIC DSC ADC channel varies within 0-3.3V. The offset is controlled by R59, R60,

R38 and U13D. R35 and C34 filter out the high-frequency noise.

The same topology is used for the phase M2.

DC Bus Current Feedback, a shunt resistor is located between the shunt resistors of

side switches M1 and M2 and the “-DC bus”. A simple differential amplifier circuit is

used as shown in the schematic. The operation of the circuit used for sensing the DC

bus current is described as follows:

The current is sensed using the shunt resistor R95 and the operational amplifier

MCP6024 (U13C); R51, R52 and R49 set the gain. R58 shifts the voltage present

at the shunt resistor to a 1.65V DC level. Hence the voltage applied to the dsPIC

DSC ADC channel varies within 0-3.3V. The offset is controlled by R59, R60, R58

and U13D. R54 and C42 filter out the high-frequency noise.

Note: It is possible to select any of these feedback signals using jumpers J12, J13

and J14, please refer to Section 4.2.8 “User Interfaces” for more

information.

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