DM300022 Microchip Technology, DM300022 Datasheet - Page 26

• Manufacturer Part Number: DM300022
• Description: MODULE PWR DSPICDEM MC1L LV 3PHS
• Manufacturer: Microchip Technology

Specifications of DM300022

• Main Purpose: Power Management, Motor Control
• Embedded: Yes, MCU, 16-Bit
• Utilized Ic / Part: dsPIC33FJxxxMC
• Primary Attributes: 3-Phase Low Voltage Power Module
• Secondary Attributes: Motion Sensor Inputs: Hall Sensors or Optical Encoder
• Silicon Manufacturer: Microchip
• Silicon Core Number: DsPICDEM MC1L
• Kit Application Type: Power Management - Motor Control
• Application Sub Type: 3 Phase Motor
• Silicon Family Name: Piccolo
• Rohs Compliant: Yes
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

dsPICDEM™ MC1L 3-Phase Low Voltage Power Module
DS70097A-page 20
1.5.6
1.5.6.1
In many applications, the cost of isolated current transducers is prohibitive or the
isolation is not required. In these instances, it is common practice to use resistive
shunts. The shunts can be placed in series with the output connections, but this
inevitably requires the use of level-shifting and the creation of floating power supplies.
Therefore, it is more usual to have shunts referenced to the same potential as the low
voltage power supplies which is invariably the -DC bus. The disadvantage of using
shunts referenced to the low side is that the feedback information is clearly only
available during certain portions of the PWM cycle. In order to extract the required
information, the shunts must be sampled at precise intervals. This feature has been
allowed for in the dsPIC device by the inclusion of sample and hold amplifiers in the
ADC module that can be triggered from the PWM module (see the dsPIC30F Family
Reference Manual for details).
On high voltage low power systems, it may be possible to use shunts of high enough
value to have sufficient voltage for direct input to an ADC. More commonly, the
dissipation in the shunt dictates the use of low resistance values and appropriate
amplification. If too high, the voltage drop across the shunt can also cause problems
for driving the power transistors. For low gains, it may be possible to use single ended
amplification. Differential amplification is required as the gains increase in order to
provide a signal of sufficient quality and accuracy.
The Microchip MCP6022 (dual) and MCP6024 (quad) parts have been used in the
design for providing the differential amplification. They are an ideal choice for the
following reasons:
• Low power consumption (1 mA typical / amp) - this is especially important where
• Low offset voltage (0.5 mV max.).
• Rail-rail inputs and outputs.
• No gain inversion with negative inputs - this is important as it is common for the
• High gain bandwidth product (10 MHz typical) - this is often a more important
Note that in applications requiring less gain and/or slower speed of response, the
MCP602/604 family offers a good alternative with even lower power supply
consumption.
1.5.6.2
A shunt is located between the source of the low side switches (e.g., Q4) and the -DC
bus in every leg of the inverter. A simple differential amplifier circuit is used as shown
in Appendix A Sheet 3. The operation of the circuit used for the RED phase leg is
described below:
• U24-A – One quarter of the MC6024 op amp.
• R94, R99 and C34 – These provide a small amount of passive differential filtering.
the power supplies are derived from the DC bus with a resistor/zener network.
amplifier to have negative spikes on it's inputs that occur during switching events
due to the shunt's inductance. Gain inversion can lead to current control instability
and false tripping of protection circuits.
factor in determining the speed of response than slew rate in this application, due
to the requirements to amplify rapidly changing signals of low amplitude.
This helps to reduce input stage overloading of the op amp that would occur due
to spikes of voltage produced by the shunt's self-inductance. Clearly, this has a
beneficial effect on the output signal.
Shunt Feedback (Appendix A Sheet 3)
INTRODUCTION
INVERTER LEG SHUNT RESISTOR FEEDBACK
© 2003 Microchip Technology Inc.