AN1914 Freescale Semiconductor / Motorola, AN1914 Datasheet - Page 12

• Manufacturer Part Number: AN1914
• Description: 3-Phase BLDC Motor Control with Sensorless Back EMF Zero Crossing Detection Using DSP56F80x
• Manufacturer: Freescale Semiconductor / Motorola

System Design Concept
4.
4.1 System Specification
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The voltage drop resistor is used to measure the DC-bus current which is chopped by the PWM. The
obtained signal is rectified and amplified (0-3.3V with 1.65V offset). The internal DSP A/D converter
and Zero Crossing detection are synchronized with the PWM signal. This synchronization avoids
spikes when the IGBTs (or MOSFETs) are switching and simplifies the electric circuit.
The A/D converter is also used to sense the DC-Bus Voltage and drive Temperature. The DC-Bus
voltage is divided down to a 3.3V signal level by a resistor network.
The six IGBTs (copack with built-in fly back diode) or MOSFETs and gate drivers create a compact
power stage. The drivers provide the level shifting that is required to drive high side switch. PWM
technique is used to the control motor phase voltage.
The system was designed to meet the following performance specifications:
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System Design Concept
Control technique incorporates
— sensorless BEMF Zero Crossing commutation control
— closed loop without current loop
— bi-directional rotation
— motoring mode
Targeted for DSP56F803/805EVM platforms
Running on one of three optional board and motor hardware sets
DSP56F80x MC PWM Module in Motor Control Applications
Freescale Semiconductor, Inc.
Figure 3-8. The Zero Crossing Detection
For More Information On This Product,
Go to: www.freescale.com