AN1627 Freescale Semiconductor / Motorola, AN1627 Datasheet - Page 21

• Manufacturer Part Number: AN1627
• Description: Low Cost High Efficiency Sensorless Drive for Brushless dc Motor Using MC68HC (7)05MC4
• Manufacturer: Freescale Semiconductor / Motorola

6.1.2
In a star connected motor winding, the phase current can be sensed on the DC-Bus rail as each motor
phase pair is energised. The voltage drop resistor (0,6Ohm/2W) is used to measure the DC-Bus current
(0-4A), which is chopped by the PWM. The obtained signal is rectified and amplified (0-5V). The internal
A/D converter is synchronized with the PWM signals (see Figure 5-5.). The current signal is converted
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switching and simplifies the electric circuit. The over-current limit (3,6A) is detected by a comparator.
This output is used to directly switch off the IGBT’s and for the IRQ interrupt input.
6.1.3
The DC-Bus voltage is divided down-to a 5V signal level using a serial resistor network. This signal is
used for over-voltage and under-voltage detection.
6.1.4
There are six MGP4N60ED IGBT’s (copack; with built-in fly back diode) driven by three IR2112 high
voltage gate drivers.
Switching times, saturation voltage, and short circuit time of the IGBT’s have been optimized for motor
drives. In addition, the gate threshold voltage is higher than usual for MOS gated power devices. The
higher threshold eliminates the need for negative gate drive.
The high voltage driver IC's are designed to directly drive the gates of power MOS devices. They provide
the level shifting that is required to drive high side bridge circuits commonly used in motor drives and
other power applications. They are capable of withstanding floating supply offset voltages up to
600 volts. The Shut-down input of the IR2112 is used to switch off all IGBT’s when over-current detection
is activated.
Detailed information about the power stage board can be found in the application note: AN1590 - “High
Voltage Medium Power Board for Three Phase Motors”.
AN1627
REV 0.2
s before the end of the PWM “ON-time”. This synchronization avoids spikes when the IGBT’s are
Current Sensing
Voltage Sensing
Power Devices
Freescale Semiconductor, Inc.
For More Information On This Product,
Figure 6-3.
+DC-Bus
+300V
-DC-Bus
0V
Go to: www.freescale.com
10k 10k
+15V
AD_Volt
15k
MC34074
Current & Voltage Sensing
0R6
+5V
33k
1M
Power Stage
MC34074
5k
4k7
33k
LM339N
10k
+5V
AD_Curr
Over-Curr
MOTOROLA
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