2
AVR430
8124C-AVR-10/08
2 Hardware overview
Please refer to schematics, layout and BOM available at http://www.atmel.com.
The MC300 motor control driver board is a power stage board intended for driving
BLDC and stepper motors. It has four half-bridges with independent control of high
and low sides. Each bridge has options for filtered/voltage divided feedback from its
output (EMF) and shunt resistor. There is also feedback from a common shunt
resistor, Vmotor (Vm) and Vneutral (Vn - center tap motor windings).
Four 8-pin 2,54mm (100mil) horizontal female pin headers on the left side of the
board form a system connector for device boards.
The board has an adjustable voltage regulator for Vcc, 3.3V or 5V, and this voltage is
available on the system connector. A 5V regulator powers the Hall sensors. Vm, Vin
and Vcc each have their own LED to indicate power.
2.1 Specifications
MC300 maximum ratings with components as delivered:
Input:
•
Vin: 10 – 20VDC
•
Vm: 0 – 40VDC, Im
max
= 6A
Output ratings:
•
Vcc = 3.3/5V, I
max
= 0.5A
•
Vha = 5V, I
max
= 0.1A
The driver stage consists of four half-bridges capable of 40V / 30A (Warning! Other
components such as shunt resistors limit the maximum current to 6A).
2.1.1 Necessary precautions
The gate voltage to the high side MOS is powered by a bootstrap capacitor. To
sustain the voltage over this capacitor the
high side must be turned off for a short
time on a regular basis
, allowing the capacitor to be recharged via a diode. Failing
to do so, for example. by keeping the high side permanently on, will cause the gate
voltage on the high side MOS to drop and the internal resistance to increase. If a high
current is going thru the high side MOS at this point the transistor will overheat and be
destroyed. The fuse will not prevent this from happening.
