8
AVR430
8124C-AVR-10/08
4 Detailed description
4.1 Power
The MC300 has two power circuits. Vin for powering driver ICs and voltage
regulators, and Vmotor (Vm) for powering the output stage (MOSFETs). The separate
power supply for the motor, Vm, allows the use of motor voltages outside the voltage
range of the driver ICs. This also isolates noise generated by the output stage/motor.
There is a separate ground plane for each power circuit, GND for Vin and GNDmotor
(GNDm) for Vm. This is done to separate the high currents to the motor from the rest.
The ground planes are connected together at one single point, under the J3
connector (shown in Figure 4-1).
A regulated power supply for Vcc is included on the board. The voltage for Vcc is
selectable by J2, if open Vcc = 5V and if set Vcc = 3.3V.
4.1.1 Input
The MC300 can be powered in two ways. With J3, a four pin 3,81mm pitch connector,
separate power supplies can be connected to Vin and Vm. But it is also possible to
power the MC300 from a single DC-Jack connector, J5. J5 is connected to Vin and
Vm via diodes as shown in Figure 4-1. When J5 is used as power input, the supply
voltage must not exceed 20V and maximum current is 5A.
Figure 4-1.
MC300 Power input.
4.1.2 Fuses
Vin is protected by a resettable 0,75A polyfuse (F1). If the current through it exceeds
0,75A, the fuse will heat up and go into a high resistance mode for as long as the load
is retained, and will reset when allowed to cool down.
A socket mounted 6,3A 5x20 mm fuse protects Vm (F2). Using a socket mounted
fuse allows the user to replace and change it easily. When developing software it is
also practical to not power the output stages until correct operation of the software is
ensured, and this can be done by simply removing the fuse.
4.1.3 LEDs
Vcc, Vin and Vm each have their own green LED to indicate if voltage is present. The
Vcc LED (D3) is connected to Vcc by a resistor and hence it will emit less light when
Vcc is 3,3V. Vin and Vm LEDs (D1 and D2) have a constant current sources, so they
have a constant intensity even if Vin or Vm changes.
