Cerebot MC7™ Board Reference Manual
Copyright Digilent, Inc. All rights reserved.
Other product and company names mentioned may be trademarks of their respective owners.
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This regulator is capable of providing a maximum of 500mA of current. The DSPIC33 microcontroller will use
approximately 90mA when running at 40 MIPS. The other circuitry on the board will draw 10-20 mA. The
remaining current is available to provide power to attached Pmods and I
2
C devices. The voltage regulator is on the
bottom of the board, below Pmod connector JA, and will get warm when the amount of current being used is close
to its limit.
The Cerebot MC7 can provide power to any peripheral modules attached to the Pmod connectors, JA-JC, and to I
2
C
devices powered from the I
2
C daisy chain connectors, J6 and J8. Each Pmod connector provides power pins that
can be powered from either the switched main power bus, BRD5V0, or regulated voltage, BRD3V3, by setting the
voltage jumper block to the desired position. The I
2
C power connectors only provide regulated voltage, BRD3V3.
4
Half-Bridge Circuits
The Cerebot MC7 circuit provides four half bridges. A half bridge is made up of two stacked transistors such that
the high side transistor can source current from the motor power supply and the low side transistor can sink
current to the supply ground.
Each half bridge is made up of an On Semiconductor NTMD4820N dual N-FET to provide the transistors and a
Microchip MCP14700MF FET driver. The FET driver provides a high side transistor drive input and a low side
transistor drive input.
The NTMD4820N FETs are rated for a maximum V
DS
of 30V, maximum V
GS
or 20V, and maximum drain current (I
D
)
of 8A at 25°C, 6.4A at 70°C (t<10s) or 6.4A continuous drain current at 25°C and 5.1A at 70°C. For more detailed
information on the NTMD4820N, refer to the device data sheet available at the On Semiconductor web site.
The steady state temperature of the FETs with all four half bridges switching at 50% duty cycle and a load current
of 5A each has been measured to be ~55°C. Operation in some applications may require heat sinking or fan cooling
of the board to maintain continuous operation at the full 5A output current.
The high side and low side drive inputs for each half bridge are connected to PWMH and PWML outputs from the
Motor Control PWM module in the dsPIC microcontroller. The Motor Control PWM module is an advanced pulse
width modulation generator optimized for motor control applications. This PWM unit provides eight outputs
arranged as four high and low side drive pairs for controlling four half bridge circuits.
The half bridges can be operated independently, in pairs to form two h-bridges, or in other combinations using the
Motor Control PWM module.
Connector J20 is used to provide the power supply voltage for the high side of the half bridges, and therefore
powers whatever external load is being controlled by the board. This is a screw terminal connector on the left side
of the board. A power supply or battery of 5V-24V can be used, with a maximum continuous current of 10A.
The half bridge connections between the bridge output signals and the Motor Control PWM module are
configured in the following way:
VMOT1
PWM1H, PWM1L
VMOT2
PWM2H, PWM2L
VMOT3
PWM3H, PWM3L
VMOT4
PWM4H, PWM4L
