Introduction to Microcontrollers Lab Manual - Microchip

9.1 OBJECTIVE
9.2 PRE-LAB
Lab 9. Power Management
Learn to consider power consumption issues for embedded designs.
9.2.1 Reference Material
• PIC24FJ256GB110 Family Data Sheet (DS39897)
• 16-Bit MCU and DSC Programmer’s Reference Manual (DS70157)
• PIC24F Family Reference Manual – Section 6. Oscillator (DS39700)
• PIC24F Family Reference Manual – Section 10. Power Saving Features
(DS39698)
• PIC24F Family Reference Manual – Section 14. Timers (DS39704)
• AN1267 nanoWatt and nanoWatt XLP Technologies: An Introduction to
Microchip’s Low-Power Devices (DS01267)
9.2.2 Power
LABS
Every electronic system requires power to run. For systems powered by batteries, it is
important to minimize the amount of power required – this extends battery life or allows
for the use of a smaller battery. As the number of electronic systems continues to grow,
it is becoming more and more important to reduce the power consumption and the
impact on our planet. The concepts presented in this lab are a first step to understanding
this complex topic.
There are two components to the total power consumption of a system: static power
consumption and dynamic power consumption.
Static power is the current consumed when the main clock is disabled. In general, this
includes supervisory circuitry as well as logic required to turn the main clock on due to
some external condition. This also includes the leakage currents of the device transistors
themselves. In general, this is very low and fixed for a given microcontroller device.
Dynamic power is the current consumed by the switching of digital logic. The higher the
frequency, the more switches occur in a given amount of time and more power is consumed.
Dynamic power tends to be much larger than static power for embedded systems
and the design of the software can greatly influence this factor. Thus, this lab will
focus on methods to reduce the dynamic power.
9.2.3 Calculating Power
The dynamic power of a circuit can be calculated with the following equation:
PDYN = C•V2•F Where PDYN is the power consumed in Watts, C is the capacitance being switched per
clock cycle in Farads, V is the amplitude of the voltage in Volts, and F is the frequency
of the switching in Hz. This equation is for one switched node. The total dynamic power
consumed by a circuit is simply the sum of the dynamic power consumed for each node
in the circuit.
2011 Microchip Technology Inc. DS51963A-page 63