Power Estimation and Management
Lattice Semiconductor
for LatticeECP/EC and LatticeXP Devices
12-19
5. Reducing the voltage swing of the I/Os where possible.
6. Using optimum encoding where possible. For example, a 16-bit binary counter has, on average, only 12%
Activity Factor and a 7-bit binary counter has an average of 28% Activity Factor. On the other hand, a 7-bit
Linear Feedback Shift Register could toggle as much as 50% Activity Factor, which causes higher power
consumption. A gray code counter, where only one bit changes at each clock edge, will use the least
amount of power, as the Activity Factor would be less than 10%.
7. Minimize the operating temperature, by the following methods:
a. Use packages that can better dissipate heat. For example, packages with lower thermal impedance.
b. Place heat sinks and thermal planes around the device on the PCB.
c. Better airflow techniques using mechanical airflow guides and fans (both system fans and device
mounted fans).
Power Calculator Assumptions
Following are the assumptions made in the Power Calculator:
1. The Power Calculator tool is based on equations with constants based on room temperature of 25°C.
2. The user can define the Ambient Temperature (Ta) for device Junction Temperature (Tj) calculation based
on the power estimation. Tj is calculated from user-entered Ta and power calculation of typical room tem-
perature.
3. The I/O power consumption is based on output loading of 5pF. Users have ability to change this capacitive
loading.
4. The current version of the Power Calculator allows users to get an estimate of the power dissipation and
the current for each type of power supplies, that are VCC, VCCIO, VCCJ and VCCAUX. For VCCAUX, only static
ICCAUX values are provided in the Calculator.
Additional VCCAUX contributions due to differential output buffers, differential input buffers and reference
input buffers must be added per pair for differential buffers or per pin for reference input buffers according
to the user's design. See the equation given in this technical note for Total DC Power (ICCAUX).
5. The nominal VCC is used by default to calculate the power consumption. Users can choose a lower or
higher VCC from a list of available values. For example, the nominal VCC of 1.2V is used by default for the
LatticeECP/EC and LatticeXP families of devices.
6. The current versions also allows users to enter an airflow in Linear Feet per Minute (LFM) along with the
Heat Sink option to calculate the Junction Temperature.
7. The default value of the I/O types for the LatticeEC and LatticeXP devices is LVCMOS12, 6mA.
8. The Activity Factor (AF) is defined as the toggle rate of the registered output. For example, assuming that
the input of a flip-flop is changing at every clock cycle, 100% AF of a flip-flop running at 100MHz is 50MHz.