A42MX24-2PQ160 Datasheet, PDF (14/143 Pages) Microsemi Corporation – 40MX and 42MX FPGA Families

40MX and 42MX FPGA Families
Power Dissipation
The general power consumption of MX devices is made up of static and dynamic power and can be expressed with the
following equation.
General Power Equation
P = [ICCstandby + ICCactive] * VCCI + IOL* VOL* N + IOH * (VCCI – VOH) * M
where:
ICCstandby is the current flowing when no inputs or outputs are changing.
ICCactive is the current flowing due to CMOS switching.
IOL, IOH are TTL sink/source currents.
VOL, VOH are TTL level output voltages.
N equals the number of outputs driving TTL loads to VOL.
M equals the number of outputs driving TTL loads to VOH.
Accurate values for N and M are difficult to determine because they depend on the family type, on design details, and
on the system I/O. The power can be divided into two components: static and active.
Static Power Component
The static power due to standby current is typically a small component of the overall power consumption. Standby
power is calculated for commercial, worst-case conditions. The static power dissipation by TTL loads depends on the
number of outputs driving, and on the DC load current. For instance, a 32-bit bus sinking 4mA at 0.33V will generate
42mW with all outputs driving LOW, and 140mW with all outputs driving HIGH. The actual dissipation will average
somewhere in between, as I/Os switch states with time.
Active Power Component
Power dissipation in CMOS devices is usually dominated by the dynamic power dissipation. Dynamic power
consumption is frequency-dependent and is a function of the logic and the external I/O. Active power dissipation
results from charging internal chip capacitances of the interconnect, unprogrammed antifuses, module inputs, and
module outputs, plus external capacitances due to PC board traces and load device inputs. An additional component
of the active power dissipation is the totem pole current in the CMOS transistor pairs. The net effect can be associated
with an equivalent capacitance that can be combined with frequency and voltage to represent active power dissipation.
The power dissipated by a CMOS circuit can be expressed by the equation:
Power (µW) = C_EQ * VCCA2 * F(1)
where:
C_EQ = Equivalent capacitance expressed in picofarads (pF)
VCCA = Power supply in volts (V)
F = Switching frequency in megahertz (MHz)
Equivalent Capacitance
Equivalent capacitance is calculated by measuring ICCactive at a specified frequency and voltage for each circuit
component of interest. Measurements have been made over a range of frequencies at a fixed value of VCC.
Equivalent capacitance is frequency-independent, so the results can be used over a wide range of operating
conditions. Equivalent capacitance values are shown below.
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