AR# 1520: XC2000L/XC3000L/XC4000L: Estimating power consumption for 3.3V Devices (2000L, 3000L, 4000L)
AR# 1520
XC2000L/XC3000L/XC4000L: Estimating power consumption for 3.3V Devices (2000L, 3000L, 4000L)
Description
Keywords: power consumption, xc2000, xc3000, xc4000, 3.3V
Urgency: standard
Description This is a guideline for estimating power consumption for our low voltage (3.3V) devices. For more information regarding estimating power consumption in FPGAs please refer to the 1996 Databook.
Solution
Since our 3.3 volt devices have the same architecture as thier 5V counterparts and almost all power (except Icco) is dynamic, the power changes with the square of the supply voltage.
That means, at nominal 3.3 V, the power is 43.6 percent of the power at nominal 5 V. If you use the mac commercial values, 3.6 V and 5.25 V, then it is 47 percent.
Based on this information, the following figures may be used to estimate possible power consumption of a design :
all units given in "milliwatts per million transitions per second"
"CLB" = one CLB driving three local interconnects
"Output" = one output driving 50 pF
"Clock" = one global clock line connected to all flip-flops
"Longline" = one split Longline
"CLB" and "Output" are independent of device size.
"Clock" is proportional to the number of CLBs, i.e. to the gate count.
"Longline" power is proportional to the square root of the number of CLBs, or the square root of the gate count.
Note : For very low power watch out for the high Icco of the XC3100L ( due to gate pumping ), and the ficticiously high Icco of the XC5200L, due to anticipated future gate pumping.