Jameco Electronics 3000 ユーザーズマニュアル

The following mechanisms contribute to the current consumption of the Rabbit 3000 
while it is operating.

1. A current proportional to voltage and clock frequency that results from the charging of 

internal and external capacitances. At 3.3 V (see (2) below) approximately 57% of the 
current is due to charging and 43% is due to crossover current.

2. A crossover current that is proportional to clock frequency and to the overdrive voltage 

V

c

  = V × [(V/2) – 0.7], where V is the operating voltage of the Rabbit 3000. The cross-

over current results from a brief short circuit when both the P and N transistors of a 
CMOS buffer are turned on at the same time. This component drops as the voltage 
drops, and becomes negligible at 1.4 V.

3. The current consumed by the built-in main oscillator when turned on. This current is 

also proportional to V

c

, and is equal to 1 mA at 3.3 V.

4. The current drawn by the logic that is driven at the oscillator (crystal frequency). This is 

considered distinct because it varies with the crystal frequency, but is not reduced when 
the clock frequency is divided. This current becomes zero when the main oscillator is 
turned off, and is 2.5 mA at 3.3 V when the crystal frequency is 14.7 MHz. This current 
is divided between capacitive and crossover components in the same manner as the cur-
rents in (1) and (2) above.

All of the above currents can be combined according to the following formula:

I

total

 (mA)  = 0.32 × V × f  + 0.23 × Vc × f  + 0.30 × Vc + 0.029 × V × fc + 0.025 × Vc × fc

where V = the operating voltage of the Rabbit 3000, V

c

 = V × [(V/2) – 0.7], f

c

 = frequency 

of crystal oscillator in MHz, and f = clock frequency in MHz.