DSP Hotline TechBits: 'LC31 Power Measurements

'LC31 Power Measurements

Test settings:

clock frequency = 33.3 MHz, but can be scaled to any frequency.
V_cc = 3.3 volts at the pins of the DSP, but can be scaled to 5v.
'C31 silicon revision 5.X
- (Note these measurements were not performed on the latest silicon:
  silicon revision 6.X)

If you are interested in calculating I_cc very accurately in LOWPOWER mode, I_q can be broken down. The two components are clock current (I_clk), which is unaffected by LOWPOWER. And internal logic current I_ql, which is affected by clock mode. Expressing this as an equation:

I_q = I_clk + I_ql

Power-down Modes Current Consumption:

In MAXSPEED running in IDLE mode with 33.33 MHz clock
- I_q = 33.3 mA
  I_clk = 5.2 mA,
  therefore I_ql = 28.1 mA
In LOPOWER running in IDLE mode with 33.33 MHz clock
I_q = 7.0 mA
I_clk = 5.2 mA
therefore I_ql = 1.8 mA
The ratio in this case is very close to 16:1.

Current Consumption For Various Operations:

Clock Speed	Current Parameter	mA	Notes
MAXSPEED	I_reset	39.0	Device in reset.
	I_q	33.3	Fetching program from internal RAM executing IDLE instruction.
	I_q+I_ops	59.8	Fetching program from internal RAM executing branch to self instruction.
	I_q+ I_ops+ I_ext	125.4	Fetching program from internal RAM executing a store instruction of 5A5A5A5Ah to external memory. C_ext= 0pF
	I_q+ I_ops+ I_ext	187	Same as previous, but adjusted for 80pF loading on both busses.
	I_q+I_ops	45.4	Code fetched from on-chip bootload ROM. INT1,2,3 not driven
	I_q+ I_ops+ I_SP	49.7	Code fetched from on-chip bootload ROM, INT3 driven, Serial Port active.
	Adding DMA and Serial Port to above data adds approximately 10mA.
LOPOWER	I_q	7.0	Fetching program from internal RAM executing IDLE instruction.
	I_q+I_ops	8.5	Fetching program from internal RAM executing branch to self instruction.
	I_q+ I_ops+ I_ext	13.7	Fetching program from internal RAM executing a store instruction of 5A5A5A5Ah to external memory. C_ext= 0pF
		17.6	Same as previous, but adjusted for 80pF loading on both busses.
		92.8	Mean value of FFT code running from internal memory and accessing external memory.
		105.2	Adding 3-standard deviations from the mean value of the FFT code running from internal memory and accessing external memory.
	Adding DMA and Serial Port to above data adds approximately 1mA.
IDLE2	I_clk	5.2	IDLE2 mode executed, external CLKIN still driven
IDLE2	I_clk	50uM	IDLE2 mode executed, external CLKIN not driven