Low-Power Design Considerations
AN66308 - CY8CMBR2044 CapSense® Design Guide, Doc. No. 001-66308 Rev. *F
36
Average Power (P
AVE
)
Equation 12
Where:
I
AVE
= average current
Example Calculation
As an example of how to calculate average power, consider a CapSense user interface on a bluetooth headset with
three well-designed buttons. The C
P
for all three buttons is between 10 pF and 22 pF. The buttons are scanned at a
rate of 507 ms.
The scan time can be calculated using a sensor constant of 2 for all three buttons and Equation 13:
Equation 13
The average current in NO TOUCH state is calculated as follows using Equation 14 and the maximum values for
I
SLEEP
and I
ACTIVE
:
Equation 14
The average current in TOUCH state is calculated as follows using Equation 15:
Equation 15
To calculate the average current, assume your headset receives 50 calls in an 8-hour business day and the user
touches a CapSense button every 20 seconds during each call. This means your design operates in a TOUCH state
about 1.8 percent of the 8 hours during which the headset is turned on. The average current consumption of the
design is calculated as follows using Equation 16:
Equation 16
Assuming this design does not utilize deep sleep mode and that it operates at 1.71 V the average power is calculated
as follows using Equation 17:
Equation 17
