Application Note
33 of 38
001-86233 Rev. *I
2021-11-04
PSoC™ 4 MCU low
-power modes and power reduction techniques
Measuring current with a DMM
10
Measuring current with a DMM
When using a DMM to measure the current, it is important to know the value of the shunt resistor in the DMM.
DMMs have one or more (shunt) resistors between the current inputs. These resistors can range from less than
an ohm to more than 10 k
Ω
. There is no standard value for the shunt resistor between brands or even models
from the same
vendor. It is important to review your meter’s manual and learn the value of the shunt resistor
because there is always a voltage drop across this shunt. This means that the
PSoC™
4 MCU device does not see
the same voltage as that which you are supplying.
If the shunt resistor in your meter is 1
or less, you will see only a few millivolts of drop when measuring
PSoC™
4 MCU current, and you can ignore it. If the shunt resistor is 1 k
, which some vendors use for low-
current measurements, a 1-mA current will result in a drop of 1 V. Also, when changing ranges, be careful that
the DMM does not do a break-before-make, or the power will be cycled and your project will be reset.
For extremely low currents in deep sleep, hibernate, and stop modes, a good technique is to use a zero- or low-
resistance shunt until the device enters low-power mode. After entering low-power mode, the code should
keep the device in that mode and switch to a high-resistance shunt for current measurement.
As an alternative to relying on the DMM shunt, both kits include a place for a shunt resistor. CY8CKIT-049-42xx
has a zero-ohm shunt (R6). This can be replaced by a small resistor and measurement of the voltage across the
shunt with a voltmeter. You can then easily determine the current. A shunt between 1
and 100
should work
well for most applications. CY8CKIT-042 also has place for a shunt resister (R6) next to J13.
10.1
Approximating the power consumption
The device datasheet and
PSoC™
Creator component datasheets provide sufficient information to estimate the
power consumption for a given project. To simplify this process, a spreadsheet has been provided that includes
typical power requirements for a wide range of internal components. This spreadsheet,
PSoC4_Power_Estimator.xlsx
, is located on the
. Because every project is different, the power
calculation provided by this spreadsheet is only an estimate, but it should be close enough to provide good
feedback before your design is complete. There are several tabs in the spreadsheet; make sure you read the
“Instructions” tab before entering your data.
