Mobile Device Power Monitor Manual - GitHub Pages

12
Powering-up and Powering-down a Mobile Device
To power-up the device, first set the Vout voltage. The voltage can be set from 2.1 V to 4.5
V in .01 V increments. The maximum voltage of a lithium battery is usually 4.2 V, so set
the Vout voltage somewhere between 3.3 V and 4.2 V.
To enable the power, click the Vout Enable button, to disable the power, click the Vout
Disable button.
Figure 5: below shows the location of the Vout Enable, which toggles when it is clicked to
the Vout Disable button.
Figure 5: Vout Enable and Vout Disable button
The voltage at the red and black terminals is never exactly at the programmed voltage. This
is because there is an internal 0.056 Ω sense resistor in series with the regulator. For
example, if the device is drawing 1 A when Vout equals 3 V, expect to see (3 - 1*.056) =
2.944 V. Figure 10: below shows this sense resistor in series with the regulator, in relation
to the red and black terminals.
Figure 6: Sense resistor in series with the regulator, in relation to the red and black
terminals
There is resistance in the wiring that can lower the voltage at the device. The resistance of
the wiring plus the sense resistor is similar to the resistance of the lithium battery in the
device; batteries are usually about 0.12 Ω.
The resistance of 20 gauge wire is 0.012 Ω/ft, so if the cables are 20 gauge, and 1 foot in
length, that adds another 0.024 Ω, in addition to the contact resistance.