Figure 11. Capacitance Measurement Using Comp2; Equation 1; C = - T - STMicroelectronics AN3248 Application Note

Capacitance measurement

Figure 11. Capacitance measurement using COMP2

At the moment where the input voltage crosses the threshold and the COMP2 output
switches to high level, the charge function is given by

Equation 1

where "tc" is the time when the input voltage crosses the threshold
Using Equation 1
Equation 2
Usually R, the threshold, and V
to solving for
14/19
Threshold
the capacitance value can be computed by
⁄
C = – t
are constant, so, measuring the capacitance is reduced
DD
Equation 3.
Doc ID 17758 Rev 1
Equation
( ( ⁄
VDD 1 exp -tc
= –
( × ( ⁄ (
R ln 1-threshold V
1.
) )
T
Equation 2.
) ) )
DD
AN3248