DA1641.004

1 February, 2019

7 (14)

APPLICATION INFORMATION (continued)

EXAMPLE 2: Capacitance increase sensing





 (shorted)

=113.22k

values. The resistor value rounding to standard series values can be done only in the next step.

  1.5M

  110k

/1.5M+1)=3.43pF OK! (very close to target 3.45pF)

Capacitor andta resistor values for charge pump and piezo driver

The external CIN, CF1, CF2 and COUT capacitors must be low loss (low ESR) ceramic capacitors.

Recommended resistor and capacitor values are shown in the table 2.

Table 2. Recommended capacitor and resistor values

Capacitor

Nominal value

Voltage rating

CIN

10

F (min 1F)

min 6.3V

CF1, CF2

100nF

min 6.3V

COUT

100nF

min 16V

CS

470pF

min 16V

RB

1.5M



RF

200k



Note: Some capacitor dielectric materials such as Y5V have strong voltage dependence. The actual capacitance

value may reduce remarkably when operating near rated voltage. In such case the nominal capacitor value should

be chosen larger to compensate the voltage dependence.

The input (CIN), flying (CF1, CF2) and output (COUT) capacitor value selections have influence on output (VOUT)

ripple and disturbances at supply voltage input (VIN). Table 3 shows alternative capacitor value selections in

different applications. In battery operated applications it is recommended to use CIN=10

F which keeps the start-

up inrush current low.

Table 3. Capacitor value selections in different applications

CIN

CF1-2

COUT

Application

1µF

100nF

100nF

Minimum size layout

10µF

100nF

100nF

Low input disturbances

10µF

100nF

1µF

Low input disturbances and low output ripple

and charge pump output capacitor (COUT). Then the output ripple can be reduced by choosing output capacitor

value which is much larger relative to piezo capacitance value. However, note that large output capacitor also

lengthens output voltage rise time and increases inrush current during start-up.