DA6241.005

31 January, 2019

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Capacitor and resistor values

Capacitors must be ceramic type with low ESR and meeting sufficient minimum voltage ratings. The CIN input, CF1

and CF2 flying capacitors see one VIN voltage and they have minimum 6.3V voltage rating. The COUT capacitor

sees 2 x VIN voltage in 2x configuration and 3 x VIN voltage in 3x configuration. Then the COUT capacitor should

have minimum 9V voltage rating in the 2x configuration and minimum 16V rating in the 3x configuration. See table

2 for recommended capacitor and resistor values.

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 9V in 2x configuration

min 16V in 3x configuration

C1

470p

min 9V in 2x configuration

min 16V in 3x configuration

R1

1.5M

R2

200k

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

value may drop 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.