STWLC04

Application information

DocID029626 Rev 2

13/18

4.2.3

Load modulation capacitor selection (CM1, CM2)

These capacitors fulfill the backscatter modulation of the communication from the receiver

to the transmitter. X5R dielectrics type capacitors are suitable for this purpose.

4.2.4

Feedback resistor divider component selection (RFB1, RFB2)

Feedback voltage divider gives the ratio between the desired step-down converter output

0.1% or 0.5% precision.

4.2.5

Rx NTC circuit component selection (RNTC, R1)

To protect the receiver coil from overtemperature, the STWLC04 is equipped with a

comparator input. If the input voltage crosses a certain level, the STWLC04 reacts

terminating the power transfer and sending an interrupt to the host system

– depending on

common resistor divider. The divider can be supplied from LDO1 (VA pin) filtering

capacitor.

4.2.6

Soft-start capacitor selection (C10)

The soft-start capacitor C10 connected to COMP pin influences the ramp-up time of the

nominal voltage is given by the following equation:

Equation 3:

Example: 470 nF ~ 560 ms

4.2.7

External supply transistor selection

by the external dual P-channel transistor back-to-back connected so to avoid the leakage