THVD4431 has integrated high-efficiency and low-noise charge pump to generate large output voltages for RS-232 signals. Charge pump consists of a voltage doubler and an inverter to regulate the voltage to nominal ± 5.5 V or to ±9.5 V for 3.3 V or 5-V V_CC operation respectively. Charge pump needs four external ceramic capacitors (2 flying capacitors and 2 storage capacitors) and allows for single supply operation for RS-232. For a generic description of RS-232 charge pump operation, please refer to the blog: How the RS-232 transceiver’s regulated charge-pump circuitry works.