The device features an output enable (OE) and send/receive (DIR) for direction control. A HIGH on OE causes the outputs to assume a high-impedance OFF-state. Inputs include clamp diodes. This enables the use of current limiting resistors to interface inputs to voltages in excess of VCC.

The AM26C31 is an improved replacement for?AM26LS31 IC.?The AM26C31 device is a quadruple differential line receiver for balanced or unbalanced digital data transmission. The enable function is common to all four receivers and offers a choice of active-high or active-low input. The 3-state outputs permit connection directly to a busorganized system. Fail-safe design specifies that if the inputs are open, the outputs always are high. The AM26C31 devices are manufactured using a BiCMOS process, which is a combination of bipolar and CMOS transistors

As of now the CH340g is the cheapest USB to TTL IC in the market with very easy to solder foot print it has solder pitch of 1.27mm and SOIC16 package.

The?CH340 IC?does exactly what you would expect them to do: a full-speed USB device that emulates a standard serial interface, with speeds from 50bps to 2Mpbs. The chip supports 5V and 3.3V, and all the weird modem lines are supported.

Now a days lots of Node MCU, Arduino Nano and USB to TTL Converter Modules have been using this IC.

The high-performance, low cost CP21xx USB to UART bridge family offers a complete plug and play interface solution that includes royalty-free driver suites and a comprehensive design ecosystem that enables customers to speed time-to-market. Crystal-less operation, in-system programming memory and small body size packages reduce cost, simplify design and shorten development time. The CP2102 is a highly-integrated?USB-to-UART Bridge Controller?providing a simple solution for updating RS-232 designs to USB using a minimum of components and PCB space. The?CP2102?includes a?USB 2.0 full speed function controller, USB transceiver, oscillator, EEPROM or EPROM, and asynchronous serial data bus (UART) with full modem control signals in a compact 5 x 5 mm QFN-28 package.

The CP2103 is a highly-integrated?USB-to-UART Bridge Controller?providing a simple solution for updating RS-232/RS-485 designs to USB using a minimum of components and PCB space. The CP2103 includes a USB 2.0 full-speed function controller, USB transceiver, oscillator, EEPROM, and asynchronous serial data bus (UART) with full modem control signals in a compact 5x5 mm QFN-28 package (sometimes called ?MLF? or ?MLP?). No other external USB components are required.