2.2.4 Typical 3V Stand-Alone Application

Figure 2-6 shows a stand-alone key fob application circuit running from a 3V lithium cell. The DC-DC Converter cannot be used in 3V mode, and, therefore, it must be short-circuited by connecting VS to DCDC2.

The ATA5835 stays in OFFMode until one of the NPWRON ports, PC1 to PC5, is pulled to ground level, waking up the circuit. The NPWRON ports, PC1 to PC5, have internal 50 kΩ pull-up resistors and can be left open if not used.

The user application software within the 20-Kbyte Flash is used to control the transceiver together with the ROM firmware.

In this application, LEDs can be connected to PB7 and PB4. At PB4, an additional pull-down resistor is recommended in parallel to prevent transverse currents in OFFMode.