Figure 6-12 shows the recommended crystal circuit for OSC1 of the ZCE package and Figure 6-13 shows the recommended crystal circuit for OSC1 of the ZCZ package. TI recommends that preproduction PCB designs include the two optional resistors Rbias and Rd in case they are required for proper oscillator operation when combined with production crystal circuit components. In most cases, Rbias is not required and Rd is a 0-Ω resistor. These resistors may be removed from production PCB designs after evaluating oscillator performance with production crystal circuit components installed on preproduction PCBs.
The RTC_XTALIN terminal has a 10- to 40-kΩ internal pullup resistor which is enabled when OSC1 is disabled. This internal resistor prevents the RTC_XTALIN terminal from floating to an invalid logic level which may increase leakage current through the oscillator input buffer.