18.104.22.168 Power Management and Supervisory Circuit Solutions
LDO selection depends on the total power consumed in the end application. Go to the Power Management page for a list of TI power management ICs. Click the Reference designs tab for specific power management reference designs.
A. Upon power up, SYSCLKOUT is OSCCLK/4. Because both the XTIMCLK and CLKMODE bits in the XINTCNF2 register come up with a reset state of 1, SYSCLKOUT is further divided by 4 before it appears at XCLKOUT. This explains why XCLKOUT = OSCCLK/16 during this phase. Subsequently, boot ROM changes SYSCLKOUT to OSCCLK/2. Because the XTIMCLK register is unchanged by the boot ROM, XCLKOUT is OSCCLK/8 during this phase.
B. After reset, the boot ROM code samples Boot Mode pins. Based on the status of the Boot Mode pin, the boot code branches to destination memory or boot code function. If boot ROM code executes after power-on conditions (in debugger environment), the boot code execution time is based on the current SYSCLKOUT speed. The SYSCLKOUT will be based on user environment and could be with or without PLL enabled.
C. See Section 5.9.2 for requirements to ensure a high-impedance state for GPIO pins during power up.