Other Parts Discussed in Thread: AM3352
The design I'm working on is based on the TMDSSK3358 starter kit schematics. The board will have a +5V supply derived from +24V available in an industrial system. RTC functionality is not required.
I've made the following changes to disable the RTC based on reviewing posts to this forum & the AM335x / TPS65910A3 data sheets. I ask for a review to assure that I haven't missed any details:
1. Eliminate the standalone RTC LDO used on the TMDSSK3358 schematics, instead using the TPS65910A3 RTC LDO to source the VDDS_RTC supply required by the AM3352.
2. Eliminate the RTC reset circuit & tie RTC_PWRONRSTn to VSS
3. Disable the AM3352 internal RTC LDO by connecting RTC_KALDO_ENn to VDDS_RTC & connecting CAP_VDD_RTC to VDD_CORE. The 1uF bypass capacitors on CAP_VDD_RTC is eliminated, but the 10nF bypass cap remains at the VDDS_RTC ball.
4. Eliminate the RTC crystal and its capacitive load. Connect VSS_RTC to VSS and leave RTC_XTALIN & RTC_XTALOUT floating
5. EXT_WAKEUP is tied to VSS
5. From the AM335x datasheet Figure 4-5, PMIC_POWER_EN is non-functional with the RTC disabled. To generate the start condition for the TPS65910A3 as the +5V supply increases, the PWRHOLD signal is pulled up to the VCC7 input voltage by a 10K resistor. Also, PWRON is pulled up to the VCC7 input voltage by a 10K resistor as well (there will be no push-button to start the system).
I'm assuming that the TPS65910A3 RTC LDO will be able to source the AM3352 VDDS_RTC requirements since the RTC logic is held in reset. Also, I don't believe we are sacrificing any power-down sequencing functionality by not using the PMIC_POWER_EN signal. Are these assumptions true?
Thanks for your time.
Regards,
Russ
