We are considering building a board using the BeagleBone as a reference design. Our application would likely require a backup battery to run the RTC in RTC Only mode when power is off/disconnected.
The hardware design guide claims you can use this PMIC in RTC-Only mode:
http://processors.wiki.ti.com/index.php/AM335x_Hardware_Design_Guide#Designing_the_Power_Subsystem
But all other documentation including BeagleBone schematics and TP65217 User Guide has no mention of backup battery:
http://www.ti.com/litv/pdf/slvu551a
Is the hardware design guide wrong, or am I missing something. Can you simply hook up a battery to the LDO input?
Thanks,
Ali
Ali,
Is this a battery-powered or line-powered system?
This would be a line-powered system. The concern is that we would like to run RTC-Only mode off a backup battery if the user disconnects from the mains.
Also do you have any insight into when this part might come out of Preview and how long is TI planning to manufacture this?
You may simply connect your back-up battery to the BAT input on TPS65217B. As long as the line supply is connected, the PMIC will automatically draw power from the line supply (and not discharge the battery). When the line supply is removed, the PMIC will automatically switch over to the backup battery.
During RTC-only mode, only LDO1 is active. All other power rails are shut-down. This mode consumes very little power.
TPS65217B will be active and ready for orders in March. There is no planned end for this IC.
Thanks Stephen, I appreciate the fast responses.
Good Method, thanks a lot. I am also searching the way to let RTC running when line power is off.
Hi, Do you solve this problem?
The RTC is powered by LDO1. LDO1 remains on always as long as any power is supplied (AC or BAT or USB). If power is connected to any of the TPS65217x power inputs (AC, BAT, USB), LDO1 will remain on.
Hi. The TPS65217 is powered by battery,but the LDO1 output is still 0V.
I use the beaglebone A5 to do the experiment.
LDO1 will be always-on after the initial turn on. Even if PWR_EN goes low. However, the initial turn on (PWR_EN high) has to occur when the device goes from an unpowered condition to powered. After that initial turn on, LDO1 is always-on.
Please see the state diagram on page 17 of the datasheet for clarification. When in the OFF state, LDO1 is off. When in the SLEEP state, LDO1 is on.
the same question below,
http://e2e.ti.com/support/dsp/sitara_arm174_microprocessors/f/791/p/185846/683698.aspx#683698
maybe we can use only TPS65910 or external RTC IC like BQ32000.
Liu,
If you are referring to the errata Advisory 1.0.5 regarding the RTC, this will be fixed on the processor. The PMU operates as intended. The next revision of the processor will allow RTC only mode.
Stephen，
If we put coin cell in TPS65217B's BAT input, I think the coin cell can last only several hours, isn't it?
I think a lithium coin cell battery has a nominal voltage of 3V. So, you could not run a 3.3V LDO or buck converter with this sort of a battery. It would only be used for the RTC LDO.
You could use a coin cell to keep the RTC alive while the PMIC is in SLEEP mode.