TPS65217B Powering AM3359

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?

Thanks,

Ali

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.

The TPS65217B datasheet says minimum voltage for BAT pin is 2.75V.  If a coin cell 3V battery is connected does this mean the device will only be able to run the battery down to 2.75V for the RTC LDO1 1.8V? 

Isleep current is 80uA typical. There is a separate spec on LDO1 IqSleep for 5uA.  Have there been measurements for current draw using a battery on the TPS65217B to only to backup the RTC power for the AM335X?  AM335X RTC current spec is around 44uA from power spreadsheet.  What is the expected current draw for a 3V battery TPS65217B and AM335X RTC?

Does the AM3335X have to do something to get the PMIC to go into the correct mode?  If the main power is removed will the TPS65217B seamlessly switch over to the battery and only power the RTC LDO1?

Thanks

Pietro,

TPS65217B does not support 3V batteries, as the UVLO is set to 3.3V.  The device will seamlessly switch between inputs as they are applied/removed.  As for moving into Sleep mode, please see the datasheet:

"To enter SLEEP state, set the OFF bit in the STATUS register to ‘0’ (default) and then pull the PWR_EN pin low. All power rails controlled by the power-down sequencer will be shut down and after 1s the device enters SLEEP state. If LDO1 was enabled in ACTIVE state, it will remain enabled in SLEEP sate. All rails not controlled by the power-down sequencer will also maintain state. The battery charger will remain active for as long as either USB or AC supply is connected to the device. Please note that all register values are reset as the device enters in SLEEP state, including charger parameters." 

So if we want to have the coin-cell battery used to backup the RTC during power-fail, an autoswitch such as the TPS2115 or TPS2101 would have to be used, and then, is the BAT IN on the TPS65217 simply left NC? 

-Leonard

Use an external LDO to supply the RTC.  Connect the coin cell battery to the external LDO.

That would imply the coin cell is always powering the RTC.  I want the coin cell for the RTC only if there is a power-fail, otherwise, RTC is powered from the 1.8v bus.

put a diode-or at the input of the external LDO

This is the configuration we generally recommend for always on RTC operation with a coin cell:

BAT pins can be left floating.  Page 36 of the datasheet details battery-less operation.

Which diode part number does your diagram refer to?  It only mentions 100mV drop across the diode.  Reverse leakage spec is also important so current does not flow into the Lithium Coin cell (not a rechargeable battery).  Please provide part number for diode. 

The reason why TPS2115 or TPS2101 was suggested instead of the two diodes was to try to reduce the voltage drop that a Diode-Or topology has.  Do you believe this would be the case?  I would like to try to maximize the coin cell battery life.

Thanks