TPS65910 start up without pushing the button

Hi Flore,

Unfortunately, what you are describing will not work.  I know this is an old post but my colleague and I tried this exact scenario about a year ago and it does not work.

The issue is (pg.33 of the datasheet) that PWON must be released from ground or the PMIC (using AM3505) will not turn 'ON'.  That is why the EVM documentation has the pushbutton switch in the schematic.  I have found out the HARD WAY that this part is really intended to be used with a pushbutton switch.  This is the only way you can guarantee an initial state for the PMIC's state machine.  We are using this PMIC without a pushbutton and I have ultraCAPs on the power inputs.  I have had to design special circuitry to disconnect the ultraCAPs from the PMICs power inputs and I still occasionally have issues with the PMIC not coming back 'ON' after a shutdown. 

I'm surprised more customers are not having this issue perhaps they are using the pushbutton switch.

Hi Davey,

The problem has been solved.

Use a RC delay on PWRON pin. At the beginning of powerup, PWRON pin keeps low due to the capacitor, and the capacitor is charged via a resistor. at the end, the PWRON pin is high.

This solution has been verified by local FAE.

Hi Jerry!

Could you please provide me with value of R and C. Is it, for exapmle, correct values C=1uF/R=10K

Thanks,

Vasiliy

Might be usefull:

I test this nominals and it works:

R = 510K (0402)

C = 10uF (0805)

Tested on AM335x Development Kit (i replaced R112 to 510K, and soldered C=10uF between pins 2,4 of SW5), now DevKit starts without pushing of button.

Thanks,

V

Hello,

I don't understand why the R/C circuit is necessary in order have the unit power on without a push button.  Could we not just simply connect PWRHOLD to VRRTC output specifying the device should turn on and stay on whenever power is applied?  and then just leave PWRON as not connected.

This method is used in the Crane board:

http://designsomething.org/craneboard/w/hardware/default.aspx

Jarrod,

I think the crane board works because the pwrhold comes from the VRTC and this allows the internal logic of the PMIC to acomplish a sucessful POR.

I have tried the 5V to pwrhold and bad things happen to the AM335x-SK, pretty much the processor must have rail sequenceing wrong and it fails, it also only fails after some amount of power cycling not initally.

Thanks for the link to the craneboard.

Hmmm, interesting.  So since they are using VRTC it essentially means that PWRHOLD is always held high (unless the backup battery dies).  So even when the device is unplugged PWRHOLD is high.

I have some prototypes of a custom board i am going to play with the different ways and see what happens.  I did put pads on the board for the RC circuit if the other ways fail or I am to afraid to use them since you say the failures occur after an amount of power cycling.

I'll post back what i find.

Hi,

We also have same doubt about the PWRHOLD and PWRON pins of TPS65910AA1.
In our customer board the TPS65910AA1 is not working at all (so AM3352 is not working).
There is no output from the TPS65910.

We have connected PWRHOLD to an external 3.3V power to keep it High
and as we don't need the push button, PWRON pin is left floating similar to the crane board.

Below are the results of few test points after applying power to TPS65910.

INT1 -> 0V
SLEEP -> 0V
PWRON -> 5V
BOOT0 -> 0V
BOOT1 -> 1V
PWRHOLD -> 3.3V

Please let me know what else should be tested to analyse the problem
and is it ok to leave PWRON pin floating if the push button is not necessary.

Regards
Prad

I ended up pulling the PWRHOLD Pin high and then just putting some pads on my board for the RC Circuit just in case, but i never needed them because pulling the PWRHOLD pin worked fine for me.  Here is my setup in case it helps (this is currently working for me):

The only input voltage is the +5V, the rest are all output voltages.  As you can see R21 and C97 are Non-populated meaning my PWRON pin is floating like yours.  I am using the A3A1 as i have DDR3, but other than that it sounds like we did the same things.  Hope the image helps, Good Luck!!!

Thanks for the sharing you setup Jarod.

One more thing I would like to highlight here for Prad1 setup that boot 1 should be connected to 1.8v to VRTC.

Hi Jarrod,

Thank you so much for the details.Very helpful information.

Hi Puneet,

Thank you,

Regarding BOOT1 we have connected to VRTC pin of the TPS65910A,
but after applying power the output voltage of VRTC is around 1V.

I have posted the schematics in the below post and we believe
there is no mistakes in the circuit, but accoring to the test points,
we believe there is something wrong in the device.

http://e2e.ti.com/support/arm/sitara_arm/f/791/p/320847/1116496.aspx#1116496

The only outputs we are getting is 1V at VRTC pin and VAUX2 pin.
and the PWRON pin is 5V, so it seems some part of the device is working
but we are not able to conclude if the device is Dead in order replace it
with a new one.

Could you please let me know if there is any way(Test pins) to
conclude the device is dead?

Regards.
Prad

I see on your schematic that you had PWRHOLD connected to VAUX33 which will not work, but also see that you later connected it to and EXTERNAL 3.3V supply.

Have you tried connecting your PWRHOLD pin directly to the 5V VCC power input to the part?  There is an internal pull-down on that pin enabled by default so just connect it directly to the 5V.

Please check NRESPWRON pin if it goes to 1.8v or not. If not device didnt power up. I looked at your schematic nothing seems that will stop the device to boot up.

VRTC has to go to 1.8v , if not then PMIC will not function. How much is the current consumption on PMIC? Before you debug anythnig else this has to be resolved.

May be try to replace the PMIC.

Hi Jarrod, Puneet

Thank you so much for checking the schematics.
We shall try your suggestions and also replace the IC with new one
and come back with the results.

Regards
Prad

Hi Jarrod, Puneet

One confirmation about the PWRHOLD pin connection.
The TPS65910Ax datasheet mentions that PWRHOLD pin could be connected to
VDDIO/VCC7 supply, but according to this below post,  Puneet has recommended to
connect to 3.3V(as per the VDDIO).
http://e2e.ti.com/support/arm/sitara_arm/f/791/t/250006.aspx

Since we are using VDDIO at 3.3V, should we connect to 3.3V?
currently we are trying to connect 5V.

Regards
Prad

The range on that pin is 1.65-5.5V, so connecting to 5V is fine.  Since you are using PWRHOLD to turn the device on you cannot connect to VAUX33 because this domain is not powered in the device OFF state. 

You need to either connect it to VRTC which will be powered even in the device off state, or directly to your supply (VCC7).  I chose to just connect it directly to VCC7 and everything is working well for me.

In the post you mentioned they are referring to the starter kit which makes use of the PWRON signal and in that setup the PWRON signal turns the device on at which point VAUX33 will turn on and pull up the PWRHOLD signal keeping the device on.  Since you are not using a power-on button then this setup cannot work for you.

Thank you for the details.

Andreas,

I had moved to a TPS65217 for the AM3358 device, I belive this powers on with change in AC power input or USB this allowed u-boot to boot then write to the internal PMICs PWRHOLD register.

I have also used a TPS65037 this required the reset_in pin to be tied to the power good signal as when the 3.3 dropped this triggers power down sequence.
This should be done for the input of the TPS65217 if there is no back up supply.

I don't know If this answers you question, just be sure to check the power down sequence is done to ensure the processors are not damaged.

-Josh

Josh,

thank you for your reply. Your answer brings up another question. You mention the power down sequence. This may be a problem for us.

We use the PCB with the AM3356 in a bigger maschine for display control. The board is powered by 24VDC and via DC/DC-Converter with 5VDC. If the maschine is switched off the 24V is switched off immediatly.

Could the TPS65910 run his power down sequence in this case? Do you have any experiance in this?

What is about the "Discharge resistor for power-down sequence RDIS", mentioned in the datasheet at page 20 last row. Is this an internal resistor?

Thanks for your support

Andreas