Problem with POWER UP for Sitara and DDR2

Yes, I use 10uF capacitor close to Power management chip.

Removed from the board DDR chips, I test them separately of "laboratory supply"  I supply them to   3V

And I test VIO Rail from Power Management chip: I measured 1,79V to 1,81 V

VIO =  1,79V to 1,81 V      That is OK ?

then the problem is still

 VDDS_RTC of Sitara is powered from  RTC Power management Rail = 1,8V  That is problem ?

In many kits provided by Texas, I see external LDO ( TPS71718 )  for  VDDS_VRTC =1,8V.  I guess it is used in the case of larger power consumption by Sitara ?

HI Biser,

I still looking for the cause of my failure.

I noticed that in the Power Management chip : TPS65910A  VDDIO is connected by 1,8V or 3,3V  voltage Rail.

I know from the documentation that the choice of voltage depends on the power to the other bus. (I2C.....)  

But is there any possibility to have relation with VIO Rail ?  My choise for VDDIO is 3,3V.

HI,

Today, I pulled out  processor Sitara from the board.

I did measurements on the board and chip and confirm that short it comes from the Sitara.  Short gives only between  VDDS_DDR and VSS.

My question is: Is it possible short was caused by overloading due to an incorrect sequence of supplied voltage ?

No, I measured anywhere. Short is only between VIO and GND. 

I asked the above question because the PMIC and Sitara are not in the same board.

Board with Sitara stepping over the power chip through connector.  I doubt connector not making contact on one of its pins

Hi again,

I ran PMIC without CPU, by the following procedure: 

1. Power on PMIC with 5V, 

2. Connect  first pin of  PMIC  (PWRHOLD)  via an external LDO=1,8V  ( starting the release of the voltages: VDAC, VDIG2, VDIG1, VIO........ from PMIC ).

3. to VIO output , I measure the following values: sometime VIO = 1,8V , sometime VIO=5V 

each  new measurement is performed after a power rebooting of the PMIC chip.

Аny suggestions why is observed this ?

I did some tests, and appointed the following:

When I decreased  PMIC power supply (VCC7) from 5V to 3,3V .  behavior of  "VIO" Rail is normalized. i.e. each time the voltage of VIO is 1,8V.

Тhis situation comes the following question:
Is it a mistake that the supply of PMIC is 5V (VCC=5V) ?

Hi Biser

Definitely, the PMIC  does not work, at VCC7= 5V.

I feed PMIC with laboratory power supply unit. When the voltage from power supply is from 3,3V to 4,8V everything is fine.

But at the moment when I submit voltage to 5.0V   -   VIO=5.0  to 5.2V

The part number of PMIC is : TPS65910AA1RSL

I designed a system on two boards:  "Mother Board" (2 layer board), where is located the PMIC.

Аnd a second board: (6 layer board)  which stands directly above "Mother Board" .

On this board is located Sitara, DDR2 and  Flash.

Yes.

I can generally separate by three cases:

----------------------------------------------------------

I case:

When is a without " Sitara" Board" ,  and powered on 5V (VCC7=5V) - VIO Rail behave strangely:  

- > 0V  or 5V  from the start of the power supply,   or

-> 1,8V  in the beginning ,  then after a few seconds (5-6 sek.)  VIO goes to 5V. and this voltage stay for continuously.

____________________________

I I case:

When is a with "SItara Board"  and powered on 5V,

-> 1,8V  in the beginning ,  then after a few seconds (5-6 sek.)  VIO goes to 5V

-------------------------------------------------

III case:

When PMIC is powered with 3,3V - 4,8V ,  no matter whether whit "Sitara board , or not.   VIO Rail is 1,8V  and this voltage not changed.

If you ask how many boards I test. 

I perform the test on 5  Mother boards + 5 Sitara boards.  At the all is observed the same.

Yes, The PMIC is conected through tetmal pad to GND

Тhanks for the advice, :)  I continue to fight with the problem.

I suspect that may be parasitic inductance and capacitance.

When I get a answer, I will write here.

Best Regards,   and greetings to Dobri Denchev  :)