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[TPS65950] Battery BACKUP state indication missing, and WinCE handler missing

M.A.M
Expert 8455 points
Other Parts Discussed in Thread: TPS65950, OMAP3530

 

Hi,

A customer using our OMAP3530 EVM with TPS65950 onboard, found that the battery backup mechanism is not working well. Evidently the backup status register has not the right value when booting after going to BACKUP state.

- Ideas? Please advice. Thanks.

/Magnus

First questions:

Taken from SWCA025 chapter 4:
Power cut means a momentary disconnect of the main battery (for example, when the phone is dropped
and the main battery is removed momentarily). In such a case, the capacitors connected to the main
battery can keep the TPS65950 in ACTIVE state for some time, depending on the load on the application
processor.
To support this feature, perform the following minimum steps:
1. Unmask the MBCHG interrupt of the TPS65950 power subchip by setting the PWR_IMR1 MBCHG bit to 0
2. The MBCHG interrupt is generated when VBAT falls below 3.0 V or rises above 3.2 V. Configure the
MBCHG interrupt to be generated for both of these cases by setting the MBCHG_FALLING and
MBCHG_RISING bits of the PWR_EDR2 register to 1.
If power is cut and if 2.7 V < VBAT < 3.0 V, the host processor receives the MBCHG interrupt. The host
processor must take necessary action (save data, shut down applications, etc.). If the main battery is
connected before the VBAT capacitors discharge below 2.7 V, the TPS65950 remains in ACTIVE state. If
the VBAT level increases to more than 3.2 V, the same MBCHG interrupt is recognized by the host
processor.
If the main battery remains disconnected for a longer period and the capacitors on the VBAT are
discharged below 2.7 V, the TPS65950 enters BACKUP or NO SUPPLY state (assuming VBAT < 2.1 V
and VBACKUP < 1.8 V). 
 
We has followed the above description, but has not seen the chip indicate it has been in BACKUP state.
  • How long time does it take the TSP65950 to enter BACKUP state ?
  • Is MBCHG interrupt nessary for the TPS65950 to enter BACKUP state? 

My response:

I do not see from documentation that enabling or not the MainBattery alert interrupt MBCHG to the CPU (when VBAT falling below 3.0V) , would affect the chip going from ACTIVE or SLEEP state to BACKUP state (when VBAT falls below 2.7V).
- The time it takes should be instantaneous at 2.7V, but the slope 3.0V to 2.7V depend on your capacitors. 
If the VBAT rises above 2.85V the state changes to WAIT-ON, and usually some reset would invoke the system
 
Could you describe how you expect the "chip indicate" that it went to backup mode?  (Register bit STS_BOOT BACKUP?)
I read from Section 2 in the appsnote that it is usually at boot-time when you detect this?

Second questions:

"When I cut the power, and wait some time, then power up again,  I find:
 
Register bit STS_BOOT BACKUP is always zero and the RTC is not running.
BACKUP_REG_(A..H) is always zero.
SECURED_REG_(A..U) has sometimes the values I put into them, sometimes zero.
 
We have testet the RTC on the linux, that the EVM board has on board at delivery, and found the RTC is not running when power is removed.
 
The WinCE BSP to the EVM board (rev G) does not switch on the charger for the backup battery, I have done that and the voltage is now 2V9.
I have scaned the BSP code and found no reference to STS_BOOT,
to me this indicates that the BSP is not finished on this subject. What else is missing?
 
I have put my "detector" in the RTC startup code, it is run when Windows is starting, prior to this the XLDR bootloader and the EBOOT bootloader
has run, in the bootloaders I have not found any code accessing RTC or BACKUP registers.
What do I miss?"

/Magnus

  • 0
    Intellectual 370 points

    Hi Magnus,

     

    Please find below the answers to your queries:

    How long time does it take the TSP65950 to enter BACKUP state ?

    --->  Transition to BACKUP state is instantaneous when the VBAT falls below 2.7V .

    Is MBCHG interrupt nessary for the TPS65950 to enter BACKUP state?

    ---> MBCHG interrupt is not required to enter the BACKUP state.

     

    Can you please check the register CFG_P123_TRANSITION[6] (MSK_MBLO) this bit can mask the VBATmin low threshold. (This bit should be '0' to enter into BACKUP STATE).

     

    Regards

    Ankit

     

  • 0 in reply to Ankit Somani15962
    TI__Expert 8455 points

    Case closed after some HW findings on the EVM:

    "CFG_P123_Transition, bit 6 is zero .

     Yesterday the problem disappeared, it took me som time to find what had changed:
    Normaly I switched the power off by setting the switch SW2 in the center position.  Now I removed the external power cable at the connector DC_IN.
     
    In the hardware manual for the EVM board, it says that the SW2 is a two position switch, but on the board is
    a three positon switch. That made me think that center position was off, --- I was wrong. When I studied the diagram,
    I found that some part of the circut still has power. Why the TSP65950 gets confused I don't know, maybe because of back-sourcing .   
     
    I will now modify the board so I get a real power switch. It is too slow to fumble with the power cable."
    Cheers,
    /Magnus
  • 0 in reply to M.A.M
    Prodigy 30 points
    Thanks man it really helped me. i was stuck on it for a week and did every thing i could.
    who knew this would help some one after SIX year huh.
    thanks i mean it really helped.