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TPS65950 + OMAP35x charging a discharged Li-Pol battery

Pev
Prodigy 245 points
Other Parts Discussed in Thread: OMAP3503, TPS65950

Hi All,

We're working on a design based on OMAP3503 + TPS65950. While our hardware is in production, I've been looking at power management and battery charging on the Rev D Mistral OMAP35x EVM. We've done a few mods to the board to bring it in-line with the reference design in 8-1(B) in the TPS65950 TRM :

  • Linked VBAT_IN to J4 pin 2 to bypass load-switches.
  • Removed Q5 and R164

We've also changed R99 to 150K to enable BCIAUTO.

This configuration appears to charge and discharge with a battery when (approx) VBAT_RAW > 2.6v. However, if the battery discharges further and drops below 2.5v the voltage and charge current drop to 0. On plugging in the charger raises VBAT_RAW to 0.75v but no charging takes place when I'd have expected to be en the "SMALL PRECHARGE" phase from TRM figure 7-2.

Note that this is using a board set to boot from MMC with no card inserted so this should be relying on the TPS65950 hardware starting a pre-charge here. I think I'm probably missing something really obvious here as I'd expect to be able to charge a very discharged battery!

Best Wishes,

~Pev

  • 0
    TI__Genius 15100 points

    Hi Pev,

    I dont have a board to test your scenario. I asked Mistral developers to provide some help on this. Following is the response I got. Let me know if this helps:

    On Rev-D Main board we have the Load switches that selects between real battery and Pseudo battery.

    And enable signal of the load switch (Real Battery Side)  is again pulled high to the same supply (Battery), which will not be good enough to enable the load switch when the battery voltage goes down. This disconnects battery path from TPS65950. In the latest version of EVMs have these switches removed.

    I would suggest then try shorting VBAT_IN (J11-1) and VBAT_RAW (R177- any pad) – for this experiment ONLY.  Make sure Power switch is Battery only position.

    Caution Note: With this modification, flipping the power switch to Pseudo Battery might spoil the battery / some components in EVM.

    If you are using a AC charger then yes, the device is capable of charging a very discharged battery.

     

    Regards,

    Gandhar.