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TPS65217: Spike of BATT pin

Guru 12130 points

Part Number: TPS65217

Hi,

Does the spike of the BAT pin as follows affect AC detection?

This spike is around 4V peak.

Best Regards,

Kuramochi

  • Kuramochi-san,

    Thanks for the post! Can you provide some more details on when this occurs?

    Regards,

    Paul Kundmueller
  • Guru 12130 points

    In reply to Paul Kundmueller:

    Paul-san,

    On shutdown, SYS is connected to BAT.
    I think the connection is made exactly when SYS is dropping from 5V to it's OFF state voltage level.
    So, the spike we are seeing is the drop of the SYS voltage.

    Best Regards,
    Kuramochi
  • In reply to TQ:

    Kuramochi,
    The deglitch time for power path is 22ms. From the scope shot, it looks like the spike is less than 1ms so it should not effect AC detection.
    Thanks,
    Jay
  • In reply to Jayanth Kruttiventi:

    Hi Jay,

    Datasheet says that 22ms power path deglitch is for voltage increasing? Does this mean that the deglitch only applies to voltage detection and not voltage REMOVAL detection?

    I may be understanding this wrong.

    Regards,

    Jesse

  • In reply to Jesse Caparangca:

    And could it be in someway related to this statement  from the datasheet:

    9.3.9.1 Shorted or Absent Battery

  • In reply to Jayanth Kruttiventi:

    Hi Jay,
    Any thoughts about the voltage removal detection deglitch?
    Thanks,
    Jesse
  • In reply to Jesse Caparangca:

    Jesse,

    Can you confirm the time scale in the initial scope shot shared in the thread? Is it 5ms/div as it appears in the lower-right hand corner?

    Can you provide a scope shot showing VBAT, SYS, and AC all on the same plot?

    Thanks,

    Brian

  • In reply to Brian Berner:

    Jesse,

    I would also be interested to know the value of Register 0x04 (CHGCONFIG1), bit D0 (CHG_EN) used in your system.

    The default/reset value of this bit is '1', but you mentioned that there is no Battery in your system. In the absence of a battery, there may be measures we can take be writing values in the Register Map that will prevent your glitch on VBAT.

    There is a whole section in the TPS65217 datasheet's Application section titled "10.2.2.2 Battery-Less/5-V Operation" (pages 75-76). Does your system match Case 1/2 or 3 more closely? How is your TS pin terminated? 

    Please refer to this section and verify your schematic is connected as shown in Figure 56 and read through the functional differences in the first column of Table 36, titled "POWER SUPPLIED THROUGH AC PIN"

  • In reply to Brian Berner:

    Hi Brian,

    Yes, the timescale is indeed 5ms/div in the first image.

    Here's a scope shot of the AC, SYS, and BAT pin.  For this image I had to disable the AC power path to perform a shutdown. The only board I have available for scoping has a damaged RTC section so shutdown by ALARM2 is unavailable. BAT pin behavior and other symptoms are similar though. 

     (Pink-AC; LightBlue-SYS; DarkBlue-BAT)

    CHG_EN bit is left at its default enabled value (1). We've scoped and tried disabling this register before and still saw the same spike, although we did not study the differences in detail. The spike may be occurring a couple microseconds later or something like that.  I think the spike will be there regardless of the charger settings. The spike we're seeing is when SYS is connected to BAT during shutdown and therefore following it all the way to its steady state.

    We have our circuit configured similar to case 1/2 of section 10.2.2.2. Only difference I see is we don't have BAT and BAT_SENSE shorted to each other - all three are floating. TS is also left floating just as the left configuration in figure 56.

    Regards,

    Jesse

  • In reply to Jesse Caparangca:

    Jesse,

    This is expected behavior. BAT is the primary supply to SYS and AC/USB is the secondary supply.

    When the shutdown occurs, SYS is connected to BAT (entering the original power path state), and you are seeing the voltage at SYS appear at the BAT pin while SYS discharges.

    Is this behavior causing a problem in your system?
    Or are you simply observing this odd-looking behavior and asking to verify that it is normal?