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TPS65217 - hot swap behavior in the AC input

Rodrigo Aznar Mendes
Prodigy 215 points
Other Parts Discussed in Thread: TPS65217


We are going to use TPS65217B as PMIC in a AM335X based design.
The AC input of TPS65217B will be taken from a backplane 5V line that in general supply other hardware cards as well.

I have seen some registers default values:
   POWER PATH CONTROL REGISTER (PPATH)
      IAC[1:0]: 11 (2500mA as AC input current limit)
      
  CHARGER CONFIGURATION REGISTER 3    
      ICHRG[1:0]: 10 (500mA as Charge current setting)

  Also the default condition is the charging enabled right at power up.

We are going to use the BAT output to charge a super cap and by the default conditions above it will be charged
 right upon start up and together with the whole hardware.


- Is TPS65217B by itself able to behave in a hotswap way in the AC input?
- Which is the current curve of the AC input in this scenario?
 
  Consider scenarios of insertion of the TPS65217B hardware card or simply a general power up.

Thanks a lot,

Rodrigo

  • 0
    TI__Expert 4525 points

    Hi Rodrigo,

    yes, you can hotswap between the input supplies.  If AC is removed, TPS65217 will automatically start running off of your supercap.  When AC is re-applied, TPS65217 will automatically switch back to AC power.  It will continue running even if the input supplies are hotswapped.

    Are you asking about inrush current?  There will be some amount of inrush current when AC is inserted.  The SYS node capacitors have to charge up to 5V when AC is inserted.

    The battery charger should work fine with a supercap.  You'll need to make sure the TS (battery temp sense) pin is at a proper voltage to allow charging.  If the supercap does not have a temperature sensor, you can simply put a 10k resistor from TS to GND.

  • 0 in reply to Stephen Nortman
    Prodigy 215 points

    Hi Stephen,

    Actually I am concerned about inrush current at the moment our board with the TPS65217 is inserted in a backplane (which provides the 5V line). The same backplane should supply other hardware cards. Then the question is whether  TPS65217 has some inrush current limitation at the moment it is powered up so that the 5V main power supply is not affected.  Keep in  mind at start up the  TPS65217 will have to charge the super cap and at the same time start all the peripherals, AM335X included.

    In case  TPS65217 has some current limitation care at start up, is there any current over the time graphic ?

    Thank you very much

    Rodrigo

  • 0 in reply to Rodrigo Aznar Mendes
    TI__Expert 4525 points

    Does your customer have a specific inrush current spec that they would like to meet?

    Most likely, for your application, the two largest inrush events will be:

    --charge SYS node up to 5V

    --charge super-cap

  • 0 in reply to Stephen Nortman
    Prodigy 215 points

    Hi Stephen,

    Our project is a redesign of an automation controller.  The current design (in production) uses a LTC1422 (Hot swap controller which allows the board to be safely inserted and removed from a live backplane without impact the external power supply).

    The expected ramp (current x time) is 0 to 1A in 10ms (AC input). The current design ensures this with LTC1422, but fewer voltage lines are needed.

    Does TPS65217 current limitation ensure such behavior at AC input ?

    Thanks

    Rodrigo

  • 0 in reply to Rodrigo Aznar Mendes
    TI__Expert 4525 points

    The only time you may see inrush current >1A is when charging the SYS node (due to the high capacitance on this node).  This inrush will only last on the order of 100us.

  • 0 in reply to Rodrigo Aznar Mendes
    Prodigy 45 points

    Hi Rodrigo, I aggre with you I have the same problem, do you know what's the origen of this behavior of the TPS65217 when use a supercapacitor and switch off the source AC, sometime my system is hotswap too.

    If I use only the beaglebone I don't have this behavior, but I use my capes PCB on beaglebone and switch off the AC source my system is hotswap.

    Answer me if you have any solution. Thank you in advance.