• State Resolved
  • Locked Locked
  • Replies 10 replies
  • Answers 3 answers
  • Subscribers 63 subscribers
  • Views 178 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

TPS2124: SEL Pin Floating

KrnB
Intellectual 580 points
Part Number: TPS2124
Other Parts Discussed in Thread: TPS2120, TPS2121,

Tool/software:

Hello, 

Is there an internal pull down/ pull up on SEL pin ? This is to confirm if SEL pin can be left floating.

In the datasheet Figure 16, the delay in switchover after SEL Pin is ~2ms. Why such delay after SEL pin change ?

  • +1
    TI__Mastermind 20260 points

    Hi KrnB,

    SEL can't be left floating as it doesn't have any internal pullup/pulldown resistors.

    TPS2120 and TPS2124 have a slight delay when switching from IN2 to IN1 (not from IN1 to IN2), but TPS2121 does not - if you need a fast response time switching to both IN1 and IN2 I recommend using TPS2121 and toggling the CP2 pin.

    Thanks,

    Patrick

  • 0 in reply to Patrick Shalton
    Intellectual 580 points

    Thanks for the reply. 

    In the datasheet Figure15, the total time to move from IN1 to In2 is 365us which is cumulative of switchover time (tsw = 100us) & Slew Rate control time.

    I am unable to figure out the Slew Rate time. Please can you help to calculate the slew rate control time.

  • 0 in reply to KrnB
    TI__Mastermind 20260 points

    Hi KrnB,

    The falling slew rate depends on the load capacitance and resistance. If IN1 is higher than IN2 (or vise versa) after the switchover is initiated, IN1 disconnects from the output, the output capacitors discharge to the IN2 voltage through the load resistance, then when VOUT = IN2, the 100us switchover takes place where IN2 is connected to the output.

    Thanks,

    Patrick

  • 0 in reply to Patrick Shalton
    Intellectual 580 points

    Does this mean that Slew Rate control (defined by Css)  is only applicable when the Mux Output moves from lower voltage to higher voltage?

  • 0 in reply to KrnB
    Intellectual 580 points

    Hello Patrick,

    Please can you help me understand more on Slew Rate control in TPS2124. 

    I see your reply that falling slew rate depends on the load capacitance and resistance. Does that mean that hat Slew Rate control (defined by Css)  is only applicable when the Mux Output moves from lower voltage to higher voltage?

  • 0 in reply to KrnB
    TI__Mastermind 20260 points

    Hi KrnB,

    The slew rate control is used for each input only once after the input becomes valid - please see below. During subsequent switchovers, the inputs are immediately connected.

    Does this help?

    Thanks,

    Patrick

  • 0 in reply to Patrick Shalton
    Intellectual 580 points

    Hello Patrick,

    Thank you for the reply. 

    Is there a formula to calculate the Output Slew Rate during initial starting or switchover?

    My understanding is that Figure 3 from Datasheet for Output Slew Rate is just an estimate & cannot be respected always due to application specific variables like Output Bulk Cap, Load Current & difference between voltage level. Is this correct?

    Regards

    Karan

  • 0 in reply to KrnB
    TI__Mastermind 20260 points

    Hi Karan,

    There's no formula published in the data sheet for output slew rate during soft start. Yes, for this device the output slew rate is an estimate with data points in Table 7-1. The main affecting factors are VIN and CSS - that's correct.

    Thanks,

    Patrick

  • 0 in reply to Patrick Shalton
    Intellectual 580 points

    Thank you, Patrick

    I will refer Table 7-1 for Slew rate estimation.

    In my application, I am worried about the maximum voltage droop on Output Bulk Cap during switchover.

    My understanding is that the Slew Rate of the Output does not affect the voltage droop on Output Bulk Cap during switchover. Please confirm if my understanding is correct?

  • +1 in reply to KrnB
    TI__Mastermind 20260 points

    Hi Karan,

    That is correct, the time when neither input is connected, which is when the output droop takes place, is fixed at 100us typ regardless of slew rate programming.

    Thanks,

    Patrick