• State TI Thinks Resolved
  • Locked Locked
  • Replies 4 replies
  • Answers 1 answer
  • Subscribers 64 subscribers
  • Views 743 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.

TPS2115A: TPS2115A inrush current issue

Lina Wang
Intellectual 960 points
Part Number: TPS2115A
Other Parts Discussed in Thread: TPS2113A,

hi  sir,

two question as below:

1.our customer have two power supplier application, in the auto switch mode, they test condition if IN=IN2, Voltage is less then 4V, out put voltage is only 2.95V, without 150UF cap when come inrush current (1.17A).

if add one 150uF in loading, system can work, otherwise 2.95V output have been trace to their GSM Shut down voltage.n if they adjust input voltage to 3.9V , output need two 150uF to support system work.

and if they input down to 3.7V, CL need 10pcs 150uF to support system work. 

input voltage IN1/IN2

CL CAP Request

4.1V

0 PCS 150UF

4V

1PCS150UF

3.9V

2 PCS150UF

3.8V

7PCS 150UF

3.7V

10 PCS150UF

we know  spec show "High inrush currents can glitch the voltage bus and cause a system to hang up or reset." so above is normal, right? but we this inrush current is only 1.17A, haven't up to 2A current limit.

how to do can reduce this higher drop out without so many 150uf CAP.

2. p16 Spec is show a circuit that will connect IN1 to OUT until the voltage at IN1 falls below a user-specified value, what's mean  is "user-specified value", is it can be set by customer, or is fixed value.

  • 0
    TI__Genius 15740 points

    Hi Lina,

    Is the waveform you attached a result of switching the input every few milliseconds, or is this with the device set to turn on the highest voltage supply? Also, did you say that both IN1 and IN2 are the same voltage in your application? If this is the case, then perhaps the waveform you are seeing is a result of the device switching back and forth between the two channels. The inrush current may be pulling down the supply voltage on IN1, and as a result IN2 (no load) is now higher. The device will then switch to IN2 but the current on IN1 is gone so IN1 rises and IN2 drops. Then the device will try to switch back in IN1, and this will cause a cycle similar to what you have shown in the scope shot.

    Can you please let me know how the device logic is configured and how you are measuring voltage drop across the device? Do you have any scope shots showing IN1 to IN2 transition? When is the 2.95V output seen in the application?

    Thanks,

    Alek Kaknevicius

  • 0 in reply to Aleksandras_Kaknevicius
    Intellectual 960 points

    HI Alek,

    You seems omit my second question as below 

    ---p16 of Spec is show a circuit that will connect IN1 to OUT until the voltage at IN1 falls below a user-specified value, what's mean  is "user-specified value", is it can be set by customer, or is fixed value, how to use these "user-specified value"?

    And about above my first question, about voltage drop across the device, customer measured as below output loading wave, it is IN1=IN2 is 3.65V battery, and output voltage is 2.95V, with 10pcs 150UF CL.

    and customer haven't any scope shots showing IN1 to IN2 transition, it need use the two scope to trace two supplier current, if you also need it, customer will add it next time.

    note: their loading is GSM device, so there is inrush current when transmit, 

  • 0 in reply to Lina Wang
    Intellectual 960 points

    hi Alek

    add device configure is as below schematic,D0 and D1 as below configure.

    :

  • 0 in reply to Lina Wang
    TI__Genius 15740 points

    Hi Lina,

    Let me address your question below:

    ---p16 of Spec is show a circuit that will connect IN1 to OUT until the voltage at IN1 falls below a user-specified value, what's mean  is "user-specified value", is it can be set by customer, or is fixed value, how to use these "user-specified value"?

    This is a typo in the datasheet. The TPS2113A is a different device where one of the pins can be used to set a "user-specified value" for switchover. The TPS2115A does not have this functionality.

    I see in the schematic that D0 is labelled as "NC". Does this mean it is left floating? If so, then it will be pulled up, and the device will select the higher of the two input supplies. Since both are the same value, the current loading of the output may cause the input to drop. This means the other input may have a higher voltage during these conditions, so the device will select the other input instead.

    You may want to take a look at the TPS2113A. If you did want to set a "user-specified" value for switchover, then this device would be the better choice, especially with equal voltages.

    Thanks,

    Alek Kaknevicius