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TPS2553: The behavior of current limit

Dice-K
Mastermind 7500 points
Part Number: TPS2553

Hello,
I have two questions about TPS2553DBV.

My customer is checking the operation by the mounting to a prototype.
Please give me comment about the following behavior.

■The condition of TPS259231
IN-pin : 5.0V input from external power supply
ILIM-pin : 47kohm (current limit setting is 557mA(typ))
OUT-pin : Load electric current adjustment by the electronic load connection
  OUT line has capacitors of 141uF(47uF*3).

(1)
The data-sheet describes as drooping characteristic that keeps the current limit value when we increase the load.
However, the measurement data of my customer is the characteristic of 'フ' after around 3V as follows.


※For USB-DCP movement, he wants to maintain a limit electric current to 2V.
  Please teach him the way of keeping drooping characteristic.


(2)
About the waveform of output voltage and output current.
The range of drooping characteristic: Output voltage is 3.5V.
(Ch1: Output voltage,  Ch4: Output current)
It is the expected output without oscillations.

However, the range of the characteristic of 'フ': Output voltage is 2.5V.
(Ch1: Output voltage,  Ch4: Output current)
Output voltage and output current have cyclic behavior.
There are overshoots, too.

※Please teach him the reason about these behavior.

Regards,
Dice-K

  • 0
    TI__Mastermind 42795 points

    The behavior observed may be related to the use of an electronic load. If possible, retry using a resistive load (maybe use a decade box or some other variable power resistor). The E-Load may not be able to regulate current (CC mode) when the output voltage goes below the spec of the E-Load.

    For the oscillation, at first it appeared to be thermal cycling (TPS2553 has built in thermal shutdown) but the output voltage is not going to ground (power switch turns off) when the current goes to zero. Make sure your input supply is not oscillating or drooping and causing the measurement above.