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TPS2554EVM-010: IOS doesn't keep at the limit value

Pearl Lin
Prodigy 310 points
Part Number: TPS2554EVM-010
Other Parts Discussed in Thread: TPS2554

Hi Engineers,

My customer test our EVM and have problems on the condition of Over current situation.

test comdition:

  1. Power supply : 5V/10.3A

  2. electric power load : CC Mode and sink to 1.25A(Ilimit =1.2A) .

Q1, as below Vout waveform, when the Iout>1.2, the Vout seems like auto retry, but customer would like not only the Iout clamp at 1.2A but Vout also clamp at 5V for usb, could TPS2554 to do that? or what's the right part to do this function?

 

Q2, Setting current limit at 1.2A , but the current output seems not clamp at 1.2A when sinking 1.25A from Electrical load, what may be the reason? please see below two figure.

(sink 1A,with 5V Vout)

(sink1.25A, 0Vout, but it literally need to be clamp at 1.2A)


looking for your quick reply, thank you.

  • 0
    TI__Expert 3135 points

    Hi Pearl，

    A1：do the customer want the vout keep 5V, Iout keep 1.2A(limited current) when the sink current is bigger than 1.2A ? for our power switch, we can't control the front power supply, so when sink current is bigger than limited point, we just can control the on/off of the switch(thermal cycle). if customer  want the vout keep 5V, Iout keep 1.2A(limited current), they should consider the Integration solutions(Integrated power supply and current limiting switch), if their application is for USB, TPS25830 is a suitable part for them.

    A2: As I said above, our switch cannot keep the current  at 1.2A. If the current exceed limit point, TPS2554 will enter a cycle state. We can use an oscilloscope to see whether current point is 1.2A，when TPS2554 entered the cycle state.

    if you have any other further question, please feel free to contact me.

    Regards,

    Kevin

  • 0 in reply to Kevin-Cheng
    TI__Prodigy 310 points

    the part you recommend TPS25830 Q1 is over-killed to the customer, though their system is as below.

    -the PDA need 5V/2.5A when there is no battery on the cradle.

    -the PDA need 5V/1.5A when there is battery parallel on the cradle, battery needs 1A.

    -Customer are not sure if the end customer’s PDA will decrease the charging current to 1.5 A automatically when battery is parallel with PDA,

    So they need a current limit which could active clamp the current and voltage even on the over current condition.

    -We choose TPS2554 for HW control, two limit setting and select pin.

     

    The would like the solution with HW control only, except TPS25830, do you have other recommendation?

    I have sent you some block diagram from mail, please check, thank you for the quick reply.

  • 0 in reply to Pearl Lin
    TI__Expert 3135 points

    Hi Pearl,

    First,the TPS2554 can’t keep 5V when the current is bigger than the current limit point, but TPS2554 can ensure that the output current is constant at light overcurrent, but the output voltage will drop accordingly. For the light overcurrent performance, please refer below pictures. the current performance is like figure2 and figure3 on datasheet is right.

    In addition, the reason why the current can’t keep 1.2A when customer draw 1.25A is that customer use the Electrical load, if they use pure resistance, TPS2554 can keep 1.2A output current. The Electronic loads can’t maintain the characteristics of a normal load when overcurrent occurs.

    Best Regards,
    Kevin