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TPS1641: I_ocp Current limit time response uncorrectly.

Weikang Wu
Prodigy 40 points
Part Number: TPS1641


Tool/software:

hello, dear engeenrs, I encountered this issue recently, I use TPS16413 as current limit power switch in my data collector  application. It work fine when The output of TPS16413 is connect to 1A resistive load or resistor load with 470uF ECap. But when my data collector is connected to 40 devices thas have a DCDC stepdown circuits,  the power switch don't work corretly. I've try adjust the value of C4( C_IDLY) from 1nF to 10nF, the time delay is always 1.38ms.

  • 0
    Prodigy 40 points

    PS: the ref of C5/C4 in the calculate table are reversed.

  • 0 in reply to Weikang Wu
    TI__Mastermind 34631 points

    Helo Weikang,

    You are testing for the highlighted condition. 

    During the current limiting, the device dissipates a power of (VIN – VOUT) × IOUT and the device gets heated up. If the junction temperature of device reaches thermal shutdown temperature (TTSD), the device turns off the internal FET.

    Because of TSD device latching off before TLIM_DUR

    Thanks 

    Amrit 

  • 0 in reply to Amrit Jit
    Prodigy 40 points

    I have just tested the power on condtion when I use a PMOS instead of TPS16413. Peak surge current ramp to nearly 16A in 500us and decay to 100mA in 5ms . Is there any solution or ohter part that I can apply in this condition? Power on surge is so big and stead current 1/100 to 1/10 of the peak value.

  • 0 in reply to Amrit Jit
    Prodigy 40 points

    The DCDCs of son-devices connect to data collector sink huge current during start-up. These device imply a old-style DCDC stepdown IC without soft start-up feature. Data collector must handle this situation.

  • 0 in reply to Weikang Wu
    TI__Mastermind 34631 points

    Hello Weikang,

    Is 16A inrush current or it's some surge test?

    Please clarify.

    You can use /FLT pin of TPS1641 as PGOOD pin to enable DC-DC converter. 

    I am not clear on the test case. Is the 16A coming because of PFET?

    Thanks 

    Amrit 

  • 0 in reply to Amrit Jit
    Prodigy 40 points

    I worked on 2 test cases. case 1: TPS16413 as load switch; case 2: P-MOSFET + resettable fuse as load switch. In both cases, I used the same load: 40 devices which imply a dcdc as stepdown power supply. In case 1, the current and output voltage can't ramp up because TPS16413 shutdown due to over-heat as you explained. There are 40 devices(40 devices means 40 DCDCs) connected to the output of TPS16413 with a long power cable. I can't connect FLT pin the control the EN of DCDC converter. In case 2, the current ramp to 16A in 500us because the resettable fuse is not triped in such a short time.

  • 0 in reply to Weikang Wu
    TI__Mastermind 34631 points

    Hello Weikang,

    Looks like TPS16413 is doing a good job here.

    Is your concern about TPS16413 hitting TSD? It's of no concern. Current limit works that way.

    Thanks 

    Amrit