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Original question:

TPS92692: LED driver

TPS92692: LED Short-Circuit Test

user4742059
Prodigy 120 points
Part Number: TPS92692

Hello Team,

I Have meet a problem when I test LED short-circuit on TPS92692EVM, the phenomenon is different from the waveform provided in datasheet.

channel 1 is output of IMON pin, channel 2 is SW wave, and channel3 is the FLT pin output.

When short to GND happened, as shown in below figure, a pulse up to 3.7V on IMON pin appeared and recovered soon, SW wave still exists. and FLT pin was pulled down then pulled high automatically after about 30ms.

A more detailed wave at short circuit is shown as below:

During the short to GND, the device did not hiccup with connecting the FLT pin to the SS pin, and the SW still exists, the FLT pin is high, as shown in below:

I don't know how to solve this problem.

Thanks!

  • 0
    TI__Genius 17690 points

    Hi Xiaoquing,

    Are you using the EVM in Boost or Boost to Battery mode and I assume the short is permenent short?  Can we please have your configuration of all the jumpers on the EVM?  I want to verify the the signal you lable SW is the voltage signal on the Drain of of Q3.  We would also like to have scope captures of the following signals with the scope on 50mS/div then also zoom into the FLT falling edge with 5uS/div.  We would like the votlage setting on OV signal to be 200mV/div.  Thanks

    CH1:  FLT (trigger negative edge of FLT)

    CH2:  TP3 (Output Voltage)

    CH3:  OV (pin15 on TPS92692)

    CH4:  Drain of Q3

  • 0 in reply to Tuan Tran74
    Prodigy 120 points

    The EVM is using in Boost to battery, channel 1 is FLT pin. channel2 is output voltage, channel3 is OV pin(connected with the resistor divider R5 and R11), channel4 is the SW(the Drain of of Q3).

    thanks! 

  • 0 in reply to user4742059
    TI__Genius 17690 points

    Hi Xiaoqing,

    Did you modify the board to the schematic on page 16 for Boost to Battery (Buck-Boost)? How are you shorting the output voltage to ground?  From what point on the schematic did you short to ground on page 16 of the user guide for the evaluation board? 

    If you shorted the output voltage (TP3) to ground then the short that you provide is not truely a short since the output votlage (TP3) from your scope capture is still at 18V.  If it was a short then it would have gone to 0V.

    Thanks

  • 0 in reply to Tuan Tran74
    Prodigy 120 points
    Thanks very much, I have something wrong before, when the Vout short to GND, the hiccup works
  • 0 in reply to user4742059
    TI__Genius 17690 points

    Hi Xiaoquing,

    I am glad to hear that we have resolved this.

    Thanks Tuan