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TPS92611-Q1: Schematic review, chip broken 4pcs

Xiong JIANG
Prodigy 180 points
Part Number: TPS92611-Q1

Tool/software:

Hi Expert,

Would you please help to have a review on the schematic? Is there any mstake? We have 4pcs PCBA broken, and finally found all of them are TPS92611-Q1 broken, pin5 short to pin6 when it is unistanlled on PCBA.

2260.schematic.pptx

  • 0
    TI__Genius 10040 points

    Hi Xiong,

    What do you mean "pin5 short to pin6 when it is uninstalled on PCBA"?  and what's the damage phenomenon? please share a LED schematic with components' value.

    BR, Hailee.

  • 0 in reply to Hailee Xu
    Prodigy 180 points

    Hi Hailee,

    We remove the chip from PCBA, measure this chip alone. Pin5 is short to pin6. (We also measured a new chip which should be good chip, it's not shorted )

    The LED board is provided by our customer Chery, and they refuse to give detail information to us.

    Would you help to have a review on the driver board schematic? is there any mistake?

  • 0 in reply to Xiong JIANG
    Prodigy 180 points

    1. Whether the fault pin design is OK?  R2017(6.8k resistor) pull up to 3.3V, and connect to a MCU I/O port.

    2. Do you have any concern on the LED board design, what will happen if the LED board is a constant current circuit as showed in the schematic?

    The LED board designed constant current is 40mA, and our TPS92611 driver design current is 50mA(R2004 used 2ohm in BOM).

    3. Is there any sequence requirement on EN, PWM, fault, out,,,,

  • 0 in reply to Xiong JIANG
    Prodigy 180 points

    Sorry, LED schematic is below:

  • 0 in reply to Xiong JIANG
    Prodigy 180 points

    Hi Hailee,

    I found out voltage is higher than in voltage. 

    Vout is 12.7V while Vin is 12V.

    Whether this will damage chip?Vo Vin.xlsx

  • 0 in reply to Xiong JIANG
    TI__Genius 10040 points

    Hi Xiong,

    If Vout is higher than Vin, it is not a safe operating condition with the potential risk. This device is a linear LED driver which means the Vin should be always higher than Vout plus required headroom voltage.

    Additionally, could you provide the test waveforms of VSUPPLY and VOUT, and Iout, also what's the purpose of Q1 and Q2?

    Thanks!

    BR, Hailee.

  • 0 in reply to Hailee Xu
    Prodigy 180 points

    Hailee,

    See the Vo in below figure please, there is a overshot when it turn on.  Vin and Io is smooth with no overshoot.

    Why there is a overshoot? as you said, cause Vo even higher than Vin.

  • 0 in reply to Xiong JIANG
    Prodigy 180 points

    Hailee,

    The overshot seems not true, it's caused by incorrect oscilloscope.

    Whether the fault pin design is OK?  R2017(6.8k resistor) pull up to 3.3V, and connect to a MCU I/O port.

  • 0 in reply to Xiong JIANG
    TI__Genius 10040 points

    Hi Xiong,

    Why do you mean its incorrect oscilloscope? Please check this detail. What is the source of the 3.3V? Generally, it's okay. 

    BR, Hailee.

  • 0 in reply to Hailee Xu
    Prodigy 180 points

    we found only this probe have overshot, we use this prove test a stable voltage still have a overshot. (12V stable power supply and PWM wave in oscilloscope it self)

    we use other probes tested no overshot. we also confirmed the good probes can detect a real overshot.

    3.3V is a BUCK DCDC converter from 12V to 3.3V.

    Do you have some other concern?

    What will happen if our output current design to 50mA, and the LED load can not meet? for example: input votage is 12V while the typ voltage is 13V@50mA for LED board. 

    Do you have the out pin circuit in chip?

  • 0 in reply to Xiong JIANG
    TI__Genius 10040 points

    Hi Xiong, 

    Sorry, I don't have the OUT pin circuit inside, but for your question.

    1. if Vout exceeds the Vin+0.3 or Vsupply+0.6, means your operating conditions above our Absolute Maximum ratings. a damage can easily occur.

    2. Since your load is not only the LED, please calculate the output voltage and also see the measurement. just need to ensure under any circumstance, the Vout couldn't be higher than VIN. A potential risk is your DIAGNEN is always low, means your open diagnostic is disabled, the voltage difference between VIN and VOUT can't be monitored. even the OUT voltage exceeds the IN voltage, the device wouldn't report this situation.

    3. Additionally, what's the purpose of the Q1, Q2, R2, R3? for thermal improvement? from your schematic, you are doing the PWM dimming, what's the dimming frequency and duty cycle? you can monitor the Input voltage and output voltage/current to see the change while running. we need to check the failure condition for this damage. Thanks!

    BR, Hailee.