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TPS61500: TPS61500 output current problem

Carlo
Expert 7715 points
Part Number: TPS61500

Hi team, 

Good day.

Our customer needs assistance with the situation they were encountering in using the TPS61500. Please help with the PCB and schematic review. Here are the details provided to us.

"I wanted to contact you because I have a suspicion that I was sold some defective TPS61500 3A Boost constant current ICs from one of your suppliers, LCSC. I have tried changing everything on my design from inductor values, output capacitors, switching frequency setting, Current set resistor value but to no avail. The IC doesn't seem to supply more than 1.3A. Although I do have to point out that it seems to be working properly for lower currents of approximately sub 800mA.

I have put together quite a few boards but they all seem to have the same Issue. I ran the formulas in the datasheet for calculated max output current and I am getting a calculated max of 2+ A. Furthermore the waveform on the oscilloscope doesn't look all that great and it differs vastly from the one in the datasheet. Testing conditions are as following: Voltage on the Input: 3.91V RMS, Output voltage 4.52v RMS. Frequency set resistor 100killo Ohms, Voltage divider values for OVP 120k and 21k Ohm resistors respectively. Inductor value is 22uH with an Isat of 3A from Panasonic. Current set resistor is 0,095ohms. Diode is a DIYI brand 5A 40v 225mv measured drop SBD. Output cap configuration consists of 5 4.7uF 1206 size TDK X7R capacitors rated at 50v. Soft start capacitor is a 22uF TDK 1206 cap rated at 10v. All of my components including the TPS61500 are from LCSC. "

Attached is the schematic and PCB layout. Thank you for your assistance.

Schematic and PCB.zip

Regards,
Carlo

  • 0
    TI__Genius 13001 points

    Hi Carlo,

    Could you please provide the corresponding waveforms of SW, Vout, inductor current for further analysis?

    BR,

    Robin

  • 0 in reply to Yuting Shao
    TI__Expert 7715 points

    Hello Robin,


    Our customer will be loading it with 7 BY255 diodes in series to simulate an LED, will this be okay for the current measurement?

    Regards,
    Carlo

  • 0 in reply to Carlo
    TI__Expert 7715 points

    Here is the waveform for the SW.

    And for the Vout

  • 0 in reply to Carlo
    TI__Genius 13001 points

    Hi Carlo,

    I don't think it's a good idea to simulate LED characteristics by diode since diode voltage drop is not similar with LED.

    For Vout waveform, is there plot by DC coupling?

    BR,

    Robin

  • 0 in reply to Yuting Shao
    TI__Expert 7715 points

    Hi Robin,

    Good day.

    According to our customer, they do not have high power LEDs that match their design's output current and voltage requirements. Here is the waveform provided and it kept falling out of oscillation. According to them, it behaves the same under a laser diode load which acts identically to an LED but is even more sensitive to thermal runaway.

    Please let me know if you need further details.

    Regards,
    Carlo

  • 0 in reply to Carlo
    TI__Genius 13001 points

    Hi Carlo,

    Please refer to the below diode I/V curve. For larger current (e.g. 1.3A), it will need much larger voltage than normal LED, which may beyond the TPS61500 output range. However, for 800mA, TPS61500 may have the capability to boost.

    So, please convince the customer try again with LED.

    BR,

    Robin

  • 0 in reply to Yuting Shao
    TI__Expert 7715 points

    Hi Robin,

    According to our customer, the device performed the same with an LED load not supplying more than 3A with the led's VF being 4.5 and the driver is powered by a 4V 9A source. They designed the drivers since it claimed in the datasheet of handling 3A and boosting. The max VF of their design had to meet  4.7vF LED powered by 4V and an output current of 3A. Can the TPS61500 support this?


    Regards,
    Carlo

  • 0 in reply to Carlo
    TI__Genius 13001 points

    Hi Carlo,

    Yes, TPS61500 supports 3A@min current limit. But it must be pointed out that 3A is just the inductor peak current instead of average current. So for actual application, the average output current is lower than 3A.

    BR,

    Robin