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LMR50410-Q1: Switcher circuit not working correctly

Ray Vincent Aranzaso
Mastermind 18180 points
Part Number: LMR50410-Q1
Other Parts Discussed in Thread: LMR50410QEVM

Hi,

Good Day. I have a customer who is working with LMR50410-Q1. Please see below his query for your reference. Thank you very much.

I've integrated two LMR50410Y5FQDBVRQ1 simple switcher circuits into my design and I'm having a problem with them. I used the sample circuit, and set them up with the proper components according to page 17 of the datasheet, one for 5V and one for 3.3V. The input supply voltage is 24V for both switchers. However, my output for the 5V supply is 24V, and the output for the 3.3V supply is around 1.7V, and is in hiccup mode. both circuits are virtually unloaded, save for a 3mA draw on each for an LED, and a few small DACs and Sensors. I anticipate the total draw on each to be about 100mA. 

I wanted to simulate in Web Bench, but the webpage said this part wasn't available for Web Bench yet. I fear at this point I might have blown my sensors and ICs on my board with the 24V feed from the 5V supply, but I still need to lock down what happened.  I'd appreciate a Monday phone call to help get me back on track.

Best Regards,

Ray Vincent

  • 0
    TI__Genius 10715 points

    Hello Ray,

    The LMR50410Y5FQDBVRQ1 is a fixed 5V output device meaning that it is expecting a feedback voltage of 5V. The feedback resistors provided in Table 9-1 of the datasheet are meant for the adjustable output voltage option of the device which expects a feedback voltage of 1V. This is what is causing the discrepancy in the output voltages seen by the customer. 

    For the 5V supply, the customer should connect the output voltage node directly back to the FB pin of the device. 

    For the 3.3V supply, the customer will need to use either LMR50410Y3FQDBVRQ1 (fixed 3.3V device), LMR50410YFQDBVRQ1 (adjustable FPWM device), or LMR50410YQDBVRQ1 (adjustable PFM device). The fixed 3.3V option will require a direct connection between the output node and the FB pin while the two adjustable options will require the FB resistor values mentioned in table 9-1. 

    Regards,

    Harrison Overturf 

  • 0 in reply to Harrison Overturf
    TI__Mastermind 18180 points

    Hi Harrison,

    Good Day. Please see below the response of our customer to your reply. Thank you very much.

    I don't suppose you guys have at least any engineering samples of LMR50410Y3FQDBVRQ1 by chance do you? I have 5 prototype PCBs that just came in, and no one else has stock anywhere; and this needs to fit in a tight space, so I can't put a brick on it. Any chance of that?

    Best Regards,

    Ray Vincent

  • 0 in reply to Ray Vincent Aranzaso
    TI__Genius 10715 points

    Hi Ray,

    It looks like we don't have any loose samples available at the moment. We do have samples of the LMR50410QEVM available which comes with the LMR50410YQDBVRQ1 (adjustable version, so they would need the feedback resistors) on it. You could order this board and have the customer transfer the IC from the EVM to their board. 

    Regards,

    Harrison Overturf