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TIDEP-0092: TIDEP-0092

John Manyala
Intellectual 410 points
Part Number: TIDEP-0092
Other Parts Discussed in Thread: AWR1642BOOST

Hi,

I'm looking at the Short Range Radar Reference Design TIDEP-0092 Resets and LEDS schematic and I'm struggling to understand how R103 can be 510 Ohms given that Q1 N-channel Mosfet (BSS123) has a drain current (Id) of 0.17A and Rds(on) @ 4.5V is 10 ohms. So Vds = 0.17A x 10 Ohm = 1.7V.

The LED at the drain of Q1 is TLMY1000-GS08 whose forward voltage (Vf) is 1.8V. So by my calculation, R103  = (5V - Vds - LED's Vf) / Id = (5V - 1.7V - 1.8V) / 0.17A = 8.82 Ohms, but R103 is 510 ohms per TIDEP0092. I'm propably missing something. 

Thanks,

John

  • 0
    TI__Guru*** 140784 points
    Hi,

    TIDEP-0092 is based on our standard AWR1642BOOST EVM.

    I will contact the hardware team about this question

    thank you
    Cesar
  • 0
    TI__Mastermind 26685 points
    Hello John,

    The LED only needs ~2mA of current to operate. 170mA is way beyond the LEDs absolute maximum DC forware current. Using the approximation of 510ohms from the resistor plus the 10ohms of the MOSFET we get around 3mA of current through the LED, which is well within the safe operating range.

    Regards,

    Adrian