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LMG1020EVM-006: TIDA-01573 Power Loop Capacitors

Katsuhiko Kaizawa
Intellectual 2045 points
Part Number: LMG1020EVM-006
Other Parts Discussed in Thread: TIDA-01573

Hello support team,

My customer would like to understand equation(1) in the TIDA-01573.
http://www.tij.co.jp/jp/lit/ug/tidue52/tidue52.pdf

In p.4, equation (1) : 60A*1ns/2V = 30nF capacitance

In this case, 2V means 5% of Vbus 40V. Is this right?
If so, worst case voltage across a laser diode is 38V.
Should not 38V be used for the capacior calculation instead of 2V?


Best regards,
Kaizawa

  • 0
    TI__Expert 3225 points

    Hi Kaizawa,

    Yes you are right. 2V means 5% of 40V. Assuming you have this capacitance close to the FET and diode, this cap will become the major source of transient current, and its voltage will drop according to our calculation. This equation is using charge to calculate the needed capacitance to hold the DC voltage stable.

    Thanks and regards,

    Lixing