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TPS92661-Q1 / Calculation of Rds(on)

Ryuji
Guru 20090 points

Hello,

Could you please let me know the Rds(on) calculation detail?

I found that the calculation of Rds(on) from the datasheet P.11.
However this case use R(ALL)(ON)(max).Thus, this value includes Resitance of 2wire only.

For example,

If 1wire=40mohm, Rds(on)=140mohm,

Case 1 : Most upper side 1pc LED only on.

In this case, 2wire x Rds(on)*11

Case 2 : Center 1pc LED only on.

In this case, 4wire x Rds(on)*11

 

Thus, I think that we can’t use the calculation of the datasheet P.11 which used R(ALL)(ON)(max).

 

Best Regards,
Ryuji Asaka

  • 0
    TI__Mastermind 44590 points

    HI Asaka-san,

    The RDSON measurement is for our internal FET(s).  The measurement is as follows:

    This is not the forward voltage of the LED's as that is a function of the LED's used in the application. So this calculation on page 11 help you to understand the worst case power dissipation for the TPS92661. This does not cover the power dissipation of the LED's. For LED power loss you would have to add in ILED*VFLED for each scenario you wish to calculate.

    I hope this helps.