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LP8720: PD value calculation

KIM Andy
Expert 2530 points
Part Number: LP8720

HI

Can I calculate the maximum current I can assume when all the LDO outputs of the LP8720 are assumed to be 1.8V?
Do I have to add up PD = (Vin-Vout) xIout for each channel like the original LDO calculation?
If so, can you check if my formula is correct?

Condition
VIN = 3.5V, VOUT = 1.8V, IOUT = 0.3A
R? JA = 45 ° C / W, TJ = 50 ° C

PD = (VIN - VOUT) x Iout
          (3.5-1.8) x 0.3 = 0.51
4ch LDO PD = PD x 4ch = 2.04

P = (TJ-TA) / R? JA
TA (MAX) = (PxR? JA) - TJ
                   = (2.04 x 45) - 150
                   = 58.2
In conclusion, design is possible at TA 58.2 ° C or less.
Is the above calculation correct? dcdc is not used.

  • 0
    TI__Genius 10885 points

    Hi Kim,

    This is a reasonable approximation, but thermal performance is also highly dependent on the layout and PCB operating temperature and not just the Junction-to-Ambient resistance. 

    You are correct that the dissipation from each LDO should be combined for the total power dissipation in the regulators. There will also be some additional quiescence currents in the device, but they should negligible compared to the losses in the LDOs.

    The total power dissipation is correct at approximately 2.04W for sustained maximum load currents under these conditions.

    Best Regards,

    Rick S.