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PCA9544A: typical power dissipation

Bertram Brummer
Intellectual 1906 points
Part Number: PCA9544A

Hi,

the 400mW total power wc is for my power derating too conservative and I would like to get some typical numbers for the following config:

PCA9544A

TSSOP20 package

VCC = 3.3 V

bus speed = 100kHz

all pull-up resistors are 4k7

slaves on all 4 channels connected, but only one channel enabled simultaneously

is there a tool or an estimator to get a typical power number for this device? Or can you maybe simulate this?

regards, Bertram

  • 0
    TI__Mastermind 23406 points

    Hello Bertram,

    400mW is what the package can handle.  The devices doesn't really dissipate much power.  The power dissipation will be dependent on the frequency, the capacitive load on the bus, the voltage level, and the bit pattern.  Most of the power dissipation occurs in the switch due to it's resistance.  The switch resistance ranges from 9-16 Ohms typical depending on the Vcc.  Lets assume worst case the bus is held low, which means the pass FET connects the pull-up resistor to ground, therefore we have a current of ~3.3V/4.7k Ohm = 0.7mA.  Assume worst case Rsd on of switch to be 20 Ohms, that means the switch would dissipate I^2*Rsw=0.01225 mW.  Even if you double this we are the low single digit milliwatts.  The device circuitry dissipation would be max of 12uA at 3.6V, that means 43uWatts.  I don't know of a good tool that could do a very accurate power dissipation.  Generally speaking these parts dissipate very little power and the junction temperature is approximately what the case temperature is. 

    -Francis Houde