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POR for PCA9534A

Other Parts Discussed in Thread: PCA9534A, TCA9534A

 

Dear Technical Support Team,

 

I have a question about POR for PCA9534A.

Customer has a problem of POR, so they have a plan to change it to TCA9534A.

But we'd like to know the POR specification of PCA9534A.

 

1.)

Should correct POR be satisfited with both Figure 31 and Figure 32?

Especailly Figure 31 seems that VCC should be Below 0.2 V for POR.

If POR is satisfited with only Figure 32(Por Threshold), dosen't PCA9534A get correct POR?

 

2.)

VCC_FT has range from 1 ~ 100ms. If POR isn't satisfited with it, dosen't PCA9534A get correct POR?

 

Best Regarads,

y.i

  • Hello Y.i,

    THanks for the question.

    Allow me to try and explain the POR requirements.

    In Figure 31, this shows the POR which occurs from a complete power off (device power is cycled off).

    In Figure 32, this shows a POR which occurs when the voltage drops below the POR level, but not completely to 0.

    They have similar timing restrictions at how much time they must spend below the POR(min) threshold. Therefor, technically figure 32 is the only 'limiting' POR requirement. Figure 31 is essentially a sub-set of figure 32 (where the voltage it drops to is 0V).

    So now, to answer your questions.

    1) A correct POR can occur with either condition, but figure 32 is the more 'strict' POR requirement (since figure 31 is the same as 32, but goes to a lower voltage, so it's considered the "safer"/more head room POR).

    2) If the fall rate or rise rate of the device are not satisfied, it is possible that a POR will be missed. HOwever, the fall rate is not quite as critical as the rise rate (if the voltage goes to 0V). If the voltage is just falling down to VPOR(min), then the fall rate is more of a requirement, because the POR circuitry will be powered the entire time and looks at the fall rate.

  • Hi Jonathan,

     

    Thank you for your reply.

     

    I have more questions about the fall rate for POR, if power is on and off continuously (onoffonoff・・・).

     

    Fall rate is 4sec, so the device is not satisfied with VCC_FT1 100ms). At this time , the Vcc doesn't go to completely 0V.

     

    when power-on after this condition, does the device have risk of incorrect POR?

     

    Customer faces intermittent POR issue. For Example, default direction is input, but sometimes it is output after re-power-on.

     

    Best Regards,

     

    y.i

  • Hello Yi,

    You are correct. Your fall rate would violate the POR spec and there is a chance that your device will not have a valid POR when you power it back up. I would recommend stepping up to the TCA9534A. It is P2P (depending on your package).