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TCA9517: Power on sequence too long issue

Part Number: TCA9517

Dear Team:

Q1. U6 enable should change to P3V3, not P3V3_AUX ? ?
What would happen if U6 EN pull up to P3V3_AUX ? Is it not allowed? èWhat is different between P3V3 and P3V3_AUX?  It is ok about VCCA=VCCB=3.3V.?
note: power sequence: P3V3_AUX à P3V3 à P1V8 è I think the turn on delta time is around us, right??
P3V3_AUX is standby power, P3V3, P1V8 are main power, need push power button to power on from standby power to main power, it usually takes few seconds or longer to power on.

  Are Q1, Q2 still ok? If P3V3_AUX power on but P3V3 not, would it have electric leakage from P3V3_AUX to P3V3 due to wrong power up sequence of TCA9517?

Q2.   U5 enable pull up to P3V3_AUX.
Pull up sequence: VCCB and EN pull up to P3V3_AUX first, than VCCA pull up to P1V8 ?

Is the pull up sequence ok? Would it cause any problem?      èIt is OK. ?

 

P3V3_AUX – few seconds or longer à P3V3 --few usà P1V8

U5 EN PU to P3V3, Is it ok ?

U6 EN PU to P3V3, is it ok?  ( maybe there are few mV between P3V3 and P3V3_AUX, Is that ok?  What is the allowed max voltage gap between VCCB and EN ?)

  • Hey Thomas,

    I think it would be easier if you upload a schematic so I can get a better sense of the set up. I'll try to answer what I can from what you have but I am assuming U5 and U6 are both our TCA9517 device. Correct me if I am wrong.

    "Q1. U6 enable should change to P3V3, not P3V3_AUX ? ?
    What would happen if U6 EN pull up to P3V3_AUX ? Is it not allowed? èWhat is different between P3V3 and P3V3_AUX? It is ok about VCCA=VCCB=3.3V.?"

    -VccA=VccB=3.3V is okay. Pulling EN to 3.3V isn't an issue but because it is a different power source than what is on VccB, you may see some small current being drawn or supplied between the two power source because EN pin an internal pull up resistor to VccB.

    "If P3V3_AUX power on but P3V3 not, would it have electric leakage from P3V3_AUX to P3V3 due to wrong power up sequence of TCA9517?"
    -I believe so, there is a pull up resistor from the EN pin to VccB. I don't think the device will be damaged though. EN pin is high impedance.

    "Pull up sequence: VCCB and EN pull up to P3V3_AUX first, than VCCA pull up to P1V8 ?"
    -This should be fine, the device does the actually turn on until VccB> 2.5V AND VccA>0.8V

    "Is the pull up sequence ok? Would it cause any problem? "
    -My understanding of the TCA9517 device is this kind of start up is fine. The device has the requirement of both VccA and VccB needing to be above a certain threshold value before actually turning on. If the conditions are not met, the drivers will remain high impedance and not pass signals.

    "maybe there are few mV between P3V3 and P3V3_AUX, Is that ok?"
    Should be fine. Like I stated above, there is a pull up resistor between EN and VccB so you may see some current between these two points.

    "What is the allowed max voltage gap between VCCB and EN"
    -This is not something we've tested for. I think if VccB>2.5V and EN is 0.7xVccB then the device should still function.

    Thanks,
    -Bobby