• State
  • Locked Locked
  • Replies 2 replies
  • Subscribers 63 subscribers
  • Views 251 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

TPS735xx EN line

Paul Lander
Prodigy 230 points

In my circuit a TPS73533 has 3.5V at VIN for 500 microseconds before an MSP430 takes control of the EN line. The EN pin floats during this time because the MSP430 is starting up and its port pin that is connected to EN is Hi-Z. Connecting a 1 MOhm resistor between EN and GND is sufficient to keep the TP73533 in shutdown, but does anyone know of a more elegant solution?

  • 0
    TI__Expert 8890 points

    Hi Paul,

    The TPS73533 is guaranteed to be disabled when Ven is less than or equal to 0.4V.  If your 1Mohm resistor is pulling down that EN well below 0.4V then your solution is as elegant as it gets.  On the other hand if that voltage is actually hovering/floating just near 0.4V, then I might try a two fet circuit that depends on the turn-on threshold of the FET (1V).  To be sure, this is less elegant than a simple resistor pulldown but effective if necessary. (see attached diagram)

     

    8156.Doc1.doc

    Regards

    Bill

  • 0 in reply to Bill Stokes
    Prodigy 230 points

    Hi Bill,

    Thanks for the circuit. In my case touching the EN pad with a scope probe 'always' works, which implies a very light tie-down of 1 Mohm. I am using the TPS73533 as a dedicated Wi-Fi power supply and I haven't encountered this problem with other LDOs. A couple of round-up questions that might be useful to the community:

    1. In general, are enable pins on regulators customarily some predictable input style, such as open drain?

    2. I would rather use a TPS78233 as a low-cost, low-quiescent current LDO, but I am concerned about meeting the Wi-Fi peak current demand. In general, is there a reason that the peak current capability of a regulator cannot be partially specified in joules, i.e. volts * amps * seconds, so that a generic LDO + output capacitance could be designed for transient-load situations?

    Paul