• State TI Thinks Resolved
  • Locked Locked
  • Replies 7 replies
  • Answers 2 answers
  • Subscribers 64 subscribers
  • Views 168 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

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.

LM5164: Typical VIN pin impedance value

Stefano Franco
Prodigy 10 points
Part Number: LM5164

Tool/software:

Hi team,

 we use the LM5164 chip on many electronic boards and we are very satisfied.

I noticed that typically the impedance of the VIN pin (referred to the GND pin) is around 9MΩ.

The measurement is made with the chip not mounted on the electronic board.

In some cases, however, the impedance of the VIN pin is much lower than usual (even reaching 293kΩ).

I would like to ask if there is a typical VIN pin impedance value to use as a reference.

I would also like to ask if the impedance deviation of some chips should be considered as a waste or if it is normal.

Best regards,

Stefano

  • 0
    TI__Mastermind 34570 points

    Hello Sefano,

    I would not rely heavily on this measurement.  As long as there are not short circuits, I would think the device is good.

    Hope this helps.

    David.

  • 0 in reply to David Baba
    Prodigy 10 points

    Hi David,
    thanks for the replies.
    I wonder if you could anyway give me a minimum and maximum impedance value of the VIN pin so that I can set the limits in the ICT (in-circuit test) control that the assembler does.
    Another reason why I am concerned is that in the past, with other chips (of brands and models other than Texas), components that had deviations in the measurement of the impedances between the pins, have given problems to customers after several months of activity.

    Thanks again,
    Stefano

  • 0 in reply to Stefano Franco
    TI__Mastermind 34570 points

    Hello Stefano,

    Are you measuring the VIN pin in circuit?

    Thanks, David.

  • 0 in reply to David Baba
    Prodigy 10 points

    Hello David,

    We measure the equivalent impedance present on the network in which the VIN pin is also connected.
    The impedance of the network without the chip mounted is 92kΩ.
    Normally the impedance of the network with the chip mounted (and VIN pin at about 9MΩ) is 91kΩ (it is the parallel between the impedance of the circuit and that of the pin).
    If the VIN pin has a lower impedance than usual (for example 293kΩ), this causes the value of the equivalent resistance seen by the control to drop significantly. This goes from the typical 91kΩ to 70kΩ, causing the ICT control to fail (which is calibrated on a higher threshold).
    For this reason I ask whether such a large variation in the impedance of a pin is normal or represents an anomaly.

    To measure the impedance of the VIN pin with the chip mounted on the board, we raise the pin so as to disconnect it from the rest of the board and take the measurement on the pin (measurement referred to the GND pin).

    Thanks, Stefano

  • 0 in reply to Stefano Franco
    TI__Mastermind 34570 points

    Hello Stefano,

    Sorry it's not clear to me, is the device in circuit, i.e. do you have input capacitors and external components installed in parallel to the VIN pin to Gnd.

    Thanks.

    David.

  • 0 in reply to David Baba
    Prodigy 10 points

    Hello David,

     sorry if I didn't explain myself well.

    The chip is mounted in the circuit.

    On the VIN input pin there are capacitors and a 100k resistor connected.

    In addition there are R7 and R8 that affect the equivalent resistance.

    I attach the diagram.

    Thanks

    Stefano

  • 0 in reply to Stefano Franco
    TI__Mastermind 34570 points

    Hello Stefano, as I thought, you can reliably measure the impedance in circuit as the state of charge of the capacitors etc. will all effect reading.  

    I would say >100k you are fine.

    But again, this is not an exact test you can do in circuit.  As long as its not a short <10k you should be OK.

    David.