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TPS272C45: FLT pin output issue

Anna
Intellectual 995 points
Part Number: TPS272C45

Hi Dear，

1-The customer uses TPS272C45D, and the initial circuit is as follows.When testing in an open or short circuit, the low level output of the FLT PIN pin is measured to be around 2V, not 0V. What is the reason？

2-The customer has made modifications to the schematic diagram, as shown in the figure.

In the case of an open circuit or short circuit, the low level output of the FLT pin is measured to be around 0.74V, which is sometimes recognized as high level by the MCU. May I ask if 0.74V is a normal output？

. 

  • 0
    TI__Genius 16035 points

    Hello, 

    Based on your ground network, the design appears to shift ground up to a max 1.25V.

    Is it possible the customer is measuring the FLT pins in reference to system ground rather than IC ground? 

    Best Regards, 

    Elizabeth 

  • 0 in reply to Elizabeth Higgins
    Intellectual 995 points

    Hi Elizabeth,

    The customer measured that the voltage difference between FLT pin and IC GND was close to 0V, but due to the presence of diode BAS21, the measured voltage difference between FLT pin and system GND was 0.74V. A voltage of 0.74V, sometimes recognized by the MCU as a high level.

    The customer wants to lower the low level of FLT further and is considering the following two options:

    1-In the reference design, the diode BAS21 is connected in series with a 48.7 ohm resistor. Does this resistor have a current limiting effect? Can we lower the FLT level by removing the resistor

    2-Are there any recommended diodes with lower conduction voltage drop? Can I switch to a Schottky diode？

  • 0 in reply to Anna
    TI__Genius 16035 points

    Hi Anna, 

    Thank you for your response. I am inquiring with the team whether we have a recommended diode. 

    Best Regards, 

    Elizabeth 

  • 0 in reply to Elizabeth Higgins
    TI__Genius 16035 points

    Hi Anna, 

    1-The 48.7 ohm resistor in series with the BAS21 diode is not needed. I would recommend removing the 48.7ohm resistor and shorting across it. 

    2-you could use a Schottky diode, however we do not have any specific recommendations for lower forward voltage drop diodes

    Best Regards, 

    Elizabeth 

  • 0 in reply to Elizabeth Higgins
    Intellectual 995 points

    Hi Elizabeth,

    The reverse withstand voltage of Schottky diodes is much lower than that of BAS21. How can I choose the reverse withstand voltage value in such applications if I switch to Schottky diodes

  • 0 in reply to Anna
    TI__Genius 16035 points

    Hi Anna, 

    Yes it is important to take note the reverse standoff voltage is lower than that of the BAS21. It is up to the customer whether that specification is needed. 

    The diode needs to be chosen based on your application requirements. However, before switching diodes, I would recommend removing the excess resistor as it is not needed for the functioning of this device. This should resolve the issue. 

    Best Regards, 

    Elizabeth