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TPS62992-Q1: vset mode output voltage error

sijia dong
Prodigy 60 points

Part Number: TPS62992-Q1

This buck IC has two modes: vset and fb. I have some questions regarding the vset mode. The datasheet mentions that connecting a resistor with a specific resistance value to the vset pin can set the output voltage. However, I have two questions about these modes:

1. What is the internal circuit structure and setting logic of the vset mode? When the output voltage is 1.25V, the resistor is 95.3k. The resistor and the output voltage are not in a linear and monotonic order, which is not very logical and seems a bit strange.

2. The datasheet states that the resistor selection should meet 1% accuracy and 200ppm temperature drift. However, even if we select components according to this principle, during mass production, some components may still deviate from this requirement with a certain probability. Will this lead to abnormal output voltage? Have you conducted tests on such abnormal situations?
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  • 0
    TI__Genius 15230 points

    Hi Sijia,

    We will check and get back on this.

    Regards,

    Haseen.

  • 0 in reply to Haseen Reddy Siripi Reddy
    TI__Expert 6290 points

    Hi Sijia,

    Depending on the MODE pin setting it is either set to external feedback or VSET.

    For external feedback, we set output voltage by this equation: 

    If the device is configured to VSET operation, VO is sensed only through the VOS pin by an internal resistor divider. The target VO is programmed by an external resistor (RVSET) connected between the VSET pin and GND. Basically, here as external feedback but R1 is internal and value is set by R2 resistor as given in the table. So, it won't be monotonic or linear function.

    For other question with resistor having a deviation from recommended value slightly output won't be abnormal it will also change slightly.

    Hope this clarifies your queries.

    Best regards,

    Usha.

  • 0 in reply to Haseen Reddy Siripi Reddy
    Prodigy 60 points

    "Basically, here as external feedback but R1 is internal and value is set by R2 resistor as given in the table. So, it won't be monotonic or linear function.".This is where I'm confused. If the resistance of the Vset pin is r2 and the internal resistance is r1, is Vout still determined by the voltage division of r1? If that's the case, the larger the external resistance r2 between Vset and ground, the smaller Vout would be. However, this is clearly not the case according to the relationship table between Vset resistance and Vout. So, is the internal resistance r1 a fixed resistor or a variable resistor? Or is Vo determined by the size of the Vset resistance, through Vos voltage feedback, and configured by registers inside the buck IC?