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TPS54232: Understanding UVLO threshold and Hysteresis

Spandan89
Expert 1420 points
Part Number: TPS54232

Hi,

Input Voltage: upto 24VDC

Output voltage: 7V and then it goes to 5V LDO to power 5V MCU.

I am trying to understand how UVLO works and hysteresis. In the datasheet, it is recommended to add hysteresis using Ren1 and Ren2 resistor. Ven voltage is set to 1.25V internally. I selected Vstart = 10V and Vstop=8V. This gives me Ren1 = 666.66K and Ren2 = 112.35K. Using these resistor values, voltage at EN pin comes to 3.46V with 24V input. But during the startup when the input voltage is rising from 0V gradually to 24V, when does TPS54232 start switching? what is that voltage? 

Idea is to start TPS54232 switching only when input power reaches, lets say, 10V or 12V. is there a relation between voltage at ENABLE pin and voltage at which TPS start switching?

One more thing, how do I calculate the hysteresis voltage? is it a difference between Vstart and Vstop?

I did read SLVA769A. in that, it says the datasheet should have VIT+ and VIT–. but TPS54232 datasheet doesnt have that information.

Thanks in advance.

  • 0
    TI__Genius 10070 points

    Hi,

    If you set  Vstart = 10V and Vstop=8V, The calculated value should be Ren1 = 666.66K and Ren2 = 88.5K, When the input voltage increase to about 10V from 0, the IC starts switching. And when the input voltage drops to about 8V, the IC stop switching.

    The hysteresis voltage=10V-8V=2V

    Shawn