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LMZ31530: Vout Calculate

Kuan Wei Chen (Kevin Chen)
Genius 9710 points
Part Number: LMZ31530

Dear Team,

If my customer use this module for 0.88V, how to calculate it?

Do we have equation for it?

BR

Kevin

  • 0
    TI__Genius 17905 points

    Hi Kevin,

    If you plot Vout vs Rset from the datasheet table, you'll find that the curve is smooth, and you can interpolate an Rset value for the target 0.88V output. Using the PVIN=12V curve, I interpolated a target Rset = 3105ohm to get Vout = 0.88V, with closest standard resistor value being Rset = 3090ohm.

    Usually, converter/module datasheets give the equation Vout = Vref * (1+Rtop/Rbot) or similar. The LMZ31530 has a Rtop = 1.43kohm inside the module as shown on datasheet p.8, leaving the external Rset as the bottom resistor Rbot. However, as described in the 2nd paragraph of the snippet you have above, this LMZ31530 device regulates the valley of the voltage ripple at the Vadj pin, which would amount to a small average output voltage offset if using the typical simple feedback formula to calculate resistor values. This Rset resistor table was intended to help customers determine the right Rset resistor value for their target output voltage more accurately.