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TPS542A50: Higher /Lower Output Voltage Adjustment

Johnsin Tao
Intellectual 1625 points
Part Number: TPS542A50

Hi  engineers:

     I can't  understandy the "Higher Output Voltage Adjustment"  and the "Lower Output Voltage Adjustment" in the TPS542A59  datasheet page22?

    How di I set the output voltage by them?

    Thanks.

    Best wishes!

    Johnsin tao

  • 0
    TI__Prodigy 400 points

    Hi Johnsin,

    The output voltage is set using external resistors to create a voltage divider on the VSET pin. This VSET LSB is the VSET value divided by 3583. The VOUT ADJUSTMENT TARGET is the desired adjustment, and the values provided in this column are example values. For example, the fifth row down in Table 7-9 is to increase a set output voltage of 1.8 V by 5% (90 mV).

    VOUT LSB is the VSET LSB multiplied by 5 to account for the internal 5:1 voltage divider between the RSP and RSN feedback pins.

    The VOUT ADJUSTMENT STEP is the decimal value of the value to be written to the VOUT_ADJ1 and VOUT_ADJ2 registers.

    Here's what may be unclear:

    To increase the output voltage, the VOUT ADJUSTMENT STEP is converted to binary, and the 16 bit value is written to VOUT_ADJ1 and VOUT_ADJ2.

    To decrease the output voltage, the VOUT ADJUSTMENT STEP is converted to binary, and then the 2's complement of that value is written to VOUT_ADJ1 and VOUT_ADJ2.

    Figure 7-4 that shows the 4 most significant bits of VOUT_ADJ1 register needs to be corrected. The 4 most significant bits of VOUT_ADJ1 are read/writable, the same as the VOUT_ADJ2 register.

    So, to increase an output voltage of 1.8 V to 1.85 V, write a "0000 0000" to VOUT_ADJ1 and a "1011 0100" to VOUT_ADJ2.

    I hope this helps.

  • 0 in reply to Kevin Bradford
    TI__Intellectual 1625 points

    Hi  engineer:

         According to the reply,  in the line 5  of the table 7-9 :

        Increasing the output value by 5%, so that is, 5% of 1.8V  is  90mV. The corresponding binary code is 1011011010. However, the binary code is adjusted from 1.8V to 1.85v, and the difference is only 50mV, which does not correspond to 90mV above. Why?           

        In addition, if the output is 3.3V, then Vset is equal to 3.3v/5 = 0.66v, then Vset LSB = 0.66v/3583 = 0.184mv, Vout LSB = Vset LSB * 5 = 0.921mv. If I increase Vout by 20mV, i.e. 3.32v, then Vout adj Step = 20mV / 0.921mv = 21.7, and 22 is taken, the binary code should be 0001 0110. Is this correct? 

        Thanks.

        Best  wishes!

        Johnsin Tao

  • 0 in reply to Johnsin Tao
    TI__Prodigy 400 points

    Hi Johnsin,

    The decimal to binary conversion of 180 is 10110100. Keep in mind that the VOUT LSB is 0.5 mV, and the VOUT ADJUSTMENT STEP are discrete unitless steps limited by the VOUT LSB. With this in mind, it takes 180 increments of 0.5 mV each to make a 90 mV change. Please let me know if you think I am misunderstanding you here.

    As to your second questions - yes, you are correct. When we rev the datasheet to fix the VOUT_ADJ1 register, perhaps we will add a sample calculation or two for determining the binary code that corresponds to a given change in output voltage.