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TPS62868: VOUT operation

Marvin Gasis Arcangel
Genius 9505 points
Part Number: TPS62868
Other Parts Discussed in Thread: TPS62865

Hi Team,

Can you help me understand how Start-up sequence and setting up VOUT works?

The datasheet states that, during start-up, the device sets the internal reference voltage, and determines the start-up output voltage through the resistor connected to the VSET/VID pin. Then during the ramp-up period, the output voltage ramps to the start-up output voltage first, then ramps up or down to the new value when the value of the output register is changed by I2C interface commands.

If I'm not using I2C, will the Vout be maintained by the VSET/VID’s resistor?

For example, if I wanted an output of 0.3V~ 0.5V, during start-up period, a resistor=133Kohm is connected to VSET/VID, then Vout= 0.5*1.00V =0.5V. Correct?

Then after start up, VSET/VID: resistor=133Kohm to GND. Vout is still =0 .5V?

Then If I were to DVS to change the output to 0.3V, how can I do this without I2C? I understand that the VID pin must be at 0.84V for H and 0.4V for Low to switch register but I don't understand Table 8-6 and Table 8-7. Can you help?

Great thanks!

Regards,

Marvin

  • 0
    TI__Guru*** 144430 points

    Hi Marvin,

    After startup, the device regulates to the voltage in the Vout 1 or 2 registers.  Section 8.4.4 explains how the VID pin chooses between Vout 1 and Vout 2.

    If you don't use the I2C bus, then the device will only output those voltages.  Changing the VSET resistor after startup has no effect on Vout.

    We also offer the TPS62865, which has the traditional FB pin instead of I2C.

    Does that help?

    Chris

  • 0 in reply to Chris Glaser
    TI__Genius 9505 points

    Hi Chris,

    Thank you for your response.

    Chris Glaser said:
    If you don't use the I2C bus, then the device will only output those voltages.  Changing the VSET resistor after startup has no effect on Vout.

    If changing the VSET resistor after start-up has no effect on Vout, then how can I implement the dynamic voltage scaling?

    Regards,

    Marvin

  • +1 in reply to Marvin Gasis Arcangel
    TI__Guru*** 144430 points

    Hi Marvin,

    Page 1 of the D/S says: ...dynamic voltage scaling (DVS) through I2C

    You need to use I2C to dynamically adjust the output voltage.  Do you have a different way that you would like to change the voltage?

    And page 6 of my paper discusses the VSET resistor and R2D converter setting the voltage at one value: www.ti.com/.../slyy180.pdf

    Chris