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TPS65217 DCDC Adjustable Voltage

Other Parts Discussed in Thread: TPS65217, TPS65014

I am using a TPS65217C in a non-AM335x application, and I need the device to start up with DCDC2 at 3.3V (not 1.1V).  This 3.3V will power the processor that controls the I2C to the TPS65217.

I do have the EVM, which I was successfully able to bring up using the GUI.  I decided to cut the trace going from the L2 output back to VDCDC2, and I kludged in a voltage divider to take 3.3V down to the vref voltage (0.6V).  270k/60kohm.

Now when I power up, all of the rails are disabled? In the GUI, I switched XADJ2 to '1', the flipped the 'GO' bit, and still nothing.

Am I missing something here?  Maybe instead of designing for vref to 0.6V, I should use 1.1V?

  • Hi Kevin,

    It looks like you've violated the power good signal.

    "Power-good is a signal used to indicate if an output rail is in regulation or at fault. Internally, all power-good

    signals of the enabled rails are monitored at all times and if any of the signals goes low, a fault is declared. All

    PGOOD signals are internally deglitched. When a fault occurs, all output rails are powered down and the device

    enters OFF state." (page 19 of data sheet)

    The threshold hold of the Power good signal for output voltage falling id 90% of set voltage, at .6v you are at about 54%, causing a fault and sending the device into off state. If you repair the trace and remove the external voltage divider the part should come back up. The power up sequence and the voltage each DCDC and LDO start at is something kept in the EEPROM of the device. If you want to power up at 3.3V it would have to be changed in the EEPROM.

  • Thank you for your quick answer!

    So based in this, the part will need to be preprogrammed in order to power up at 3.3V?  There is no way for the part (out of the box) to power up at 3.3V without configuration?

  • Theoretically it is possible to power up using an external resistor; however, we cannot guarantee the performance of the device: The Feedback pin is fed to an internal resistive voltage divider, which divides the FB pin voltage down to match the internal 0.6 reference voltage.  The internal divider has an approximate total resistance of 1MOhm, so the external divider must be significantly stronger than the internal one (<10kOhm total resistance); If you choose to move forward with this suggestion design with 1.1V in mind not 0.6V. What processor are you using? What is your application?

  • We are using a freescale VYBRID processor (3.3V) paired up with DDR3(1.5V), so the only requirements of the PMIC is to provide these two rails and be able to handle the battery bridge/charging.  I'm thinking about switching to the TPS65014