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TPS701: Feedback Resistor

Brian Wang0928
Genius 14030 points
Part Number: TPS701

Since TPS70102 is now in shortage, we suggest customer to use TPS70151 instead. In customer application, MCU/F2812 needs both 3.3V_IO and 1.9V_Core power. 

however, the TPS70151 offers fixed output voltage of the 3.3V and 1.8V. We're considering if adding an external resistor to the FB pin that could adjust the output voltage from 1.8V to 1.9V. is that possible? Or any effective way?

What's the resistor divider value of the TPS70151 for 1.8V output rail? In the e/c table, the feedback current is 1uA,typ at Voltage on the FB pin is1.8V. Does it mean that the inner resistor divider is 1.8M Ohm? how is the low side and high side value of the resistor divider? 

Regards

Brian W

  • 0
    TI__Genius 12960 points

    Hello Brian,

                      TPS70151 is a fixed out version of the device, and therefore the FB pin is not accessible for us to change the resistor values in the resistor divider. This device has a SENSE pin accessible and there is an internal 10K resistor connected between the OUT and SENSE pins. It could be possible to add an additional resistor between SENSE and OUT pins and effectively increase the value RFB_TOP. Whether 1.9V of VOUT can be generated would depend on the values of the feedback resistors. Please note that the SENSE and OUT pins are typically to be shorted together and adding a resistor instead between them could cause instability. Please provide us a week to verify the values of the feedback resistors. Thanks!

    Regards,

    Srikanth   

  • 0 in reply to Srikanth Lolla Venkata
    TI__Genius 14030 points

    Hello Srikanth,

    I'm a little confused about your comments. Here please find my feedback and questions. thanks. 

    1. When there is an external Resistor added and connecting between VOUT and VSENSE in parallel, the total equivalent resistance value for the inner 10K Ohm and ext. resistor will be smaller, correct? if so, the RFB_TOP should be smaller than 10K Ohm?

    2. You mentioned adding a resistor between VOUT and VSENSE pin, it could cause instability? why?

    3. What's the value of the inner resistor value? is it 1.8M Ohm as the input leakage FB current is 1uA specified on e/c table?

    4. I'd like to correct my customer request here. What customer really need with TPS70151 is to change VOUT1 to 1.8V(Fixed 3.3V), and change VOUT2 to 3.3V(Fixed 1.8V). is that possible to adjust voltage on TPS70151 by workaround solution?

  • 0 in reply to Brian Wang0928
    TI__Genius 12960 points

    Hi Brian,

                 Please note that the net value of RFB_TOP_NET will be the sum of this equivalent resistor (parallel combination of 10K and external resistor) and the actual RFB_TOP in the device, RFB_TOP_NET = REQ + RFB_TOP. This can be understood by looking at the block diagram in page 7 of the datasheet. The risk of instability is very small and would be caused only due to parasitic's. There would be no way to realize a smaller output voltage value (3.3V to 1.8V) using the TPS70151 device. The chance of realizing a higher value (1.8V to 3.3V) is also very small, but I need to retrieve the internal feedback resistor values to make a conclusion. Thanks!

    Regards,

    Srikanth