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TPS7A84: Using ANYOUT for >3.95V

Tom Carpenter
Prodigy 80 points
Part Number: TPS7A84

Hi,

We have been using the TPS7A84/5 and other ANYOUT devices in a few applications so far. In several of them we have needed a 5V rail, and so end up with two external precision resistors to control the output voltage. This uses up space and adds to component cost due to the need for two different high tolerance resistors.

Having come to use the regulators again in another design, implementing the circuit it's dawned on me that it should be possible to achieve the desired result using just a single resistor. For ANYOUT, there is any internal high tolerance 12.1k resistor between SNS and FB. For Adjustable we end up adding an external 12.1k resistor between SNS and FB. So why not just use this one in adjustable mode?

For example, could I simply add an external 6.04k 0.1% resistor between FB and GND (a standard E96 series resistor that is effectively within 6.05k 0.5%). This should in theory be equivalent to adding a second 1600mV ANYOUT pin. If I then tie the 200mV, 800mV, and 1600mV ANYOUT pins to GND as well, this should give me 5V.

Is there any detriment to performance that I am missing here?

Kind Regards,

Tom.

  • 0
    TI__Guru 55940 points
    Hi Tom,

    While using both external resistors and internal ANYOUT resistors at the same time should not damage the LDO, it is not recommended to use both the internal ANYOUT resistors and external resistors at the same time. Our test program ensures the internal resistor ratio rather than the value of the internal resistors. This adds a potentially large source of inaccuracy when attempting to match external resistors to the internal resistors. As such we recommend using only external resistors or the internal ANYOUT.

    Very Respectfully,
    Ryan