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Fixed output variant impact on accuracy

david degraaf
Prodigy 20 points

Hello,

I'm designing for an application that requires extremely high accuracy (+/-2%) over load/line/temp/process. There are three rails:
1V0 >= 2.5A
2V5 >= 2.5A
3V3 >= 500mA

The parts I'm looking at are: TPS749xx (3A, 2%) TPS742xx (3A, 1%) and TPS747xx (500mA, 2%)

My question is: how is the voltage set for the fixed output variants? If the feedback resistors are simply brought on the die I suspect the tolerance will not be as tight as external 0.1% resistors. However, if the reference voltage is changed from 0.8V to match the target output voltage, then there are no feedback resistors to worry about...

Thanks,
Dave

  • 0
    TI__Guru 55940 points

    Hi Dave,

    The accuracy for fixed output versions of the device are governed by our accuracy spec in the Electrical Characteristics table.  We do not include external resistors in our accuracy spec as noted at the bottom of the table; however, we do include the internal components.  Either design for you mentioned for fixing the output would therefore be covered in our stated accuracy spec.

    Figure 4 of the TPS742xx datasheet indicates that we are using an internal resistor divider to fix the output for that family of device.

    Long story short, you do not need to worry about our internal feedback resistors in your accuracy calculation.

    Very Respectfully,

    Ryan

  • 0 in reply to Ryan Eslinger
    Prodigy 20 points

    Hi Ryan,

    Thanks for your response. My concern is that the accuracy spec in the Electrical Characteristics table was measured with an adjustable device with 0.8V output (Note 1).

    Can you confirm that a fixed output version (3.3V for example) will have the same accuracy spec as the adjustable part with 0.8V output?

    Thanks,
    Dave 

  • 0 in reply to david degraaf
    TI__Guru 55940 points

    Hi Dave,

    We currently only offer the adjustable versions through our website for these devices.

    Please contact support@ti.com for more information on ordering the fixed versions.

    Very Respectfully,

    Ryan

  • 0
    Intellectual 510 points

    david degraaf said:

    The parts I'm looking at are: TPS749xx (3A, 2%) TPS742xx (3A, 1%) and TPS747xx (500mA, 2%)

    Hello, Dave!

    TPS742xx 's Iout is not 3A, but 1,5A.

  • 0 in reply to Ryan Eslinger
    Intellectual 510 points

    Ryan Eslinger said:

    We currently only offer the adjustable versions through our website for these devices.

    Hello, Ryan!

    Do You mean, that the whole big family of TPS74xxx is now available only in adjustable versions?

  • 0 in reply to Sergei Vereskov
    TI__Guru 55940 points

    Hi Sergei,

    TPS74xxx is not considered a single family of devices.  The three families Dave mentioned in his first post, TPS749xx, TPS742xx, and TPS747xx currently only have the adjustable versions available from the web.

    Very Respectfully,

    Ryan