This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

TPS7H1101A-SP: Iground or Iq

Part Number: TPS7H1101A-SP

I noticed that in the app note slyy151a (LDO basics), page 11, eqn. 1, Iq is used for power dissipation consumed and Iground (page 8, eqn1) is used for Pd in the thermal power dissipation calculation.  Iq = 8mA and Iground = 16mA, so the difference between the two is large.  Why are different currents used for these two calculations?  Why are these currents so large?  The commercial parts use a lot less current, on the order of a 100uA.

  • Susan,

    I am uncertain where the quoted values of 8ma for Iq, and 16ma for Iground come from.

    However, Iq, and Iground are essentially the same parameter, but Iq is defined with no load Iout = 0.

    The Pd equation for the TPS7H1101A can replace Iground for Iq with respect to the current loading condition being evaluated.  If Iout =0, then Iground = Iq.

    The predominant reason that the TPS7H1101A-SP has higher quiescent or ground current than other commercial LDOs is due to its more robust design intended to minimize single event effects (SEE) from heavy ion induced radiation.  Increasing the biasing allows the circuit to mitigate internal transients induced from these events more effectively.

    Reply back if you would like further clarification.

    If it does answers your question, please click this resolved my question.
    Regards,
    Wade

  • The values I gave you for Iq and Iground are on page 8 of the TPS7H1101A-SP data sheet.  I have copied them into the window below.  I was really hoping that the power dissipated wasn't 16mA*(Vin-Vout), this is huge.  8mA*(Vin-Vout) is bad enough.  Iground is twice the current of Iq ( 16mA vs. 8mA)?

  • Susan,

    Sorry, I was confused by the 8ma.  8ma is not in the table.

    However, the prior statements are valid.  Iq and Iground are the same current.  Iq only defines the no load case.  Iground is across all load currents.

    The max iground of 16ma is for a 2A Iout condition.  At light loads, Iground will decrease becoming closer to Iq.  The typical plot for figure 6-3 shows this relationship with a typical drop from 2A to no load of about 4mA

    Unfortunately, part of the trade off of designing for radiation tolerance is higher ground current.

    If you provide more of your constraints, I can possibly help you find an alternate LDO.   However, all of the radiation hardened LDOs will have higher ground currents due to the nature of their design.

    Regards,

    Wade

  • I just realized, I picked 8mA, because it was between the 7 and 10mA stated for Iq in the data sheet.  Sorry for the confusion!  Figure 6-3 works.  Thanks!