SLVAFX0 October   2024 TLV702 , TLV703 , TLV755P , TPS74401 , TPS7A13 , TPS7A14 , TPS7A20 , TPS7A21 , TPS7A49 , TPS7A52 , TPS7A53 , TPS7A53B , TPS7A54 , TPS7A57 , TPS7A74 , TPS7A83A , TPS7A84A , TPS7A85A , TPS7A91 , TPS7A92 , TPS7A94 , TPS7A96 , TPS7H1111-SP

 

  1.   1
  2.   Abstract
  3.   Trademarks
  4. 1Introduction to linear regulator turn-on time
  5. 2What impacts the LDO rise time?
    1. 2.1 Simple Use Cases
      1. 2.1.1 Case 1: LDO with an NR filter but without CFF capacitance
      2. 2.1.2 Case 2: NR filter with a CFF capacitance
      3. 2.1.3 Fast-charge circuitry
      4. 2.1.4 Non-ideal LDO behavior
        1. 2.1.4.1 Applied voltage bias
        2. 2.1.4.2 Fast charge current tolerance
        3. 2.1.4.3 Internal error amplifier offset voltage
        4. 2.1.4.4 Temperature impacts the fast-charge current source
        5. 2.1.4.5 Error amplifier common mode voltage
        6. 2.1.4.6 Reference voltage (VREF) ramp time dominates the turn-on time
        7. 2.1.4.7 Start-up during dropout mode
        8. 2.1.4.8 Large values of COUT induce internal current limit
        9. 2.1.4.9 Limitations of large-signal LDO bandwidth
    2. 2.2 Specific Use Cases and Examples
      1. 2.2.1 Case 3: Precision voltage reference with RNR/SS and parallel IFC fast charge
      2. 2.2.2 Case 4: Precision voltage reference with IFC fast charge and no RNR/SS
      3. 2.2.3 Case 5: Precision current reference
      4. 2.2.4 Case 6: Soft-start timing
  6. 3System Considerations
    1. 3.1 Inrush current calculation
    2. 3.2 Inrush current analysis
    3. 3.3 Maximum slew rate
  7. 4LDO regulators referenced in this paper
  8. 5Conclusion
  9. 6References

2.1.4.5 Error amplifier common mode voltage

The non-ideal common mode voltage (VCM) of the internal error amplifier may induce a sudden step in the LDO regulator turn-on response in older devices. This response is not as pronounced in most modern LDO regulators. LDO regulators that include this induced step response offer a shorter ramp time and longer delay time. The ramp rate of the small voltage step during the initial turn on is a function of the LDO bandwidth, which is different for each LDO regulator. To obtain this ramp rate, it is best to capture a measurement from an EVM after applying the system load. This measurement provides a more accurate evaluation of the device bandwidth.

TPS7A20, TPS7A21, TPS7A13, TPS7A14, TPS7A49, TPS7A91, TPS7A92, TLV702, TLV703, TLV755P, TPS7A52, TPS7A53, TPS7A53B, TPS7A54, TPS7A83A, TPS7A84A, TPS7A85A, TPS7A57, TPS7A94, TPS7A96, TPS7H1111-SP, TPS74401, TPS7A74, TPS74701, TPS74801, TPS74901 VCM can affect the turn-on time Figure 2-9 VCM can affect the turn-on time