SBVA093 December   2022 LP2992 , TPS786 , TPS7A30 , TPS7A3001-EP , TPS7A33 , TPS7A39 , TPS7A4501-SP , TPS7A47 , TPS7A47-Q1 , TPS7A4701-EP , TPS7A49 , TPS7A52 , TPS7A52-Q1 , TPS7A53 , TPS7A53-Q1 , TPS7A53A-Q1 , TPS7A53B , TPS7A54 , TPS7A54-Q1 , TPS7A57 , TPS7A7100 , TPS7A7200 , TPS7A7300 , TPS7A80 , TPS7A8300 , TPS7A83A , TPS7A84 , TPS7A84A , TPS7A85 , TPS7A85A , TPS7A87 , TPS7A89 , TPS7A90 , TPS7A91 , TPS7A92 , TPS7A94 , TPS7A96 , TPS7B7702-Q1 , TPS7H1111-SEP , TPS7H1111-SP , TPS7H1210-SEP

 

  1.   Abstract
  2.   Trademarks
  3. 1Introduction
  4. 2Comprehensive Review of Error in LDO's
    1. 2.1 Commentary on Real World Error Voltage (VE) in Single LDO's
      1. 2.1.1 VREF Pin
      2. 2.1.2 VFB Pin
  5. 3Current Sharing and Load Voltage Analysis for n Parallel LDO's
    1. 3.1 Commentary on Parallel LDO's in Real World Applications
  6. 4Ballast Resistor Design and Analysis
    1. 4.1 Selecting the Ballast Resistor Value
    2. 4.2 PCB Ballast Resistor Design vs. Discrete Ballast Resistance
  7. 5Impacts and Opportunities of PCB Parasitic Impedance
  8. 6Design Examples
    1. 6.1 TPS7A57
    2. 6.2 TPS7A47xx
  9. 7Conclusion
  10. 8References

2.1.1 VREF Pin

While the reference voltage is most often derived from a precision voltage source VREF, in some voltage regulators, a precision current source IREF flows into a resistor to set the VREF voltage (Figure 2-1(c)). In converters where IREF and / or VREF is internal to the device, IBIAS is included in the tolerance of IREF, and VOS is included in the tolerance of VREF.

If the VREF pin is accessible to the designer with the intent that VREF is generated externally, VOS of the internal error amplifier must be known and may be located in the LDO data sheet. Although the term (∆VREF + ∆VOS) is rarely included in LDO's, when external resistors are used to program VOUT this information is needed to complete (Equation 2). Texas Instruments has developed a new down-loadable software tool with this information included for some of our LDOs see reference [7]. In the event that a TI LDO does not have this information in the data sheet or the software tool, submit a request for the information on our E2E forum.