SBVS263B July   2017  – June 2025 TPS7A39

PRODUCTION DATA  

  1.   1
  2. 1 Features
  3. 2 Applications
  4. 3 Description
  5. 4 Pin Configuration and Functions
  6. 5 Specifications
    1. 5.1 Absolute Maximum Ratings
    2. 5.2 ESD Ratings
    3. 5.3 Recommended Operating Conditions
    4. 5.4 Thermal Information
    5. 5.5 Electrical Characteristics
    6. 5.6 Start-Up Characteristics
    7. 5.7 Timing Diagram
    8. 5.8 Typical Characteristics
  7. 6 Detailed Description
    1. 6.1 Overview
    2. 6.2 Functional Block Diagram
    3. 6.3 Feature Description
      1. 6.3.1 Voltage Regulation
        1. 6.3.1.1 DC Regulation
        2. 6.3.1.2 AC and Transient Response
      2. 6.3.2 User-Settable Buffered Reference
      3. 6.3.3 Active Discharge
      4. 6.3.4 System Start-Up Controls
        1. 6.3.4.1 Start-Up Tracking
        2. 6.3.4.2 Sequencing
          1. 6.3.4.2.1 Enable (EN)
          2. 6.3.4.2.2 Undervoltage Lockout (UVLO) Control
    4. 6.4 Device Functional Modes
      1. 6.4.1 Normal Operation
      2. 6.4.2 Dropout Operation
      3. 6.4.3 Disabled
  8. 7 Application and Implementation
    1. 7.1 Application Information
      1. 7.1.1  Setting the Output Voltages on Adjustable Devices
      2. 7.1.2  Capacitor Recommendations
      3. 7.1.3  Input and Output Capacitor (CINx and COUTx)
      4. 7.1.4  Feed-Forward Capacitor (CFFx)
      5. 7.1.5  Noise-Reduction and Soft-Start Capacitor (CNR/SS)
      6. 7.1.6  Buffered Reference Voltage
      7. 7.1.7  Overriding Internal Reference
      8. 7.1.8  Start-Up
        1. 7.1.8.1 Soft-Start Control (NR/SS)
          1. 7.1.8.1.1 In-Rush Current
        2. 7.1.8.2 Undervoltage Lockout (UVLOx) Control
      9. 7.1.9  AC and Transient Performance
        1. 7.1.9.1 Power-Supply Rejection Ratio (PSRR)
        2. 7.1.9.2 Channel-to-Channel Output Isolation and Crosstalk
        3. 7.1.9.3 Output Voltage Noise
        4. 7.1.9.4 Optimizing Noise and PSRR
        5. 7.1.9.5 Load Transient Response
      10. 7.1.10 DC Performance
        1. 7.1.10.1 Output Voltage Accuracy (VOUT x)
        2. 7.1.10.2 Dropout Voltage (VDO)
      11. 7.1.11 Reverse Current
      12. 7.1.12 Power Dissipation (PD)
        1. 7.1.12.1 Estimating Junction Temperature
    2. 7.2 Typical Applications
      1. 7.2.1 Design 1: Single-Ended to Differential Isolated Supply
        1. 7.2.1.1 Design Requirements
        2. 7.2.1.2 Detailed Design Procedure
          1. 7.2.1.2.1 Switcher Choice
          2. 7.2.1.2.2 Full Bridge Rectifier With Center-Tapped Transformer
          3. 7.2.1.2.3 Total Solution Efficiency
          4. 7.2.1.2.4 Feedback Resistor Selection
        3. 7.2.1.3 Application Curves
      2. 7.2.2 Design 2: Getting the Full Range of a SAR ADC
        1. 7.2.2.1 Design Requirements
        2. 7.2.2.2 Detailed Design Procedure
        3. 7.2.2.3 Detailed Design Description
          1. 7.2.2.3.1 Regulation of –0.2V
          2. 7.2.2.3.2 Feedback Resistor Selection
        4. 7.2.2.4 Application Curves
    3. 7.3 Power Supply Recommendations
    4. 7.4 Layout
      1. 7.4.1 Layout Guidelines
        1. 7.4.1.1 Board Layout Recommendations to Improve PSRR and Noise Performance
        2. 7.4.1.2 Package Mounting
      2. 7.4.2 Layout Example
  9. 8 Device and Documentation Support
    1. 8.1 Device Support
      1. 8.1.1 Development Support
        1. 8.1.1.1 Evaluation Modules
        2. 8.1.1.2 Spice Models
    2. 8.2 Documentation Support
      1. 8.2.1 Related Documentation
    3. 8.3 Receiving Notification of Documentation Updates
    4. 8.4 Support Resources
    5. 8.5 Trademarks
    6. 8.6 Electrostatic Discharge Caution
    7. 8.7 Glossary
  10. 9 Revision History
  11. 10Mechanical, Packaging, and Orderable Information

7.1.1 Setting the Output Voltages on Adjustable Devices

Figure 6-5 shows that each LDO resistor feedback network sets the output voltage. The positive LDO output voltage range is VNR/SS to 30V and the negative LDO output voltage range is 0V to –30V.

TPS7A39 Adjustable OperationFigure 7-1 Adjustable Operation

Equation 1 relates the values of R1P and R2P to VOUTP(NOM) and VNR/SS to set the positive output voltage. Equation 2 relates the values of R1N and R2N to VOUTN(NOM) and VNR/SS to set the negative output voltage.

The positive LDO is configured as a noninverting op amp, whereas the negative LDO is an inverting op amp.

Equation 1. VOUTP = VNR/SS × (1 + R1P / R2P)
Equation 2. VOUTN = VNR/SS × (–R1N / R2N)

Substituting VNR/SS with VFBP on the positive channel and VNR/SS with VBUF on the negative channel gives a more accurate relationship.

Equation 3 and Equation 2 are rearranged versions of Equation 1 and Equation 2, with the above substitutions made.

Equation 3. R1P = (VOUTP / VFBP – 1) × R2P
Equation 4. R1N = –(VOUTN × R2P) / VBUF

The minimum bias current through both feedback networks is 5µA to ensure accuracy.

For even tighter accuracy, take into account the input bias current into the error amplifiers (IFBP and IFBN) and use 0.1% resistors. Overriding the internal reference with a high accuracy external reference can also improve the accuracy of the device.

Table 7-1 and Table 7-2 show the resistor combinations for several common output voltages using commercially available, 1% tolerance resistors.

Table 7-1 Recommended Feedback-Resistor Values for the Positive LDO
TARGETED OUTPUT VOLTAGE (V) FEEDBACK RESISTOR VALUES(1) CALCULATED OUTPUT VOLTAGE (V)
R1P (kΩ) R2P (kΩ)
1.5 2.67 10.0 1.50
1.8 5.23 10.0 1.80
2.5 11.0 10.0 2.49
3.0 15.4 10.0 3.00
3.3 17.8 10.0 3.29
5.0 32.4 10.0 5.02
9.0 66.5 10.0 9.07
12.0 90.9 10.0 12.0
15.0 115 10.0 14.8
24.0 191 10.0 23.8
30.0 243 10.0 29.8
(1) R1P is connected from OUTP to FBP, R2P is connected from FBP to GND; see the Setting the Output Voltages on Adjustable Devices section.
Table 7-2 Recommended Feedback-Resistor Values for the Negative LDO
TARGETED OUTPUT VOLTAGE (V) FEEDBACK RESISTOR VALUES(1) CALCULATED OUTPUT VOLTAGE (V)
R1N (kΩ) R2N (kΩ)
-0.3 2.55 10.0 -0.303
-1.5 12.7 10.0 -1.51
-1.8 15.0 10.0 -1.78
-2.5 21.0 10.0 -2.49
-3.0 25.5 10.0 -3.03
-3.3 28.0 10.0 -3.33
-5.0 42.2 10.0 -5.04
-9.0 75.0 10.0 -8.91
-12.0 100 10.0 -11.9
-15.0 127 10.0 -15.1
-24.0 200 10.0 -23.8
-30.0 255 10.0 -30.3
(1) R1N is connected from OUTN to FBN, R2N is connected from FBN to BUF; see the Setting the Output Voltages on Adjustable Devices section.