SLVS004I April   1979  – August 2016 TL317

PRODUCTION DATA.  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
  4. 4 Revision History
  5. 5 Pin Configuration and Functions
  6. 6 Specifications
    1. 6.1 Absolute Maximum Ratings
    2. 6.2 ESD Ratings
    3. 6.3 Recommended Operating Conditions
    4. 6.4 Thermal Information
    5. 6.5 Electrical Characteristics
    6. 6.6 Typical Characteristic
  7. 7 Detailed Description
    1. 7.1 Overview
    2. 7.2 Functional Block Diagrams
    3. 7.3 Feature Description
      1. 7.3.1 NPN Darlington Output Drive
      2. 7.3.2 Programmable Feedback
    4. 7.4 Device Functional Modes
      1. 7.4.1 Normal Operation
      2. 7.4.2 Operation With Low Input Voltage
      3. 7.4.3 Operation in Light Loads
  8. 8 Application and Implementation
    1. 8.1 Application Information
    2. 8.2 Typical Applications
      1. 8.2.1 Adjustable Voltage Regulator
        1. 8.2.1.1 Design Requirements
        2. 8.2.1.2 Detailed Design Procedure
        3. 8.2.1.3 Application Curve
      2. 8.2.2 0-V to 30-V Regulator Circuit
      3. 8.2.3 Regulator Circuit With Improved Ripple Rejection
      4. 8.2.4 Precision Current-Limiter Circuit
      5. 8.2.5 Tracking Preregulator Circuit
      6. 8.2.6 Slow-Turnon 15-V Regulator Circuit
      7. 8.2.7 50-mA Constant-Current Battery-Charger Circuit
      8. 8.2.8 Current-Limited 6-V Charger
      9. 8.2.9 High-Current Adjustable Regulator
  9. 9 Power Supply Recommendations
  10. 10Layout
    1. 10.1 Layout Guidelines
    2. 10.2 Layout Example
  11. 11Device and Documentation Support
    1. 11.1 Receiving Notification of Documentation Updates
    2. 11.2 Community Resources
    3. 11.3 Trademarks
    4. 11.4 Electrostatic Discharge Caution
    5. 11.5 Glossary
  12. 12Mechanical, Packaging, and Orderable Information

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8 Application and Implementation

NOTE

Information in the following applications sections is not part of the TI component specification, and TI does not warrant its accuracy or completeness. TI’s customers are responsible for determining suitability of components for their purposes. Customers should validate and test their design implementation to confirm system functionality.

8.1 Application Information

The flexibility of the TL317 allows it to be configured to take on many different functions in DC power applications.

8.2 Typical Applications

8.2.1 Adjustable Voltage Regulator

TL317 app1_lvs004.gif Figure 4. Adjustable Voltage Regulator

8.2.1.1 Design Requirements

  • R1 and R2 are required to set the output voltage.
  • C1 is recommended, particularly if the regulator is not in close proximity to the power-supply filter capacitors. A 0.1-µF ceramic or 1-µF tantalum capacitor provides sufficient bypassing for most applications, especially when adjustment and output capacitors are used.
  • Use of an output capacitor, C2, improves transient response, but is optional.

8.2.1.2 Detailed Design Procedure

VO is calculated as shown in Equation 1. IADJ is typically 50 µA and negligible in most applications.

Power dissipation for linear regulators is calculated as shown in Equation 2. IADJ is typically 50 µA and negligible in most applications, so a typical way to calculate power dissipation for linear regulators is simplified to Equation 3.

Equation 1. VO = VREF (1 + R2 / R1) + (IADJ × R2)
Equation 2. P = (VI - VO) × IO + (VI - VADJ) × IADJ
Equation 3. P = (VI - VO) × IO

8.2.1.3 Application Curve

TL317 adjustment_voltage.gif Figure 5. Line Regulation

8.2.2 0-V to 30-V Regulator Circuit

VO is calculated as shown in Equation 4, where Vref equals the difference between OUTPUT and ADJUSTMENT voltages (approximately 1.25 V).

Equation 4. TL317 lm317l_appeqn.gif
TL317 app2_lvs004.gif Figure 6. 0-V to 30-V Regulator Circuit Schematic

8.2.3 Regulator Circuit With Improved Ripple Rejection

  • Protection diode D1 is recommended if C2 is used. The diode provides a low-impedance discharge path to prevent the capacitor from discharging into the output of the regulator
  • Use of an output capacitor, C2, improves transient response, but is optional.
TL317 app3_lvs004.gif Figure 7. Regulator Circuit With Improved Ripple Rejection Schematic

8.2.4 Precision Current-Limiter Circuit

The use of the TL317 in this configuration limits the output current to Ilimit shown in Figure 8.

TL317 app4_lvs004.gif Figure 8. Precision Current-Limiter Circuit

8.2.5 Tracking Preregulator Circuit

This application keeps a constant voltage across the second TL317 in the circuit.

TL317 app5_lvs004.gif Figure 9. Tracking Preregulator Circuit Schematic

8.2.6 Slow-Turnon 15-V Regulator Circuit

The capacitor C1, in combination with the PNP transistor, helps the circuit to slowly start supplying voltage. In the beginning, the capacitor is not charged. Therefore, output voltage starts at VC1+ VBE + 1.25 V = 0 V + 0.65 V + 1.25 V = 1.9 V. As the capacitor voltage rises, VOUT also rises at the same rate. When the output voltage reaches the value determined by R1 and R2, the PNP is turned off.

TL317 app6_lvs004.gif Figure 10. Slow-Turnon 15-V Regulator Circuit Schematic

8.2.7 50-mA Constant-Current Battery-Charger Circuit

The current limit operation mode can be used to trickle charge a battery at a fixed current. ICHG = 1.25 V / 24 Ω. VI must be greater than VBAT + 4.25 V (1.25 V [VREF] + 3 V [headroom]).

Power dissipation through resistor R1 is calculated as shown in Equation 5, so a resistor with the appropriate power rating must be chosen for this application.

Equation 5. P(R1) = IO2 × R1[Ω]
TL317 app7_lvs004.gif Figure 11. 50-mA Constant-Current Battery-Charger Circuit

8.2.8 Current-Limited 6-V Charger

As the charge current increases, the voltage at the bottom resistor increases until the NPN starts sinking current from the adjustment pin. The voltage at the adjustment pin drops, and consequently the output voltage decreases until the NPN stops conducting.

TL317 app8_lvs004.gif Figure 12. Current-Limited 6-V Charger Schematic

8.2.9 High-Current Adjustable Regulator

The NPNs at the top of the schematic allow higher currents at VOUT than the LM317 can provide, while still keeping the output voltage at levels determined by the adjustment pin resistor divider of the LM317.

TL317 app9_lvs004.gif
A. Minimum load current is 30 mA.
B. Optional capacitor improves ripples rejection.
Figure 13. High-Current Adjustable Regulator Schematic