SNVS773D April   2000  – September 2015 LM117HV , LM317HV

PRODUCTION DATA.  

  1. Features
  2. Applications
  3. Description
  4. Revision History
  5. Device Comparison Table
  6. Pin Configuration and Functions
  7. Specifications
    1. 7.1 Absolute Maximum Ratings
    2. 7.2 ESD Ratings
    3. 7.3 Recommended Operating Conditions
    4. 7.4 Thermal Information
    5. 7.5 Electrical Characteristics
    6. 7.6 Typical Characteristics
  8. Detailed Description
    1. 8.1 Overview
    2. 8.2 Functional Block Diagram
    3. 8.3 Feature Description
      1. 8.3.1 Load Regulation
      2. 8.3.2 Current Limit
    4. 8.4 Device Functional Modes
      1. 8.4.1 External Capacitors
      2. 8.4.2 Protection Diodes
  9. Application and Implementation
    1. 9.1 Application Information
    2. 9.2 Typical Applications
      1. 9.2.1  1.25-V to 45-V High Voltage Adjustable Regulator
        1. 9.2.1.1 Design Requirements
        2. 9.2.1.2 Detailed Design Procedure
        3. 9.2.1.3 Application Curve
      2. 9.2.2  Digitally Selected Outputs
      3. 9.2.3  Logic Regulator (5-V) With Electronic Shutdown
      4. 9.2.4  Slow Turnon 15-V Regulator
      5. 9.2.5  Adjustable Regulator With Improved Ripple Rejection
      6. 9.2.6  High Stability 10-V Regulator
      7. 9.2.7  High Current Adjustable Regulator
      8. 9.2.8  Emitter Follower Current Amplifier
      9. 9.2.9  1-A Current Regulator
      10. 9.2.10 Common Emitter Amplifier
      11. 9.2.11 Low-Cost, 3-A Switching Regulator
      12. 9.2.12 Adjustable Multiple On-Card Regulators With Single Control
      13. 9.2.13 AC Voltage Regulator
      14. 9.2.14 12-V Battery Charger
      15. 9.2.15 Adjustable 4-A Regulator
      16. 9.2.16 Current Limited 6-V Charger
  10. 10Power Supply Recommendations
  11. 11Layout
    1. 11.1 Layout Guidelines
    2. 11.2 Layout Example
  12. 12Device and Documentation Support
    1. 12.1 Related Links
    2. 12.2 Community Resources
    3. 12.3 Trademarks
    4. 12.4 Electrostatic Discharge Caution
    5. 12.5 Glossary
  13. 13Mechanical, Packaging, and Orderable Information

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8 Detailed Description

8.1 Overview

In operation, the LM317HV develops a nominal 1.25-V reference voltage, VREF, between the output and adjustment terminal. The reference voltage is impressed across program resistor R1 and, since the voltage is constant, a constant current I1 then flows through the output set resistor R2, giving an output voltage calculated by Equation 1:

Equation 1. LM117HV LM317HV eq2_VOUT_SNVS773.gif
LM117HV LM317HV 00906205.png Figure 13. Adjustable VOUT Through R1 and R2

Because the 100-μA current from the adjustment terminal represents an error term, the LM317HV was designed to minimize IADJ and make it very constant with line and load changes. To do this, all quiescent operating current is returned to the output establishing a minimum load current requirement. If there is insufficient load on the output, the output will rise.

8.2 Functional Block Diagram

LM117HV LM317HV 00906208.png

8.3 Feature Description

8.3.1 Load Regulation

The LM317HV is capable of providing extremely good load regulation but a few precautions are needed to obtain maximum performance. The current set resistor, R1, should be connected near the output terminal of the regulator rather than near the load. If R1 is placed too far from the output terminal, then the increased trace resistance, RS, will cause an error voltage drop in the adjustment loop and degrade load regulation performance. Therefore, R1 should be placed as close as possible to the output terminal to minimize RS and maximize load regulation performance.

Figure 14 shows the effect of the trace resistance, RS, when R1 is placed far from the output terminal of the regulator. It is clear that RS will cause an error voltage drop especially during higher current loads, so it is important to minimize the RS trace resistance by keeping R1 close to the regulator output terminal.

LM117HV LM317HV 00906206.png Figure 14. Regulator With Line Resistance in Output Lead

With the TO-3 package, it is easy to minimize the resistance from the case to the set resistor, by using two separate leads to the case. However, with the TO-39 package, take care to minimize the wire length of the output lead. The ground of R2 can be returned near the ground of the load to provide remote ground sensing and improve load regulation.

8.3.2 Current Limit

Internal current limit will be activated whenever the output current exceeds the limit indicated in Typical Characteristics. However, if the regulators differential voltage exceeds the absolute maximum rating of 60 V during a short-circuit condition (for example: VIN ≥ 60 V, VOUT = 0 V), internal junctions in the regulator may break down and the device may be damaged or fail. Failure modes range from an apparent open or short from input to output of the regulator, to a destroyed package (most common with the TO-220 package). To protect the regulator, the user is advised to be aware of voltages that may be applied to the regulator during fault conditions and to avoid violating the Absolute Maximum Ratings.

8.4 Device Functional Modes

8.4.1 External Capacitors

An input bypass capacitor is recommended. A 0.1-μF disc or 1-μF solid tantalum on the input is suitable input bypassing for almost all applications. The device is more sensitive to the absence of input bypassing when adjustment or output capacitors are used but the above values will eliminate the possibility of problems.

The adjustment terminal can be bypassed to ground on the LM317HV to improve ripple rejection. This bypass capacitor prevents ripple from being amplified as the output voltage is increased. With a 10-μF bypass capacitor the 80-dB ripple rejection is obtainable at any output level. Increases over 10 μF do not appreciably improve the ripple rejection at frequencies above 120 Hz. If the bypass capacitor is used, it is sometimes necessary to include protection diodes to prevent the capacitor from discharging through internal low current paths and damaging the device.

In general, the best type of capacitors to use are solid tantalum. Solid tantalum capacitors have low impedance even at high frequencies. Depending upon capacitor construction, it takes about 25 μF in aluminum electrolytic to equal 1 μF of solid tantalum at high frequencies. Ceramic capacitors are also good at high frequencies, but some types have a large decrease in capacitance at frequencies around 0.5 MHz. For this reason, a 0.01-μF disc may seem to work better than a 0.1-μF disc as a bypass.

Although the LM317HV is stable with no output capacitors, like any feedback circuit, certain values of external capacitance can cause excessive ringing. This occurs with values between 500 pF and 5000 pF. A 1-μF solid tantalum (or 25-μF aluminum electrolytic) on the output swamps this effect and ensures stability. Any increase of load capacitance larger than 10 μF will merely improve the loop stability and output impedance.

8.4.2 Protection Diodes

When external capacitors are used with any IC regulator it is sometimes necessary to add protection diodes to prevent the capacitors from discharging through low current points into the regulator. Most 10-μF capacitors have low enough internal series resistance to deliver 20-A spikes when shorted. Although the surge is short, there is enough energy to damage parts of the IC.

When an output capacitor is connected to a regulator and the input is shorted, the output capacitor will discharge into the output of the regulator. The discharge current depends on the value of the capacitor, the output voltage of the regulator, and the rate of decrease of VIN. In the LM317HV, this discharge path is through a large junction that is able to sustain 15-A surge with no problem. This is not true of other types of positive regulators. For output capacitors of 25 μF or less, there is no need to use diodes.

The bypass capacitor on the adjustment terminal can discharge through a low current junction. Discharge occurs when either the input or output is shorted. Internal to the LM317HV is a 50-Ω resistor which limits the peak discharge current. No protection is needed for output voltages of 25 V or less and 10-μF capacitance. Figure 15 shows an LM317HV with protection diodes included for use with outputs greater than 25 V and high values of output capacitance.

LM117HV LM317HV 00906207.png
LM117HV LM317HV eq1_VOUT_SNVS773.gif
D1 protects against C1
D2 protects against C2
Figure 15. Regulator With Protection Diodes