JAJSBB9C May   1998  – December 2016 LM138 , LM338

PRODUCTION DATA.  

  1. 特長
  2. アプリケーション
  3. 概要
  4. 改訂履歴
  5. Pin Configuration and Functions
  6. Specifications
    1. 6.1 Absolute Maximum Ratings
    2. 6.2 Recommended Operating Conditions
    3. 6.3 Thermal Information
    4. 6.4 Electrical Characteristics: LM138
    5. 6.5 Electrical Characteristics: LM338
    6. 6.6 Typical Characteristics
  7. Detailed Description
    1. 7.1 Overview
    2. 7.2 Functional Block Diagram
    3. 7.3 Feature Description
      1. 7.3.1 NPN Darlington Output Drive
      2. 7.3.2 Overload Block
      3. 7.3.3 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 at Light Loads
      4. 7.4.4 Operation in Self Protection
  8. Application and Implementation
    1. 8.1 Application Information
    2. 8.2 Typical Applications
      1. 8.2.1 Constant 5-V Regulator
        1. 8.2.1.1 Design Requirements
        2. 8.2.1.2 Detailed Design Procedure
          1. 8.2.1.2.1 External Capacitors
          2. 8.2.1.2.2 Load Regulation
          3. 8.2.1.2.3 Protection Diodes
        3. 8.2.1.3 Application Curves
    3. 8.3 System Examples
  9. Power Supply Recommendations
  10. 10Layout
    1. 10.1 Layout Guidelines
    2. 10.2 Layout Example
  11. 11デバイスおよびドキュメントのサポート
    1. 11.1 ドキュメントの更新通知を受け取る方法
    2. 11.2 関連リンク
    3. 11.3 コミュニティ・リソース
    4. 11.4 商標
    5. 11.5 静電気放電に関する注意事項
    6. 11.6 用語集
  12. 12メカニカル、パッケージ、および注文情報

パッケージ・オプション

メカニカル・データ(パッケージ|ピン)
サーマルパッド・メカニカル・データ
発注情報

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.

Application Information

In operation, the LM138 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 with Equation 1.

Equation 1. LM138 LM338 00906047.gif
LM138 LM338 00906006.gif Figure 15. Typical Application Circuit

Because the 50-µA current from the adjustment terminal represents an error term, the LM138 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 rises.

Typical Applications

Constant 5-V Regulator

LM138 LM338 typ_app_circuit_SNVS711.gif Figure 16. Constant 5-V Regulator

Design Requirements

R1: Because the LM138 produces a typical 1.24 V potential between the OUTPUT and ADJUST pins, placing a 270-Ω resistor between them causes 4.6 mA to flow through R1 and R2.

R2: To achieve a 5-V output, the sum of the voltages across R1 and R2 must equal 5 V. Therefore, Vr2 must equal 3.76 V when 4.6 mA is flowing through it. R2 = Vr2 / I = 3.76 V / 4.6 mA = ~820 Ω.

CIN: 0.1 µF of input capacitance helps filter out unwanted noise, especially if the regulator is located far from the power supply filter capacitors.

COUT: The regulator is stable without any output capacitance, but adding a 1-µF capacitor improves the transient response.

CADJ: A 10-µF capacitor bypassing the ADJUST pin to ground improves the regulators ripple rejection.

D1: Protection diode D1 is recommended if COUT is used. The diode provides a low-impedance discharge path to prevent the capacitor from discharging into the output of the regulator (see Protection Diodes).

D2: Protection diode D2 is recommended if CADJ is used. The diode provides a low-impedance discharge path to prevent the capacitor from discharging into the output of the regulator (see Protection Diodes).

Table 1 lists the design parameters for this typical application.

Table 1. Design Parameters

PARAMETER VALUE
Feedback resistor 1 (R1) 270 Ω
Feedback resistor 2 (R2) 820 Ω
Input capacitor (CIN) 0.1 µF
Output capacitor (COUT) 1 µF
Adjust capacitor(CADJ) 10 µF

Detailed Design Procedure

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 eliminate the possibility of problems.

The adjustment terminal can be bypassed to ground on the LM138 to improve ripple rejection. This bypass capacitor prevents ripple from being amplified as the output voltage is increased. With a 10-µF bypass capacitor, 75-dB ripple rejection is obtainable at any output level. Increases over 20 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 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, 0.01-µF disc may seem to work better than a 0.1-µF disc as a bypass.

Although the LM138 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 insures stability.

Load Regulation

The LM138 is capable of providing extremely good load regulation but a few precautions are needed to obtain maximum performance. The current set resistor connected between the adjustment terminal and the output terminal (usually 240 Ω) must be tied directly to the output of the regulator (case) rather than near the load. This eliminates line drops from appearing effectively in series with the reference and degrading regulation. For example, a 15-V regulator with 0.05-Ω resistance between the regulator and load has a load regulation due to line resistance of 0.05 Ω × IL. If the set resistor is connected near the load, the effective line resistance is 0.05 Ω (1 + R2/R1) or in this case, 11.5 times worse.

Figure 17 shows the effect of resistance between the regulator and 240-Ω set resistor.

LM138 LM338 00906007.gif Figure 17. 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 2 separate leads to the case. The ground of R2 can be returned near the ground of the load to provide remote ground sensing and improve load regulation.

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 20-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 discharges 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 LM138 this discharge path is through a large junction that is able to sustain 25-A surge with no problem. This is not true of other types of positive regulators. For output capacitors of 100 µF or less at output of 15 V 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 LM138 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 18 shows an LM138 with protection diodes included for use with outputs greater than 25 V and high values of output capacitance.

LM138 LM338 00906008.gif LM138 LM338 00906048.png
D1 protects against C1
D2 protects against C2
Figure 18. Regulator With Protection Diodes

Application Curves

LM138 LM338 Start UP1.png Figure 19. Regulator Start-Up
LM138 LM338 Start UP4.png Figure 21. Regulator Response to Load Step
LM138 LM338 Start UP2.png Figure 20. Regulator Shutdown

System Examples

LM138 LM338 00906003.gif Figure 22. Regulator and Voltage Reference
LM138 LM338 00906010.gif
Full output current not available at high input-output voltages
†Optional—improves transient response. Output capacitors in the range of 1 µF to 1000 µF of aluminum or tantalum electrolytic are commonly used to provide improved output impedance and rejection of transients.
*Needed if device is more than 6 inches from filter capacitors.

**R1 = 240 Ω for LM138. R1, R2 as an assembly can be ordered from Bourns:
MIL part no. 7105A-AT2-502
COMM part no. 7105A-AT7-502
Figure 24. Temperature Controller
LM138 LM338 00906013.gif Figure 26. Slow Turnon 15-V Regulator
LM138 LM338 00906015.gif Figure 28. High Stability 10-V Regulator
LM138 LM338 00906017.gif
* Minimum load—100 mA
Figure 30. 15-A Regulator
LM138 LM338 00906011.gif Figure 32. Light Controller
LM138 LM338 00906020.gif Figure 34. 12-V Battery Charger
LM138 LM338 00906022.gif Figure 36. Precision Current Limiter
LM138 LM338 00906024.gif Figure 38. Tracking Preregulator

LM138 LM338 00906027.gif
AV = 1, RF = 10k, CF = 100 pF
AV = 10, RF = 100k, CF = 10 pF
Bandwidth ≥ 100 kHz
Distortion ≤ 0.1%
Figure 40. Power Amplifier
LM138 LM338 00906026.gif Figure 42. Adjustable 15-A Regulator
LM138 LM338 00906002.gif
* Minimum load—100 mA
Figure 44. 10-A Regulator
LM138 LM338 00906001.gif Figure 23. 1.2-V to 25-V Adjustable Regulator
LM138 LM338 00906012.gif
* Adjust for 3.75 across R1
Figure 25. Precision Power Regulator With
Low Temperature Coefficient
LM138 LM338 00906014.gif
†Solid tantalum
*Discharges C1 if output is shorted to ground
**R1 = 240 Ω for LM138
Figure 27. Adjustable Regulator With
Improved Ripple Rejection
LM138 LM338 00906016.gif
*Sets maximum VOUT
**R1 = 240 Ω for LM138
Figure 29. Digitally Selected Outputs
LM138 LM338 00906018.gif
** Minimum output ≈ 1.2 V
Figure 31. 5-V Logic Regulator With
Electronic Shutdown**
LM138 LM338 00906019.gif
* R1 = 240 Ω, R2 = 5k for LM138
Full output current not available at high input-output voltages
Figure 33. 0 to 22-V Regulator
LM138 LM338 00906021.gif Figure 35. Adjustable Current Regulator
LM138 LM338 00906023.gif Figure 37. 5-A Current Regulator
LM138 LM338 00906025.gif
† Minimum load—10 mA
* All outputs within ±100 mV
Figure 39. Adjusting Multiple On-Card Regulators With Single Control*
LM138 LM338 00906028.gif

Use of RS allows low charging rates with fully charged battery.
**The 1000 µF is recommended to filter out input transients

Use of RS allows low charging rates with fully charged battery.
**The 1000 µF is recommended to filter out input transients
Figure 41. Simple 12-V Battery Charger
LM138 LM338 00906029.gif
* Set max charge current to 3 A
** THE 1000 µF is recommended to filter out input transients.
Figure 43. Current Limited 6-V Charger