LM317: adjustable positive-voltage linear regulator 

Description

The LM317 is an adjustable three-pin, positive-voltage linear regulator capable of supplying more than 1.5A over an output voltage range of 1.25V to 37V. The device requires only two external resistors to set the output voltage. The device features a typical line regulation of 0.01% and typical load regulation of 0.1%. The LM317 includes current limiting, thermal overload protection, and safe operating area protection. Overload protection remains functional even if the ADJUST pin is disconnected.

Typically, no capacitors are needed unless the device is situated more than 6 inches from the input filter capacitors. In that case, an input bypass is needed. Add an optional output capacitor to improve transient response. Bypass the adjustment pin to achieve very high ripple rejection ratios that are difficult to achieve with standard 3-pin regulators.

The regulator is floating and detects only the input-to-output differential voltage. Thus, supplies of several hundred volts are regulated as long as the maximum input-to-output differential is not exceeded. That is, avoid short-circuiting the output.

By connecting a fixed resistor between the adjustment pin and output, the LM317 is also able to be used as a precision current regulator. Supplies with electronic shutdown are achieved by clamping the adjustment terminal to ground, which programs the output to 1.25V where most loads draw little current.

Features:

• Output voltage range: 1.25V to 37V

• Output current: 1.5A

• Line regulation: 0.01%/V (typ)

• Load regulation: 0.1% (typ)

• Internal short-circuit current limiting

• Thermal overload protection

• Output safe-area compensation (new chip)

• PSRR: 80dB at 120Hz for CADJ = 10µF (new chip)

• Available Packages:

  • 4-pin, SOT-223 (DCY)

  • 3-pin, TO-263 (KTT)

  • 3-pin, TO-220 (KCS, KCT), legacy chip

Parameters

• Vin (max) (V): 40

• Vin (min) (V): 3

• Iout (max) (A): 1.5

• Output options: Adjustable Output, Fixed Output

• Vout (max) (V): 37

• Vout (min) (V): 1.25

• Noise (µVrms): 38

• PSRR at 100 KHz (dB): 38

• Iq (typ) (mA): 5

• Thermal resistance θJA (°C/W): 24

• Load capacitance (min) (µF): 0

• Regulated outputs (#): 1

• Accuracy (%):  5

• Dropout voltage (Vdo) (typ) (mV):  2000

• Operating temperature range (°C): 0 to 125