SLCS144F July 2004 – December 2024 LM317L
PRODUCTION DATA
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The LM317L is a 100mA linear regulator with high voltage tolerance up to 37V. The device has a feedback voltage that is relative to the output instead of ground. This ungrounded design allows the LM317L device to have superior line and load regulation. This design also allows the LM317L device to be used as a current source or current sink using a single resistor. Any output voltage from 1.25V to 32V can be obtained by using two resistors. The bias current of the device, up to 2.5mA, flows to the output; this current must be used by the load or the feedback resistors. The power dissipation is the product of pass transistor voltage and current, which is calculated as shown in Equation 1.
The application heat sink must be able to absorb the power calculated in Equation 1.
In addition to higher performance than fixed regulators, this regulator offers full overload protection, available only in integrated circuits. Included on the chip are current-limiting and thermal-overload protection. All overload-protection circuitry remains fully functional even when ADJUSTMENT is disconnected. Normally, no capacitors are needed unless the device is situated far from the input filter capacitors, in which case an input bypass is needed. An optional output capacitor can be added to improve transient response. ADJUSTMENT can be bypassed to achieve very high ripple rejection, which is difficult to achieve with standard three-terminal regulators.
In addition to replacing fixed regulators, the LM317L regulator is useful in a wide variety of other applications. Because the regulator is floating and observes only the input-to-output differential voltage, supplies of several hundred volts can be regulated as long as the maximum input-to-output differential is not exceeded. The primary application is that of a programmable output regulator, but by connecting a fixed resistor between ADJUSTMENT and OUTPUT, this device can be used as a precision current regulator. Supplies with electronic shutdown can be achieved by clamping ADJUSTMENT to ground, programming the output to 1.25V, where most loads draw little current.
The LM317LC is characterized for operation over the virtual junction temperature range of 0°C to 125°C. The LM317LI is characterized for operation over the virtual junction temperature range of –40°C to 125°C.