LM217L datasheet(9/18 Pages) STMICROELECTRONICS

9 / 18 page

LM217L/LM317L

Application information

9/18

Application information

The LM317L provides an internal reference voltage of 1.25V between the output and

adjustments terminals. This is used to set a constant current flow across an external resistor

divider (see Figure 4.), giving an output voltage VO of:

VO = VREF (1 + R2/R1) + IADJ R2

The device was designed to minimize the term IADJ (100µA max) and to maintain it very

constant with line and load changes. Usually, the error term IADJ × R2 can be neglected. To

obtain the previous requirement, all the regulator quiescent current is returned to the output

terminal, imposing a minimum load current condition. If the load is insufficient, the output

voltage will rise.

Since the LM317L is a floating regulator and "sees" only the input-to-output differential

voltage, supplies of very high voltage with respect to ground can be regulated as long as the

maximum input-to-output differential is not exceeded. Furthermore, programmable regulator

are easily obtainable and, by connecting a fixed resistor between the adjustment and output,

the device can be used as a precision current regulator. In order to optimize the load

regulation, the current set resistor R1 (see Figure 4.) should be tied as close as possible to

the regulator, while the ground terminal of R2 should be near the ground of the load to

provide remote ground sensing.

LM217L 数据表(PDF) 9 Page - STMicroelectronics