LM317M STMicroelectronics, LM317M Datasheet - Page 9

• Manufacturer Part Number: LM317M
• Description: Medium current 1.2 to 37 V adjustable voltage regulator
• Manufacturer: STMicroelectronics

Specifications of LM317M

• Output Voltage Range: 1.2 to 37V

6
6.1
6.2
6.3
Application information
The LM217M/LM317M provide an internal reference voltage of 1.25 V between the output
and adjustment terminals. These devices are used to set a constant current flow across an
external resistor divider (see
R
The devices were designed to minimize the term I
constant in line and load changes. Usually, the error term I
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 LM217M/LM317M devices are floating regulators and "see" 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 regulators are easily obtained and, by connecting a fixed resistor between
the adjustment and output, the devices can be used as a precision current regulator. In
order to optimize the load regulation, the current set resistor R
tied as close as possible to the regulator, while the ground terminal of R
ground of the load to provide remote ground sensing.
External capacitors
Normally no capacitors are needed unless the devices are situated far from the input filter
capacitors; in which case an input bypass is needed.
A 0.1 µF disc or 1 µF tantalum input bypass capacitor (C
sensitivity to input line impedance.
The adjustment terminal may be bypassed to ground to improve ripple rejection. This
capacitor (C
10 µF capacitor should improve ripple rejection of about 80 dB at 120 Hz in a 10 V
application.
Although the LM217M/LM317M devices are stable with no output capacitance like any
feedback circuit, certain values of external capacitance can cause excessive ringing. An
output capacitance (C
capacitor on the output swamps this effect and insures stability.
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.
Figure 6
voltages in excess of 25 V or high capacitance values (C
prevents C
of diodes D1 and D2 prevents C
output short-circuit.
Start-up block
It’s not guaranteed the Re-Boot of the device when the junction temperature is over 85 °C.
1
) + I
ADJ
shows the LM217M/LM317M with the recommended protection diodes for output
R
3
2.
ADJ
from discharging through the IC during an input short-circuit. The combination
) prevents ripple from being amplified as the output voltage is increased. A
O
) in the form of a 1 µF tantalum or 25 µF aluminium electrolytic
(Figure
Figure
(Figure
2
from discharging through the regulator during an input or
6), giving an output voltage V
8)
8)
ADJ
(100 µA max) and to maintain it very
I
3
) is recommended to reduce the
> 25 µF, C
ADJ
× R
1
(see
O
2
of: V
can be neglected. To
2
Figure
> 10 µF). Diode D1
2
O
should be near the
= V
6) should be
REF
(1 + R
9/21
2
/