3A L.D.O. VOLTAGE REGULATOR (Adjustable & Fixed)
LM1085
APPLICATION INFORMATION
The LM1085 series of adjustable and fixed regulators are easy to use and have all the protection features
expected in high performance voltage regulators : short circuit protection and thermal shut-down. Pin compatible
with older three terminal adjustable regulators, these devices offer the advantage of a lower dropout voltage,
more precies reference tolerance and improved reference stability with temperature.
STABILITY
The circuit design used in the LM1085 series requires the use of an output capacitor as part of the device
frequency compensation.
The addition of 150uF aluminum electrolytic or a 22uF solid tantalum on the output will ensure stability for
all operating conditions. When the adjustment terminal is bypassed with a capacitor to improve the ripple
rejection, the requirement for an output capacitor increases. The value of 22uF tantalum or 150uF aluminum
covers all cases of bypassing the adjustment terminal. Without bypassing the adjustment terminal smaller
capacitors can be used with equally good results.
To ensure good transient response with heavy load current changes capacitor values on the order of 100uF
are used in the output of many regulators. To further improve stability and transient response of these devices
larger values of output capacitor can be used.
PROTECTION DIODES
Unlike older regulators, the LM1085 family does not need any
protection diodies between the adjustment pin and the output and
from the output tu the input to prevent over-stressing the die.
Internal resistors are limiting the internal current paths on the
LM1085 adjustment pin, therfore even with capacitors on the
adjustment pin no protection diode is needed to ensure device
safety under short-circuit conditions.
LM1085
Diodes between the input and output are not usually needed.
Figure 10.
Microsecond surge currents of 50A to 100A can be handled by
the internal diode between the input and output pins of the device. In norminal operations it is difficult to get
those values of surge currents even with the use of large output capacitances. If high value output capacitors
are used, such as 1000uF to 5000uF and the input pin is instantaneously shorted to ground, damage can occur.
A diode from output to input is recommended, when a crowbar circuit at the input of the LM1085 is used.
Normal power supply cycling or even plugging and unplugging in the system will not generate current large
enough to do any damage.
The adjustment pin can be driven on a transient basis ±25V, with respect to the output without any device
degradation. As with any IC regulator, none the protection circuitry will be functional and the internal
transistors will break diwn if the maximum inout to output voltage differential is exceeded.
HTC
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HTC [ HTC KOREA TAEJIN TECHNOLOGY CO. ]
