lnd1085 Linear Dimensions Semiconductor, lnd1085 Datasheet - Page 4

• Manufacturer Part Number: lnd1085
• Description: 1.5 A / 3 A Low Dropout Voltage Regulators
• Manufacturer: Linear Dimensions Semiconductor

• Linear Dimensions, Inc. • 445 East Ohio Street, Chicago IL 60611 USA • tel [phone] • fax [phone] •
APPLICATIONS INFORMATION
The LND1086 family of three-terminal
adjustable regulators is easy to use and has all
the protection features that are expected in
high performance voltage regulators.
Stability
The circuit design used in the LND1086 series
requires the use of an output capacitor as part
of the device frequency compensation. The
addition of 150 µF aluminum electrolytic or a
22 µF solid tantalum on the output will ensure
stability for all operating conditions.
Output Voltage
The LND1086 develops a 1.25V reference
voltage between the Output pin and the Adjust
pin (Figure 1). Placing a resistor between
these two terminals causes a constant current
to flow through R1 and down though R2 to set
the output voltage. In general R1 is chosen so
that this current is the specified minimum load
current of 10mA. The current out of the Adjust
pin is small as compared to the current from
R1 and can be ignored. For fixed voltage
devices R1 and R2 are included in the device.
Protection Diodes
In normal operation LND1086 family does not
need any protection diodes between the
adjustment pin and the output and from the
output to the input to prevent die
overstresses. Internal resistors are limiting
the internal current paths on the ADJ pin.
Therefore even with bypass capacitors on
the adjust pin no protection diode is needed
to ensure device safety under short-circuit
conditions
Figure 1. Output Voltage
Microsecond surge currents of 10A to 20A
can be handled by the internal diode
between the Output pin and the Input pin of
the device. In normal operations it is difficult
to get those values of surge currents even
with the use of large output capacitance.
Only with high value output capacitors, such
as 1000 to 5000µF and with the Input pin
instantaneously shorted to ground, can
damage occur. A diode from output to input
is recommended (Figure 2).
Thermal Considerations
The LND1086 series have internal power and
thermal-limiting circuitry designed to protect
the device under overload conditions.
However, maximum junction temperature
ratings should not be exceeded under
continuous normal load conditions. Careful
consideration must be given to all sources of
thermal resistance from junction to ambient,
including junction-to-case, case to-heat sink
interface and heat sink resistance itself.
Figure 2. Protection Diodes
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LND1085/86
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