LND1085/86

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.

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).

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

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.

• Linear Dimensions, Inc. • 445 East Ohio Street, Chicago IL 60611 USA • tel 312.321.1810 • fax 312.321.1830 • www.lineardimensions.com •

Figure 1. Output Voltage

Figure 2. Protection Diodes