Output Voltage

The LND5203 (adjustable version)

develops a 1.25V reference voltage

between the Sense pin and the Adjust

pin (Figure 4). 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 5mA. The

current out of the Adjust pin is small,

typically 50

µA and it adds to the

current from R1. For the best

regulation the top of the resistor

divider should be connected directly to

the Sense pin.

Protection Diodes

In normal operation LND5203 family does

not need any protection diodes between

the adjustment pin and 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. The adjust pin can be driver

on a transient basis ±7V with respect to

the output with out any device

degradation. A protection diode between

the Output pin and Vpower pin is not

usually needed. Microsecond surge

currents of 50A to 100A can be handled

by the internal diode between the Output

pin and Vpower 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

µF to 5000µF and the Vpower pin

are instantaneously shorted to ground,

damage can occur. A diode from output

to input is recommended (Figure 5).

If LND5203 is connected as a single

supply device with the control and power

input pins shorted together the internal

diode between the output and the power-

input pin will protect the control input pin.

Thermal Considerations

The LND5203 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 ambient, including junction-

to-case, case to-heat sink interface and

heat sink resistance itself.

Junction temperature of the control

section can run up to 125ºC. Junction

temperature of the Power section can run

up to 150ºC.

LND5203

LND5203

LND5203

Figure 4. Settling Output Voltage

Figure 5. Optional Clamp Diodes Protect Against

Input Crowbar Circuits

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