Application information

RHFL4913 ADJUSTABLE VERSION

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5

Application information

connected between ADJ and Ground. Resistor values can be derived from the following formula:

The minimum Output voltage is therefore 1.22V and minimum Input voltage is 3V.

element saturation voltage. The Adjust pin to Ground resistor must not be bigger than 10k

reliability cannot be granted. The INHIBIT function switches off the output current in an electronic way,

that is very quickly. According to Lenz’s Law, external circuitry reacts with LdI/dt terms which can be of

high amplitude in case somewhere an inductance exists. Large transient voltage would develop on both

Device terminals. It is advisable to protect the Device with Schottky diodes preventing negative voltage

excursions. In the worst case, a 14V Zener diode shall protect the Device Input. The Device has been

designed for high stability and low drop out operation: Minimum 1µF input and output tantalum capacitors

are therefore mandatory. Capacitor ESR range is from 0.5

useful when ESR increases at low temperature. When large transient currents are expected, larger value

capacitors are necessary.

In case of high current operation with expected short-circuit events, caution must be considered relatively

to capacitors. They must be connected as close as possible to device terminals. As some tantalum

capacitors may permanently fail when submitted to high charge-up surge currents, it is recommended to

decouple them with 470nF polyester capacitors.

PCB layout must be performed with exceptional care, very low inductance, low mutually coupling lines,

otherwise high frequency parasitic signals may be picked-up by the Device resulting into system

self-

oscillation. The benefit is an SVR performance extended to far higher frequencies.

5.1

Notes about 16pin hermetic package

The bottom section of 16pin packages is metallized in order to allow User to directly solder the

RHFL4913A on the equipment heat sink for enhanced heat removal.

5.2

Remote sensing operation

See

Figure 2. A separate Kelvin Voltage sensing line provides ADJ pin with exact Load "high potential"

information. But variable remote Load current consumption induces variable Iq current (Iq is roughly the

line resistor symbolized as RW2. To compensate this parasitic voltage, the Resistor RW1 introduced on

purpose provides the necessary compensating voltage signal to ADJust pin.