6

Application information

The RHFL4913 fixed voltage is functional as soon as VI-VO voltage difference is slightly above the power element

saturation voltage. A minimum 0.5 mA IO ensures perfect “no-load” regulation.

All available VI pins must always be externally interconnected, same thing for all available VO pins, otherwise

device stability and reliability cannot be granted. All NC pins can be connected to ground. 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 some series-inductance exists. The effect

would be a large transient voltage developed on both device terminals. It is necessary to protect the device with

Schottky diodes preventing negative voltage excursions. In the worst case, a 14 V Zener diode shall protect the

device input.

The device has been designed for high stability and low dropout operation: minimum 1 μF input and output

tantalum capacitors are therefore mandatory. Capacitor ESR range is from 0.01 Ω to over 20 Ω. Such range turns

out to be 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 470

nF polyester capacitors.

Being the RHFL4913 fixed voltage manufactured with very high speed bipolar technology 6 GHz fT transistors),

the PCB lay-out must be performed with extreme care, very low inductance, low mutually coupling lines,

otherwise high frequency parasitic signals may be picked-up by the device resulting into self-oscillation. User’s

benefit is a SVR performance extended to far

higher frequencies.

6.1

Remote sensing operation

In case the load is located far from the regulator, it is recommended to comply with the scheme below. To obtain

the best regulation, it is in addition essential to care about:

•

The wire connecting R2 to the load end must not be crossed by the load current (Kelvin sense)

The noise captured by the wires between the load and the chip could bring a noisy output voltage. In case this

happens, it is recommended that shielded cables are used for these connections. The external wrap must be

used for connecting the ground of the chip with the load ground. It is also recommended to place 1 μF tantalum

capacitors between output and ground close to the device and another next to the load.

RHFL4913XX25, RHFL4913XX33, RHFL4913XX50

Application information

DS3260 - Rev 15

page 8/20