Application information

RHFL4913XX15 - RHFLXX25 - RHFLXX33 - RHFLXX50

10/19

6

Application information

load” regulation.

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 drop out operation: minimum 1 µF

input and output tantalum capacitors are therefore mandatory. Capacitor ESR range is from

0.5

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 RHFL4913 fixed voltage manufactured with very high speed bipolar technology 6 GHz

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.