AN2984

Doc ID 15690 Rev 1

3/8

to the device terminals. As some tantalum capacitors may permanently fail when subjected

to high charge-up surge currents, it is recommended to decouple them with 470 nF

polyester capacitors.

As the RHFL4913A adjustable voltage regulator is manufactured with very high speed

care, with very low inductance and low mutually coupling lines. Otherwise, high frequency

parasitic signals may be picked up by the device resulting in system self-oscillation. The

benefit is an SVR performance extended to far higher frequencies.

In order to replace a standard 3-terminal industry device, fixed voltage versions are

available.

A separate Kelvin voltage sensing line provides the ADJ pin with exact load “high potential”

information. But variable remote load current consumption induces variable Iq current (Iq is

through the parasitic series line RW2 resistor. To compensate for this parasitic voltage, an

RW1 resistor can be introduced to provide the necessary compensating voltage signal to

the ADJ pin, as shown in Figure 3.

In the case of an FPGA power supply, as these devices are very sensitive to VDD transients

beyond a small percentage of their nominal supply voltage (usually 1.5 V), special attention

must be taken to mitigate possible heavy-ion disturbances. The worst case heavy-ion effect

can be summarized as the following: the RHFL4913A internal control loop being cut

(opened) or short-circuited for a sub-microsecond duration. During such an event, the

RHFL4913A die power element can either provide excessive current or current supply

voltage regulator smoothly recovers to nominal operation. To mitigate these “transients”, it is

recommended to firstly implement the PCB layout using the following notes:

●

Minimizing series/parallel parasitic inductances of the PC path;

●

capacitor in parallel with the former (to reduce dynamic ESR);

With this implementation, the ELDO simulated worst transient case shows no more than a

90 mV deviation from the nominal line voltage value.

Figure 3.

Application schematic for remote load operation