ISL68221IRAZ datasheet(21/98 Pages) RENESAS

21 / 98 page

ISL68221

4. Operating the Device

FN9331 Rev.1.00

Page 21 of 97

Oct.1.20

4.9.4

Resistive Sensing

For more accurate current sensing, a dedicated current-sense resistor, RSENSE, in series with each output

inductor, can serve as the current-sense element. However, this technique reduces the overall converter

efficiency due to the additional power loss on the current-sense element, RSENSE.

A current-sensing resistor has a distributed parasitic inductance known as Equivalent Series Inductance (ESL),

which is typically less than 4nH. Consider the ESL as a separate lumped quantity, as shown in Figure 10. The

phase current, IL, flowing through the inductor, also passes through the ESL. Similar to DCR sensing described in

Inductor DCR Sensing, a simple R-C network across the current-sense resistor extracts the RSENSE voltage.

Match the ESL/RSENSE time constant to the R-C time constant.

Figure 11 shows the sensed waveforms with and without matching RC when using resistive sense. PCB layout for

resistive sense should follow the guidance described for DCR sense.

Figure 10. Sense Resistor in Series with Inductor

Figure 11. Voltage Across R with and without RC

ISL68221IRAZ Datasheet(PDF) 21 Page - Renesas Technology Corp