ISL68227IRAZ datasheet(22/100 Pages) RENESAS

22 / 100 page

ISL68227

4. Operating the Device

FN9333 Rev.1.00

Page 22 of 99

Oct.1.20

4.10.3 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 11 on

page 22. 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 12 shows the sensed waveforms with and without matching RC when using resistive sense. PCB layout

for resistive sense should follow the guidance described in “Inductor DCR Sensing” on page 21.

Figure 11. Sense Resistor in Series with Inductor

Figure 12. Voltage Across R with and without RC

ISL68227IRAZ Datasheet(PDF) 22 Page - Renesas Technology Corp