ISL68227IRAZ datasheet(21/100 Pages) RENESAS

21 / 100 page

ISL68227

4. Operating the Device

FN9333 Rev.1.00

Page 21 of 99

Oct.1.20

4.10 Output Current Sensing

The ISL68227 supports DCR, resistor, and smart power stage current sensing. Use the differential input CS and

CSRTN pins to connect to the various sense elements.

4.10.1 SPS Current Sensing

In applications using Smart Power Stage (SPS), the SPS IMON output is connected to the corresponding

ISL68227 CSn input. The CSRTNn pins are connected to the SPS current sense reference voltage. For

connection details, see the typical application diagram shown in Figure 1 on page 6.

4.10.2 Inductor DCR Sensing

Inductor windings have a resistive component (DCR) that drops a voltage proportional to the inductor current.

Figure 10 shows that the DCR is treated as a lumped element with one terminal inaccessible for measurement.

Fortunately, a simple R-C network as shown in Figure 10 can reproduce the hidden DCR voltage. By matching the

R-C time constant to the L divided by DCR time constant, it is possible to precisely recreate the DCR voltage

across the capacitor, so that VDCR(t) = VC(t), preserving even the switching frequency characteristic of the DCR

voltage.

Modern inductors often have such low DCR values that the resulting signal is <10mV. To avoid noise problems,

care must be taken in the PCB layout to properly place the R-C components and route the differential lines

between controller and inductor. Figure 10 shows one PCB design method that places the R component near the

inductor VPHASE and the C component very close to the IC pins. The design method maintains isolation of the

noisy VPHASE node and maximizes filtering near the IC. Route the lines as a pair on a single layer directly to the

controller. Avoid routing the pair near any switching signals such as Phase and PWM. This is the method used by

Renesas on evaluation board designs. Note: The R component should be 0603 or greater size to limit the effects

of voltage coefficient of resistance in the resistor.

Because the DCR is actually the resistance of a metal winding, the DCR value increases with rising temperature.

The increase must be compensated or the sensed (and reported) current increases with temperature. To

compensate the temperature effect, the ISL68227 provides temperature sensing options and an internal

methodology to apply the correction.

Figure 10. DCR Sensing Configuration

ISL68227IRAZ Datasheet(PDF) 21 Page - Renesas Technology Corp