ADPL74101 datasheet(25/49 Pages) AD

25 / 49 page

Data Sheet

ADPL74101

analog.com

Rev. 0

25 of 49

The parasitic inductance (ESL) of the sense resistor introduces significant error in the current sense signal for lower

inductor values (<3μH) or higher current (>5A) applications. This error is proportional to the input voltage and can

degrade line regulation or cause loop instability. Placing an RC filter (RF) into the sense pins, as shown in Figure 30,

can be used to compensate for this error. For optimal cancellation of the ESL, set the RC filter time constant to RF ×

CF = ESL/RSENSE (CF is the filter capacitor). In general, select CF to be in the range of 1 nF to 10 nF and calculate the

corresponding RF. Surface-mount sense resistors in low ESL, wide footprint geometries are recommended to

minimize this error. If not specified in the data sheet of the manufacturer, the ESL can be approximated as 0.4nH for

a resistor with a 1206 footprint, and 0.2nH for a resistor with a 1225 footprint.

Figure 30. Using a Resistor to Sense Current

Inductor DCR Current Sensing

For applications requiring the highest possible efficiency at high load currents, the ADPL74101 is capable of sensing

the voltage drop across the inductor DCR, as shown in Figure 31. The DCR of the inductor represents the small amount

of DC winding resistance of the copper, which can be less than 1mΩ for low-value, high-current inductors. In a high-

current application requiring such an inductor, power loss through a sense resistor costs several points of efficiency

compared to inductor DCR sensing.

Figure 31. Using the Inductor DCR to Sense Current (RSENSE(EQUIV) is the Equivalent Sensed Resistance)

RSENSE

ESL

ADPL74101

BOOST

SENSE+

SENSE–

VOUT

COUT

CIN

VIN

PLACE RF AND CF NEAR SENSE+ AND SENSE–

TOP

BOT

ADPL74101

VIN

CIN

VOUT

COUT

C1*

*PLACE C1 NEAR SENSE + AND SENSE–

**PLACE R1 NEAR SW NODE

RSENSE(EQUIV) = DCR(R2/(R1 + R2))

DCR

R1**

(R1||R2) × C1 = L/DCR

BOOST

GND

SENSE–

SENSE+

BOT

TOP

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