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Data Sheet

ADPL74101

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If the external (R1||R2) × C1 time constant is chosen to be equal to the L/DCR time constant, the voltage drop across

the external capacitor is equal to the drop across the inductor DCR multiplied by R2/(R1+R2). R2 scales the voltage

across the sense terminals for applications where the DCR exceeds the target sense resistor value. To properly

dimension the external filter components, the inductor's DCR must be known. The DCR can be measured using an

inductance, capacitance, and resistance (LCR) meter. However, the DCR tolerance is not always the same and varies

with temperature. Refer to the manufacturer's data sheet for detailed information.

Using IL(MAX) and ΔIL (as described in the Inductor Value Calculation section), the target sense resistor value is given by

Equation 3, as follows:

RSENSE(EQUIV) =

VSENSE(MAX)

IL(MAX)+

∆IL

(3)

To ensure that the application delivers the full load current over the full operating temperature range, choose the

minimum value for VSENSE(MAX) in Table 1 (Electrical Characteristics table).

Next, determine the DCR of the inductor. When provided, use the maximum value noted by the manufacturer,

typically given at 20°C. Increase this value to account for the temperature coefficient of copper resistance, which is

approximately 0.4%/°C. A conservative value for the maximum inductor temperature (TL(MAX)) is 100°C. To scale the

maximum inductor DCR (DCRMAX) to the desired sense resistor (RD) value, use the divider ratio given by Equation 4, as

follows:

RD =

RSENSE(EQUIV)

DCRMAX at TL(MAX)

(4)

C1 is typically selected to be in the range of 0.1 μF to 0.47 μF. This range forces the equivalent resistance (R1||R2) to

around 2 kΩ, reducing the error that can result from the ≈1μA current of the SENSE+ pin.

R1||R2 is scaled to the room temperature inductance and maximum DCR given by Equation 5, as follows:

R1 ∥ R2 =

(DCR at 20°C) × C1

(5)

The sense resistor values are given by Equation 6 and Equation 7, as follows:

R1 =

R1∥R2

(6)

R1×RD

1− RD

(7)

The maximum power loss (PLOSS) in R1 is related to duty cycle and occurs in continuous mode at the maximum input

voltage (VIN(MAX)) given by Equation 8, as follows:

PLOSS in R1 =

(VIN(MAX)−VOUT)× VOUT

(8)

Ensure that R1 has a power rating higher than PLOSS in R1. If high efficiency is necessary at light loads, consider this

power loss when deciding whether to use DCR sensing or sense resistors. Light-load power loss can be modestly

higher with a DCR network than with a sense resistor, due to the extra switching losses incurred through R1. However,

DCR sensing eliminates the need for a sense resistor, reduces conduction losses, and provides higher efficiency at

heavy loads. Peak efficiency is about the same with either method.

ADPL74101 Datasheet(PDF) 26 Page - Analog Devices

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