ADP5014ACPZ-R7 datasheet(23/34 Pages) AD

23 / 34 page

Data Sheet

ADP5014

Rev. A | Page 23 of 34

The maximum output voltage for a given input voltage and

switching frequency is limited by the minimum off time or the

maximum duty cycle. The minimum off time for each channel

is 50 ns (typical).

The maximum output voltage for a given input voltage and

switching frequency is calculated using the following equation:

VOUT_MAX = VIN × (1 − tMIN_OFF × fSW) − (RDSON1 − RDSON2) ×

IOUT_MAX × (1 − tMIN_OFF × fSW) − (RDSON2 + RL) × IOUT_MAX (2)

where:

VOUT_MAX is the maximum output voltage.

tMIN_OFF is the minimum off time.

fSW is the switching frequency.

RDSON1 is the high-side MOSFET on resistance.

RDSON2 is the low-side MOSFET on resistance.

IOUT_MAX is the maximum output current.

RL is the resistance of the output inductor.

As shown in Equation 1 and Equation 2, reducing the switching

frequency eases the minimum on time and off time limitations.

CURRENT-LIMIT SETTING

The ADP5014 has two selectable current-limit thresholds for

each channel. Ensure that the selected current-limit value is

larger than the peak current of the inductor, IPEAK. See Table 6

for the current-limit configuration for each channel.

SOFT START SETTING

The buck regulators in the ADP5014 include soft start circuitry

that ramps the output voltage in a controlled manner during

startup, thereby limiting the inrush current. To set the soft start

time to a value of 2 ms or 16 ms, connect a resistor from the

CFG2 pin to the ground (see the Soft Start section).

INDUCTOR SELECTION

The inductor value is determined by the operating frequency,

input voltage, output voltage, and inductor ripple current. Using

a small inductor yields faster transient response but degrades

efficiency due to the larger inductor ripple current. Using a large

inductor value yields a smaller ripple current and better efficiency,

but results in slower transient response. Therefore, a trade-off

must be made between the transient response and efficiency. As

a guideline, the inductor ripple current, ΔIL, is typically set to a

value from 30% to 40% of the maximum load current. The

inductor value is calculated using the following equation:

L = [(VIN − VOUT) × D]/(ΔIL × fSW)

where:

VIN is the input voltage.

VOUT is the output voltage.

D is the duty cycle (D = VOUT/VIN).

ΔIL is the inductor ripple current.

fSW is the switching frequency.

The ADP5014 has internal slope compensation in the current

loop to prevent subharmonic oscillations when the duty cycle is

greater than 50%.The inductor peak current is calculated using

the following equation:

IPEAK = IOUT + (ΔIL/2)

The saturation current of the inductor must be larger than the

peak inductor current. For ferrite core inductors with a fast

saturation characteristic, the saturation current rating of the

inductor are higher than the current-limit threshold of the buck

regulator to prevent the inductor from becoming saturated.

The rms current of the inductor is calculated using the

following equation:

OUT

RMS

∆

Shielded ferrite core materials are recommended for low core

loss and low electromagnetic interference (EMI). Table 11 lists

the recommended inductors.

Table 11. Recommended Inductors

Vendor

Part No.

Value (µH)

ISAT (A)

IRMS (A)

DCR (mΩ)

Size (mm)

Coilcraft

XAL4020-601

0.6

10.4

11.7

9.5

4 × 4

XAL4020-102

1.0

8.7

9.6

13.3

4 × 4

XAL4020-152

1.5

7.1

7.5

21.5

4 × 4

XAL4020-222

2.2

5.6

5.5

35.2

4 × 4

TOKO

DFE252012P-R68M

0.68

5.3

4.1

2.5 × 2.0

DFE252012P-1R0P

1.0

4.8

3.8

2.5 × 2.0

DFE252012P-1R5P

1.5

3.9

3.0

2.5 × 2.0

DFE252012P-2R2P

2.2

3.4

2.6

2.5 × 2.0

Wurth

744383560068

0.68

9.4

8.2

7.5

4.1 × 4.1

74438356010

9.0

7.2

4.1 × 4.1

74438356015

1.5

7.8

5.8

4.1 × 4.1

74438356022

2.2

6.2

4.7

4.1 × 4.1

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