ADP2105ACPZ-3.3-R7 datasheet(16/32 Pages) AD

16 / 32 page

ADP2105/ADP2106/ADP2107

Rev. 0 | Page 16 of 32

Once RBOT is determined, calculate the value of the top resistor,

RTOP, by

⎥

⎦

⎤

⎢

⎣

⎡

−

OUT

BOT

TOP

The ADP2105/ADP2106/ADP2107-xx (where xx represents

the fixed output voltage) include the resistive voltage divider

internally, reducing the external circuitry required. Connect the

OUT_SENSE to the output voltage as close as possible to the

load for improved load regulation.

INDUCTOR SELECTION

The high switching frequency of ADP2105/ADP2106/ADP2107

allows for minimal output voltage ripple even with small inductors.

The sizing of the inductor is a trade-off between efficiency and

transient response. A small inductor leads to larger inductor

current ripple that provides excellent transient response but

degrades efficiency. Due to the high switching frequency of

ADP2105/ADP2106/ADP2107, shielded ferrite core inductors

are recommended for their low core losses and low EMI.

As a guideline, the inductor peak-to-peak current ripple, ΔIL,

is typically set to 1/3 of the maximum load current for optimal

transient response and efficiency.

)

(

)

(MAX

LOAD

OUT

≈

−

)

(

)

(MAX

LOAD

OUT

IDEAL

−

⇒

where fSW is the switching frequency (1.2 MHz).

The ADP2105/ADP2106/ADP2107 use slope compensation in

the current control loop to prevent subharmonic oscillations

when operating beyond 50% duty cycle. The fixed slope compen-

sation limits the minimum inductor value as a function of

output voltage.

For the ADP2105:

L > (1.12 μH/V) × VOUT

For the ADP2106:

L > (0.83 μH/V) × VOUT

For the ADP2107:

L > (0.66 μH/V) × VOUT

Also, 4.7 μH or larger inductors are not recommended because

they may cause instability in discontinuous conduction mode

under light load conditions.

Finally, it is important that the inductor be capable of handling

the maximum peak inductor current, IPK, determined by the

following equation:

⎟

⎠

⎞

⎜

⎝

⎛ Δ

)

(

MAX

LOAD

Ensure that the maximum rms current of the inductor is greater

than the maximum load current, and the saturation current of

the inductor is greater than the peak current limit of the converter

used in the application.

Table 5. Minimum Inductor Value for Common Output

Voltage Options for the ADP2105 (1 A)

VIN

VOUT

2.7 V

3.6 V

4.2 V

5.5 V

1.2 V

1.67 μH

2.00 μH

2.14 μH

2.35 μH

1.5 V

1.68 μH

2.19 μH

2.41 μH

2.73 μH

1.8 V

2.02 μH

2.25 μH

2.57 μH

3.03 μH

2.5 V

2.80 μH

3.41 μH

3.3 V

3.70 μH

Table 6. Minimum Inductor Value for Common Output

Voltage Options for the ADP2106 (1.5 A)

VIN

VOUT

2.7 V

3.6 V

4.2 V

5.5 V

1.2 V

1.11 μH

2.33 μH

2.43 μH

1.56 μH

1.5 V

1.25 μH

1.46 μH

1.61 μH

1.82 μH

1.8 V

1.49 μH

1.50 μH

1.71 μH

2.02 μH

2.5 V

2.08 μH

2.27 μH

3.3 V

2.74 μH

Table 7. Minimum Inductor Value for Common Output

Voltage Options for the ADP2107 (2 A)

VIN

VOUT

2.7 V

3.6 V

4.2 V

5.5 V

1.2 V

0.83 μH

1.00 μH

1.07 μH

1.17 μH

1.5 V

0.99 μH

1.09 μH

1.21 μH

1.36 μH

1.8 V

1.19 μH

1.29 μH

1.51 μH

2.5 V

1.65 μH

1.70 μH

3.3 V

2.18 μH

Table 8. Inductor Recommendations for the ADP2105/

ADP2106/ADP2107

Vendor

Small-Sized Inductors

( < 5 mm × 5 mm)

Large-Sized Inductors

( > 5 mm × 5 mm)

Sumida

CDRH2D14, 3D16,

3D28

CDRH4D18, 4D22,

4D28, 5D18, 6D12

Toko

1069AS-DB3018,

1098AS-DE2812,

1070AS-DB3020

D52LC, D518LC,

D62LCB

Coilcraft

LPS3015, LPS4012,

DO3314

DO1605T

Cooper

Bussmann

SD3110, SD3112,

SD3114, SD3118,

SD3812, SD3814

SD10, SD12, SD14, SD52

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