ADP5080 datasheet(35/64 Pages) AD

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Data Sheet

ADP5080

Table 13. Suggested Inductors

Channel

VOUT (V)

Frequency (kHz)

Inductance (µH)

Part Number

<1.0

750 or 1000

Toko FDSD0420-H-1R0

1500 or 2000

0.47

Toko FDSD0420-H-R47

1.0 to 1.2

750 or 1000

1.5

Toko FDSD0420-H-1R5

1500 or 2000

0.68

Toko FDSD0420-H-R68

<1.8

750 or 1000

4.7

Toko FDSD0420-H-4R7

1500 or 2000

2.2

Toko FDSD0420-H-2R2

1.8 to 3.3

750 or 1000

6.8

Taiyo Yuden NRS4018T6R8M

1500 or 2000

3.3

Toko FDSD0420-H-3R3

<1.5

750 or 1000

3.3

Toko FDSD0420-H-3R3

1500 or 2000

1.5

Toko FDSD0420-H-1R5

1.5 to 1.8

750 or 1000

3.3

Toko FDSD0420-H-3R3

1500 or 2000

1.5

Toko FDSD0420-H-1R5

<2.5

750 or 1000

6.8

Taiyo Yuden NRS4018T6R8M

1500 or 2000

3.3

Toko FDSD0420-H-3R3

2.5 to 3.55

750 or 1000

Taiyo Yuden NRS4018T100M

1500 or 2000

4.7

Toko FDSD0420-H-4R7

750 or 1000

3.3

Toko FDSD0420-H-3R3

1500 or 2000

2.2

Toko FDSD0420-H-2R2

4 to 5

750 or 1000

3.3

Toko FDSD0420-H-3R3

1500 or 2000

1.5

Toko FDSD0420-H-1R5

<4.5

750 or 1000

4.7

Toko FDSD0420-H-4R7

1500 or 2000

2.2

Toko FDSD0420-H-2R2

4.5 to 5.5

750 or 1000

4.7

Toko FDSD0420-H-4R7

1500 or 2000

3.3

Toko FDSD0420-H-3R3

Selecting the Input Capacitor

Step-down switching regulators draw current from the input

supply in pulses that have very fast rise and fall times. Low ESR

ceramic input capacitors are required to reduce the input voltage

ripple and provide bypass for high frequency switching noise. If

not well bypassed, the input noise can cause poor device perfor-

mance, instability, and increased conducted and radiated emissions

(EMI).

Each switching channel should have approximately 10 µF of

input bypass capacitance. Place the input capacitors as close

as possible to the PVINx and PGNDx pins. Place an additional

ceramic input capacitor at VBATT. It is usually beneficial to use

multiple capacitors in parallel instead of a single high value

capacitor.

Note that ceramic capacitors have very strong dc bias character-

istics and lose as much as 80% of their capacitance value at the

rated voltage. Also, note that the rise in case temperature due to

rms current in the input capacitor can be quite high on the input

of a buck regulator. For these reasons, capacitors of X5R and X7R

type or better are recommended. A good estimate for the rms

current in the input capacitor of a single channel is

OUT

LOAD

RMS

)

(

−

Selecting the Output Capacitor

The output capacitor is important for regulator operation

because it affects the loop stability, output voltage ripple, and

load transient response.

The ADP5080 is designed to operate with low ESR ceramic

output capacitors. Higher output capacitor values reduce the

output voltage ripple and improve load transient step response.

When choosing an output capacitor value, it is also important to

account for the loss of capacitance due to output voltage dc bias.

Table 14 lists the minimum recommended capacitor values for

each channel. Note that the capacitor values shown in Table 14

are nominal values, not derated values. The capacitors listed

work for the full range of operating frequency and load.

Lower values can be used at higher frequency or lighter load

currents. However, exercise caution when using values smaller

than the minimum recommended values; too small an output

capacitor can result in unstable operation. Output capacitance

can typically be increased with no practical limit without causing

stability problems. Greater capacitance improves ripple and

transient performance.

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