Data Sheet

ADP2386

Rev. A | Page 15 of 24

APPLICATIONS INFORMATION

INPUT CAPACITOR SELECTION

The input capacitor reduces the input voltage ripple caused by

the switch current on PVIN. Place the input capacitor as close

as possible to the PVIN pin. A ceramic capacitor in the 10 μF to

47 μF range is recommended. The loop that is composed of this

input capacitor, the high-side N-MOSFET, and the low-side N-

MOSFET must be kept as small as possible.

The voltage rating of the input capacitor must be greater than

the maximum input voltage. Ensure that the rms current rating

of the input capacitor is larger than the value calculated from

the following equation:

IN

)

1

(

D

D

−

×

OUTPUT VOLTAGE SETTING

The output voltage of the ADP2386 is set by an external resistive

divider. The resistor values are calculated using













+

BOT

TOP

R

R

1

To limit the output voltage accuracy degradation due to the FB

bias current (0.1 µA maximum) to less than 0.5% (maximum),

Table 6 lists the recommended resistor divider values for the

various output voltages.

Table 6. Resistor Divider Values for Various Output Voltages

1.0

1.2

1.5

1.8

2.5

3.3

5.0

10

10

15

20

47.5

10

22

15

10

10

10

15

2.21

3

VOLTAGE CONVERSION LIMITATIONS

The minimum output voltage for a given input voltage and

switching frequency is constrained by the minimum on time.

The minimum on time of the ADP2386 is typically 125 ns.

The minimum output voltage for a given input voltage and

switching frequency can be calculated using the following:

(1)

where:

The maximum output voltage for a given input voltage and

switching frequency is constrained by the minimum off time

and the maximum duty cycle. The minimum off time is typically

200 ns, and the maximum duty cycle of the ADP2386 is

typically 90%.

The maximum output voltage, limited by the minimum off time

at a given input voltage and switching frequency, can be calculated

using the following equation:

where:

The maximum output voltage, limited by the maximum duty

cycle at a given input voltage, can be calculated using the

following equation:

(3)

As shown in Equation 1 to Equation 3, reducing the switching

frequency alleviates the minimum on time and minimum off

time limitation.

INDUCTOR SELECTION

The inductor value is determined by the operating frequency,

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

a small inductor value leads to a faster transient response; however,

it degrades efficiency, due to a larger inductor ripple current.

Using a large inductor value leads to smaller ripple current and

better efficiency, but it results in a slower transient response.

to one-third of the maximum load current. The inductor value

is calculated using the following equation:

L =

SW

L

OUT

IN

f

I

D

V

V

×

∆

×

−

)

(

where:

The ADP2386 uses adaptive slope compensation in the current

loop to prevent subharmonic oscillations when the duty cycle

is larger than 50%. The internal slope compensation limits the

minimum inductor value.