ADP1614

Data Sheet

Rev. 0 | Page 14 of 16

To determine the crossover frequency, it is important to note that

dominated by the impedance of an output capacitor. Therefore,

when solving for the crossover frequency, the equation (by defi-

nition of the crossover frequency) is simplified to

1

2

1

=

×

×

π

×

×

×

×

×

=

OUT

C

CS

COMP

MEA

OUT

IN

OUT

FB

VL

C

f

G

R

G

V

V

V

V

A

(15)

where:

CS

MEA

IN

FB

OUT

OUT

C

COMP

G

G

V

V

V

C

f

R

×

×

×

×

×

×

π

=

2

)

(

2

(16)

where:

Therefore,

IN

OUT

OUT

C

COMP

V

V

C

f

R

2

)

(

4806

×

×

×

=

(17)

After the compensation resistor is known, set the zero formed

by the compensation capacitor and resistor to one-fourth of the

crossover frequency, or

COMP

C

COMP

R

f

C

×

×

π

=

2

(18)

C2

1

COMP

ERROR

AMPLIFIER

2

FB

Figure 27. Compensation Components

Capacitor C2 is chosen to cancel the zero introduced by the ESR

of the output capacitor.

Solve for C2 as follows:

COMP

OUT

R

C

ESR

C2

×

=

(19)

might need to be adjusted by observing the load transient response

of the ADP1614. For most applications, the compensation resistor

should be within the range of 1 kΩ to 100 kΩ, and the compen-

sation capacitor should be within the range of 100 pF to 10 nF.

SOFT START CAPACITOR

Upon startup (EN ≥ 1.6 V) or fault recovery, the voltage at SS

capacitor charges, it limits the peak current allowed by the part

to prevent excessive overshoot at startup. Use the following

equation to determine the necessary value of the soft start

the part is at the current limit with maximum load:

SS

SS

SS

V

t

I

C

∆

=

(20)

where:

Δt is the start-up time at the current limit.

If the applied load does not place the part at the current limit,

results in negligible input current overshoot at startup and,

therefore, is suitable for most applications. If an unusually large

output capacitor is used, a longer soft start period is required to

prevent input inrush current.

However, if fast startup is required, the soft start capacitor can

be reduced or removed, which allows the ADP1614 to start

quickly but with greater peak switch current.