Data Sheet

ADP1614

Rev. 0 | Page 13 of 16

CHOOSING THE INPUT AND OUTPUT CAPACITORS

The ADP1614 requires input and output bypass capacitors to

supply transient currents while maintaining constant input

and output voltages. Use low equivalent series resistance (ESR)

capacitors of 10 µF or greater to prevent noise at the ADP1614

input. Place the capacitor between VIN and GND, as close as

possible to the ADP1614. Ceramic capacitors are preferable

because of their low ESR characteristics. Alternatively, use a

high value, medium ESR capacitor in parallel with a 0.1 µF low

ESR capacitor, placed as close as possible to the ADP1614.

The output capacitor maintains the output voltage and supplies

current to the load while the ADP1614 switch is on. The value

and characteristics of the output capacitor greatly affect the

output voltage ripple and stability of the regulator. A low ESR

ceramic dielectric capacitor is preferable. The output voltage

OUT

ON

OUT

OUT

C

OUT

C

t

I

C

Q

V

×

=

=

∆

(8)

where:

The on time of the switch is determined as follows:

SW

ON

f

D

t

=

(9)

switch duty cycle (D) as follows:

OUT

IN

OUT

V

V

V

D

−

=

(10)

Choose the output capacitor based on the following equation:

OUT

OUT

SW

IN

OUT

OUT

OUT

V

V

f

V

V

I

C

∆

×

×

−

×

≥

)

(

(11)

Multilayer ceramic capacitors are recommended for this

application.

DIODE SELECTION

The output rectifier conducts the inductor current to the output

capacitor and load while the switch is off. For high efficiency,

minimize the forward voltage drop of the diode. For this reason,

using Schottky rectifiers is recommended. However, for high

voltage, high temperature applications, where the Schottky

rectifier reverse leakage current becomes significant and can

degrade efficiency, use an ultrafast junction diode.

Many diode manufacturers derate the current capability of the

diode as a function of the duty cycle. Verify that the output

diode is rated to handle the average output load current with

the minimum duty cycle. The minimum duty cycle in CCM of

the ADP1614 is

OUT

MAX

IN

OUT

MIN

V

V

V

D

)

(

−

=

(12)

The following are suggested Schottky diode manufacturers:

•

ON Semiconductor

•

Diodes, Inc.

•

Toshiba

•

ROHM Semiconductor

LOOP COMPENSATION

The ADP1614 uses external components to compensate the

regulator loop, allowing optimization of the loop dynamics for a

given application.

The step-up converter produces an undesirable right-half plane

zero in the regulation feedback loop. This requires compensating

the regulator such that the crossover frequency occurs well below

the frequency of the right-half plane zero. The right-half plane

zero is determined by the following equation:

L

R

V

V

RHP

F

LOAD

OUT

IN

Z

×

π

×













=

2

)

(

2

(13)

where:

divided by the load current.

To stabilize the regulator, ensure that the regulator crossover

frequency is less than or equal to one-fifth of the right-half

plane zero.

The regulator loop gain is

OUT

CS

COMP

OUT

MEA

OUT

IN

OUT

FB

VL

Z

G

Z

R

G

V

V

V

V

A

×

×

×

×

×

=

(14)

where:

to GND.

current divided by the voltage at COMP), which is internally

set by the ADP1614.

capacitor.