ADP3000

Rev. A | Page 10 of 16

APPLICATIONS INFORMATION

COMPONENT SELECTION

Inductor Selection

For most applications, the inductor used with the ADP3000

falls in the range of 4.7 µH to 33 µH. Table 4 shows

recommended inductors and their vendors.

When selecting an inductor for the ADP3000, it is very important

to make sure the inductor is able to handle a current higher than

the ADP3000’s current limit, without becoming saturated.

As a general rule, powdered iron cores saturate softly, whereas

Ferrite cores saturate abruptly. Rod and open drum core

geometry inductors saturate gradually. Inductors that saturate

gradually are easier to use. Even though rod and drum core

inductors are attractive in both price and physical size, they

must be used with care because they have high magnetic

radiation. When minimizing EMI is critical, toroid and closed

drum core geometry inductors should be used.

In addition, inductor dc resistance causes power loss. To

minimize power loss, it is best to use an inductor with a dc

resistance lower than 0.2 Ω.

Table 4. Recommended Inductors

Vendor

Series

Core Type

Phone Number

Coiltronics

OCTAPAC

Toroid

(561) 752-5000

Coiltronics

UNIPAC

Open

(561) 752-5000

Sumida

CR43, CR54

Open

(847) 545-6700

Sumida

CDRH6D28,

CDRH73,

CDRH64

Semi-Closed

Geometry

(847) 545-6700

Capacitor Selection

For most applications, the capacitor used with the ADP3000

falls in the range of 33 µF to 220 µF. Table 5 shows

recommended capacitors and their vendors.

For input and output capacitors, use low ESR type capacitors for

best efficiency and lowest ripple. Recommended capacitors

include the AVX TPS series, the Sprague 595D series, the

Panasonic HFQ series, and the Sanyo OS-CON series.

When selecting a capacitor, it is important to make sure the

maximum capacitor ripple current rms rating is higher than the

ADP3000’s rms switching current.

It is best to protect the input capacitor from high turn-on

current charging surges by derating the capacitor voltage by 2:1.

For very low input or output voltage ripple requirements, use

capacitors with very low ESR, such as the Sanyo OS-CON

series. Alternatively, two or more tantalum capacitors can be

used in parallel.

Table 5. Recommended Capacitors

Vendor

Series

Type

Phone Number

AVX

TPS

Surface Mount

(843) 448-9411

Sanyo

OS-CON

Through Hole

(619) 661-6835

Sprague

595D

Surface Mount

(603) 224-1961

Panasonic

HFQ

Through Hole

(800) 344-2112

Diode Selection

The ADP3000’s high switching speed demands the use of

Schottky diodes. Suitable choices include the 1N5817, the

1N5818, the 1N5819, the MBRS120LT3, and the MBR0520LT1.

Fast recovery diodes are not recommended because their high

forward drop lowers efficiency. General-purpose and small-

signal diodes should be avoided as well.

PROGRAMMING THE SWITCHING CURRENT LIMIT

current limit to be programmed with a single external resistor.

This feature offers major advantages that ultimately decrease

pin allows the ADP3000 to use low value, low saturation current

and physically small inductors. Additionally, it allows for a

physically small surface-mount tantalum capacitor with a

typical ESR of 0.1 Ω. With this capacitor, it achieves an output

ripple as low as 40 mV to 80 mV, as well as a low input ripple.

The current limit is usually set to approximately 3 to 5 times the

full load current for boost applications, and about 1.5 to 3 times

the full load current in buck applications.

Q1, the ADP3000’s internal power switch, is paralleled by sense

transistor Q2. The relative sizes of Q1 and Q2 are scaled so that

resistor and an internal 80 Ω resistor. The voltage on these two

resistors biases the base-emitter junction of the oscillator-disable

Q3 turns on and terminates the output pulse. If only the 80 Ω

and Figure 15 give values for lower current limit levels.

SW2

SW1

(EXTERNAL)

DRIVER

80

Ω

(INTERNAL)

200

Q2

ADP3000

Q1

400kHz

OSCILLATOR

Q3

R1

POWER

SWITCH

Figure 24. ADP3000 Current Limit Operation