ADP3050ARZ-3.3-RL View Datasheet(PDF) - Analog Devices

Part Name

Description

Manufacturer

ADP3050ARZ-3.3-RL

200 kHz, 1 A High Voltage Step-Down Switching Regulator

Analog Devices 

Data Sheet

ADP3050

low ESR (a 22 μF ceramic can have an ESR one-fifth that of a

22 μF solid tantalum), but may require more board area for the

same value of output capacitance. A few manufacturers have

recently improved upon their low voltage ceramic capacitors,

providing a smaller package with a lower ESR (NEC Tokin,

Murata, Taiyo Yuden, and AVX). Several ceramics can be used

in parallel to give an extremely low ESR and a good value of

capacitance. If the design is cost sensitive and not severely space

limited, several aluminum electrolytic capacitors can be used in

parallel (their size and ESR are larger than ceramic and solid

tantalum). OS-CON capacitors can also be used, but they are

typically larger and more expensive than ceramic or solid

tantalum capacitors.

1 A) and fast switching speed of a Schottky rectifier provide the

best performance and efficiency. The 1N5818 is rated at 30 V

reverse voltage and 1 A average forward current. For lower

input voltages, use a lower voltage Schottky to reduce the diode

forward voltage drop and increase overall system efficiency; for

example, a 12 V to 5 V system does not need a 30 V diode. For

automotive applications, a 60 V Schottky may be necessary. The

average forward current for the catch diode is calculated by

I DIODE(AVG)

=

I OUT

× VIN −VOUT

VIN

(5)

For the earlier continuous mode example (12 V to 5 V at

800 mA), the average diode current is

Choosing an Output Capacitor

12 − 5

Use the following steps to choose an appropriate capacitor.

I DIODE(AVG) = 0.8× 12 = 0.47 A

(6)

1. Decide the maximum output ripple voltage for the design,

and this determines your maximum ESR (remember that

VRIPPLE ≈ ESR × IRIPPLE). Typical output ripple voltages range

between 0.5% and 2% of the output voltage. To lower the

output voltage ripple, there are only two choices: either

increase the inductor value, or use an output capacitor with

a lower ESR.

2. Decide what type of capacitor to use (tantalum, ceramic, or

others). Many more values, sizes, and voltage ratings are

available, so contact each manufacturer for a complete

product list. If a certain type of capacitor must be used and

space permits, use several devices in parallel to reduce the

total ESR.

3. Check the capacitor voltage rating and ripple current rating

to ensure it works for the application in question. These

ratings are derated for higher temperatures, so always check

the manufacturer’s data sheet.

4. Make sure the final choice for the output capacitor has

been optimized for cost, size, availability, and performance

yet still meets the required capacitance. The recommended

capacitance is in the 47 μF to 220 μF range.

CATCH DIODE SELECTION

For this system, a 1N5817 is a good choice (rated at 20 V and 1 A).

Do not use catch diodes rated less than 1 A. Even though the

average current can be less than 1 A under normal operating

conditions, as the diode current is much higher under fault

conditions. The worst-case fault condition for the diode occurs

when the regulator becomes slightly overloaded (sometimes

called a soft short). This is usually only a problem when the

input voltage to output voltage ratio is greater than 2.5. Under

this condition, the load current needed is slightly more than the

regulator can provide. The output voltage droops slightly, and

the switch stays on every cycle until the internal current limit is

reached. Under this condition, the load current can reach

around 1.2 A. For example, when using a system with an input

voltage of 24 V and an output voltage of 5 V, if a gradual overload

causes the output voltage to droop to 4 V, the average diode

current is

24 − 4

I DIODE(AVG) =1.2 × 24 =1.0 A

(7)

If the system must survive such gradual overloads for a prolonged

period of time, ensure the diode chosen can survive these

conditions. A larger 2 A or 3 A diode can be used if necessary.

The recommended catch diode is a Type 1N5818 Schottky or

equivalent. The low forward voltage drop (450 mV typical at

Table 4. Manufacturers

Inductor Manufacturers

Sumida

Coilcraft

Cooper Bussmann Coiltronics

NEC Tokin

Würth Elektronik

Toko

Capacitor Manufacturers

AVX

Kemet

Murata

Nemco

Vishay Sprague

NEC Tokin

Taiyo Yuden

Schottky Diode Manufacturers

Motorola

Diodes, Inc.

International Rectifier

Nihon Inter Electronics

Rev. C | Page 13 of 20

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