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LT3582EUD

I2C Programmable Boost and Single Inductor Inverting DC/DC Converters with OTP

Linear Technology 

LT3582/LT3582-5/LT3582-12

APPLICATIONS INFORMATION

Where…

VOUT = Regulation voltage

VIN(MIN) = Minimum input voltage.

IPK = Peak inductor current. See prior section

Peak Current Rating. Use minimum ILimit

rating for these calculations.

η

= Power conversion efficiency (about 88%

for Boost or 78% for Inverting)

TOFF_MIN = Minimum switch off time. Typically

100ns for Boost and 125ns for Inverting.

IOUT = Output load current

For example, if VOUTP = 10V, VOUTN = –10V, VIN = 5V, and

L = 4.7μH then IOUTP = 117mA and IOUTN = 105mA.

Note: The 155mA (Typ) current limit of the output dis-

connect PMOS (see Electrical Characteristics) may limit

maximum IOUTP unless CAPP is shorted to VOUTP. See

Improving Boost Converter Efficiency.

Maximum Slew Rate: Lower inductance causes higher

current slew rates which can lead to current limit over-

shoot. Choose an inductance higher than LMIN to limit

the overshoot:

LMIN = VIN(MAX) • 0.2µH

where VIN(MAX) is the maximum input voltage. Using the

previous example VIN = 3V, LMIN = 0.6μH.

Capacitor Selection

The small size and low ESR of ceramic capacitors makes

them suitable for most LT3582 series applications. X5R

and X7R types are recommended because they retain their

capacitance over wider voltage and temperature ranges

than other types such as Y5V or Z5U. A 4.7μF input capaci-

tor and a 2.2μF-10μF output capacitor are sufficient for

most LT3582 series applications. Always use a capacitor

with a sufficient voltage rating. Many capacitors rated at

2.2μF to 10μF, particularly 0805 or 0603 case sizes, have

greatly reduced capacitance at the desired output voltage.

Generally a 1206 capacitor will be adequate. A 0.22μF to

1μF capacitor placed on the CAPP node is recommended

to filter the inductor current while the larger 2.2μF to 10μF

placed on the VOUTP & VOUTN nodes will give excellent

transient response and stability. Avoid placing large value

capacitors (generally > 6.8μF) on both CAPP and VOUTP.

This configuration can be less stable since it creates two

poles, one at the CAPP pin and the other at the VOUTP

pin, which can be near each other in frequency. Table 4

shows a list of several capacitor manufacturers. Consult

the manufacturers for more detailed information and for

their entire selection of related parts.

Table 4: Ceramic Capacitor Manufacturers

MANUFACTURER PHONE

URL

Kemet

408-986-0424 www.kemet.com

Murata

814-237-1431 www.murata.com

Taiyo Yuden

408-573-4150 www.t-yuden.com

TDK

847-803-6100 www.tdk.com

Diode Selection

Schottky diodes, with their low forward voltage drops

and fast switching speeds, are recommended for use with

the LT3582 series. The Diodes Inc. B0540WS is a very

good choice in a small SOD-323 package. This diode is

rated to handle an average forward current of 500mA and

performs well across a wide temperature range. Schottky

diodes with very low forward voltage drops are also avail-

able. These diodes may improve efficiency at moderate

and cold temperatures, but will likely reduce efficiency

at higher temperatures due to excessive reverse leakage

currents.

3582512f

19

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