LT3483

7

3483fb

APPLICATIONS INFORMATION

it to around twice the value recommended, as too large

of an inductance will increase the output voltage ripple

without providing much additional output current.

Table 1. Recommended Inductors

PART

L

(μH)

MAX

(mA)

DCR

(Ω)

HEIGHT

(mm)

MANUFACTURER

LQH2MCN4R7M02L

LQH2MCN6R8M02L

LQH2MCN100M02L

4.7

6.8

10

300

255

225

0.84

1.0

1.2

0.95

Murata

www.murata.com

SDQ12

Coupled

Inductor

10

15

980

780

0.72

1.15

1.2

Cooper Electronics

Tech

www.cooperet.com

744876

Coupled

Inductor

10

550

0.46

1.2

Würth Elektronik

www.we-online.com

Capacitor Selection

The small size and low ESR of ceramic capacitors make

them ideal for LT3483 applications. Use of X5R and X7R

types is recommended because they retain their capaci-

tance over wider voltage and temperature ranges than

other dielectric types. Always verify the proper voltage

rating. Table 2 shows a list of several ceramic capaci-

tor manufacturers. Consult the manufacturers for more

detailed information on their entire selection of ceramic

capacitors.

ommended where the distance to the power supply or

battery could be more than a couple inches. Otherwise,

a 1μF is adequate.

A capacitor in parallel with feedback resistor R1 is recom-

mended to reduce the output voltage ripple. Use a 5pF

capacitor for the inverting charge pump, and a 22pF value

for the inverting flyback or other dual inductor configura-

tions. Output voltage ripple can be reduced to 20mV in

some cases using this capacitor in combination with an

appropriately selected output capacitor.

The output capacitor is selected based on desired output

voltage ripple. For low output voltage ripple in the inverting

flyback configuration, use a 4.7μF to 10μF capacitor. The

inverting charge pump utilizes values ranging from 0.22μF

to 4.7μF. The following formula is useful to estimate the

output capacitor value needed:

2

in the inverting charge pump configuration ranges from

0.1μF to 0.47μF. Multiply the value predicted by the above

for the flying capacitor.

Table 2. Recommended Ceramic Capacitor Manufacturers

MANUFACTURER

URL

AVX

www.avxcorp.com

Kemet

www.kemet.com

Murata

www.murata.com

Taiyo Yuden

www.tyuden.com

Setting the Output Voltage

The output voltage is programmed using one feedback

resistor according to the following formula:

R1= –

10μA

Inrush Current

an inrush current will flow through the input inductor and

integrated Schottky diode to charge the flying capacitor.

Conditions that increase inrush current include a larger,

and an inductor with a low saturation current.

While the internal diode is designed to handle such events,

the inrush current should not be allowed to exceed 1.5A.

For circuits that use flying capacitors within the recom-

mended range and have input voltages less than 5V, inrush

current remains low, posing no hazard to the device. In

should be measured to ensure operation within the limits

of the device.