LT3461/LT3461A

6

3461af

Inductor Selection

The inductors used with the LT3461/LT3461A should

have a saturation current rating of 0.3A or greater. If the

device is used in an application where the input supply will

be hot-plugged, then the saturation current rating should

be equal to or greater than the peak inrush current. For the

LT3461, an inductor value between 10µH and 47µH,

depending upon output voltage, will usually be the best

choice for most designs. For the LT3461A, inductor values

between 4.7µH and 15µH inductor will suffice for most

applications. For best loop stability results, the inductor

value selected should provide a ripple current of 70mA or

with LT3461A is estimated by the formula:

L (in microhenries) =

DV

V

AV

IN

OUT

•

•

• sec

•

1

11

+

+

VV

V

VV

OUT

IN

OUT

1

1

–

Use twice this value for the LT3461.

Capacitor Selection

Low ESR capacitors should be used at the output to

minimize the output voltage ripple. Multilayer ceramic

capacitors using X5R/X7R dielectrics are preferred as they

have a low ESR and maintain capacitance over wide

voltage and temperature range. A 2.2µF output capacitor

is sufficient for most applications using the LT3461, while

a 1µF capacitor is sufficient for most applications using

the LT3461A. High output voltages typically require less

capacitance for loop stability. Always use a capacitor with

sufficient voltage rating.

Either ceramic or solid tantalum capacitors may be used

for the input decoupling capacitor, which should be placed

as close as possible to the LT3461/LT3461A. A 1µF

capacitor is sufficient for most applications.

Phase Lead Capacitor

A small value capacitor can be added across resistor R1

between the output and the FB pin to reduce output

perturbation due to a load step and to improve transient

response. This phase lead capacitor introduces a pole-

zero pair to the feedback that boosts phase margin near

the cross-over frequency. The following formula is useful

to estimate the capacitor value needed:

C

k

R

pF

Ω

500

2

1

•

For an application running 50µA in the feedback divider,

capacitor values from 10pF to 22pF work well.

APPLICATIO S I FOR ATIO

TYPICAL APPLICATIO S

Figure 4. 5V to 12V with Soft-Start Circuit (LT3461A)

Input Current and Output Voltage

5V

L1

10µH

R1

261k

R2

30.1k

C2

1µF

15pF

C1

1µF

12V

70mA

1

2

SW

3

4

5

6

FB

SHDN

GND

LT3461A

3461a TA02a

CONTROL

SIGNAL

47nF

47k

C1, C2: TAIYO YUDEN EMK212BJ105

L1: MURATA LQH32CN100K53

50mA/DIV

CONTROL

SIGNAL

5V/DIV

1ms/DIV

5V/DIV

3461a TA02b