9

LTC3413

sn3413 3413fs

dielectrics have the best temperature and voltage charac-

teristics of all the ceramics for a given value and size.

Output Voltage Programming

The output voltage will be equal to one-half of the voltage

V

V

OUT

REF

=

2

If a different output voltage relationship is desired, an

output voltage will then be set according to the following

equation:

pulled above 2V. The full current range becomes available

with a resistor and capacitor on the RUN/SS pin as shown

in Figure 1a. The soft-start duration can be calculated by

using the following formula:

tR

VV

SS

SS

IN

=









• C

ln

V

(Seconds)

SS

IN

–.

18

Efficiency Considerations

The efficiency of a switching regulator is equal to the

output power divided by the input power times 100%. It is

often useful to analyze individual losses to determine what

is limiting the efficiency and which change would produce

the most improvement. Efficiency can be expressed as:

Efficiency = 100% - (L1 + L2 + L3 + ...)

where L1, L2, etc. are the individual losses as a percentage

of input power.

Although all dissipative elements in the circuit produce

losses, two main sources usually account for most of the

dominates the efficiency loss at medium to high load

currents. In a typical efficiency plot, the efficiency curve at

very low load currents can be misleading since the actual

power lost is of no consequence.

the DC bias current as given in the Electrical Characteris-

tics and the internal main switch and synchronous switch

gate charge currents. The gate charge current results from

switching the gate capacitance of the internal power

MOSFET switches. Each time the gate is switched from

APPLICATIO S I FOR ATIO

R2

R1

3413 F02

SGND

LTC3413

Figure 2. Setting the Output Voltage

V

VR

R

OUT

REF

=+









2

1

2

1

Soft-Start

The RUN/SS pin provides a means to shut down the

LTC3413 as well as a timer for soft-start. Pulling the

RUN/SS pin below 0.5V places the LTC3413 in a low

The LTC3413 contains an internal soft-start clamp that