LTC3414

11

3414fb

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 characteristics

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

high to low to high again, a packet of charge dQ moves

are the gate charges of the internal top and bottom

switches. Both the DC bias and gate charge losses are

nounced at higher supply voltages.

tinuous mode the average output current flowing through

inductor L is “chopped” between the main switch and the

synchronous switch. Thus, the series resistance looking

into the SW pin is a function of both top and bottom

obtained from the Typical Performance Characteristics

multiply the result by the square of the average output

current.

losses and inductor core losses generally account for less

than 2% of the total loss.

Thermal Considerations

In most applications, the LTC3414 does not dissipate

much heat due to its high efficiency.

However, in applications where the LTC3414 is running at

high ambient temperature with low supply voltage and

high duty cycles, such as in dropout, the heat dissipated

may exceed the maximum junction temperature of the

part. If the junction temperature reaches approximately

150

°C, both power switches will be turned off and the SW

node will become high impedance.

To avoid the LTC3414 from exceeding the maximum

junction temperature, the user will need to do some

thermal analysis. The goal of the thermal analysis is to

determine whether the power dissipated exceeds the

maximum junction temperature of the part. The tempera-

ture rise is given by:

is the thermal resistance from the junction of the die to the

ambient temperature. For the 20-lead exposed TSSOP

package, the

Note that at higher supply voltages, the junction tempera-

To maximize the thermal performance of the LTC3414, the

exposed pad should be soldered to a ground plane.

Checking Transient Response

The regulator loop response can be checked by looking at

the load transient response. Switching regulators take

several cycles to respond to a step in load current.

amount equal to

overshoot or ringing that would indicate a stability prob-

tor shown in Figure 1 will provide adequate compensation

for most applications.

APPLICATIO S I FOR ATIO