LM2750

Switched-

Capacitor

Doubler

Ideal Linear

Regulator

Power Model

)

I

I

2

(

V

I

V

P

P

E

Q

OUT

IN

OUT

OUT

IN

OUT

˜

u

u

LM2750

www.ti.com

SNVS180L – APRIL 2002 – REVISED MAY 2013

conversion. In an ideal linear regulator, the current into the circuit is equal to the current out of the circuit. The

principles of power conservation mandate the ideal input current of a voltage doubler must be twice the output

input current which, when combined with the other input and output parameter(s), yields the following equation

for efficiency:

Comparisons of LM2750 efficiency measurements to calculations using the above equation have shown the

equation to be a quite accurate approximation of actual efficiency. Because efficiency is inversely proportional to

input voltage, it is highest when the input voltage is low. In fact, for an input voltage of 2.9V, efficiency of the

voltages, efficiency drops dramatically. In Li-Ion-powered applications, this is typically not a major concern, as

the circuit will be powered off a charger in these circumstances. Low efficiency equates to high power dissipation,

however, which could become an issue worthy of attention.

Power dissipation increases with increased input voltage and output current, up to 772mW at the ends of the

amount power/heat so the LM2750 does not overheat is a demanding thermal requirement for a small surface-

mount package. When soldered to a PCB with layout conducive to power dissipation, the excellent thermal

properties of the WSON package enable this power to be dissipated from the LM2750 with little or no derating,

even when the circuit is placed in elevated ambient temperatures.

Figure 15. LM2750 Model for Power Efficiency and Power Dissipation Calculations

LAYOUT RECOMMENDATIONS

A good board layout of the LM2750 circuit is required to achieve optimal assembly, electrical, and thermal

dissipation performance. Figure 16 is an example of a board layout implementing recommended techniques. For

more information related to layout for the WSON/SON package, see TI's AN-1187 Application Report

(SNOA401). Below are some general guidelines for board layout:

•

connections are most critical: run short traces from the LM2750 pads directly to these capacitor pads.

•

Connect the ground pins of the LM2750 and the capacitors to a good ground plane. The ground plane is

essential for both electrical and thermal disspation performance.

•

For optimal thermal performance, make the ground plane(s) as large as possible. Connect the die-attach pad

(DAP) of the LM2750 to the ground plane(s) with wide traces and/or multiple vias. Top-layer ground planes

are most effective in increasing the thermal dissipation capability of the WSON package. Large internal

ground planes are also very effective in keeping the die temperature of the LM2750 within operating ratings.

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