MULTI-LEVEL SWITCH ARRAY.

In order to supply high load currents across the entire V

IN

operating range, especially at lower V

charge pump are normally designed to have low on-

resistance. However at high input voltages and low load

currents, this low resistance results in high output voltage

ripple due to the output capacitor being charged too quickly.

To solve this problem, while still being able to deliver the

needed output current, the LM2753 has a switch array with

multiple switches connected in parallel.

The number of switches used in parallel depends on the

input voltage applied to the LM2753. At lower input voltages

all paralleled switches are used, and as the input voltage

rises, switches are removed from the parallel configuration.

The highest switch resistance is achieved as the input volt-

age reaches the maximum operating voltage, which helps

with voltage management.

THERMAL PROTECTION

When the junction temperature exceeds 140˚C (typ.), the

LM2753 internal thermal protection circuitry disables the

part. This feature protects the device from damage due to

excessive power dissipation. The device will recover and

operate normally when the junction temperature falls below

125˚C (typ.). It is important to have good thermal conduction

with a proper layout to reduce thermal resistance.

POWER EFFICIENCY

Charge-Pump efficiency is derived in the following two ideal

equations (supply current and other losses are neglected for

simplicity):

I

E=(V

In the equations, G represents the charge pump gain. Effi-

ciency is at its highest asGxV

the efficiency graph in the Typical Performance Character-

istics section for the detailed efficiency data.

POWER DISSIPATION

The power dissipation (P

ture (T

is the product of the input current and input voltage, P

the power consumed by the load connected to the output,

T

θ

ambient thermal resistance for the LLP-10 package. V

the input voltage to the LM2753, V

output of the device, and I

the load(s) connected to both V

P

=(V

T

θ

The junction temperature rating takes precedence over the

ambient temperature rating. The LM2753 may be operated

outside the ambient temperature rating, so long as the junc-

tion temperature of the device does not exceed the maxi-

mum operating rating of 120˚C. The maximum ambient tem-

perature rating must be derated in applications where high

power dissipation and/or poor thermal resistance causes the

junction temperature to exceed 120˚C.

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