Step-Down Charge Pumps Are Tiny, Efficient
and Very Low Noise – Design Note 310
William Walter
Introduction
Inductorless charge pump DC/DC converters are popular
in space-constrained applications with 10mA to 500mA
load currents. Such converters are available in small
packages, operate with very low quiescent current and
require minimal external components. However, the
downside for most charge pumps is noise. Noise that
is generated at the power input can interfere with RF
transmission and reception in wireless applications, and
noise at the output can couple into sensitive circuits
or even create audible noise. The new LTCВ®3250 and
LTC3251 step-down charge pumps solve this problem
with a new switching architecture that mitigates noise
without sacrificing any of the space saving, high efficiency benefits typical of charge pump converters.
The LTC3250-1.5 is optimized for applications that require up to 250mA of current from a п¬Ѓxed 1.5V output,
and where space is at an absolute premium. The LTC3251
provides more flexibility in a slightly larger footprint:
it features an adjustable output voltage (0.9V to 1.6V),
up to 500mA output, ultralow input and output noise
and spread spectrum operation. Both ICs use 2-to-1 …