18-12-2012, 01:58 PM
An Area and Power-Efficient Analog Li-Ion Battery Charger Circuit
An Area and Power-Efficient Analog.pdf (Size: 552.82 KB / Downloads: 44)
Abstract—
The demand for greater battery life in low-power
consumer electronics and implantable medical devices presents
a need for improved energy efficiency in the management of
small rechargeable cells. This paper describes an ultra-compact
analog lithium-ion (Li-ion) battery charger with high energy
efficiency. The charger presented here utilizes the tanh basis
function of a subthreshold operational transconductance amplifier
to smoothly transition between constant-current and
constant-voltage charging regimes without the need for additional
area- and power-consuming control circuitry. Current-domain
circuitry for end-of-charge detection negates the need for precision-
sense resistors in either the charging path or control loop.
We show theoretically and experimentally that the low-frequency
pole-zero nature of most battery impedances leads to inherent
stability of the analog control loop. The circuit was fabricated
in an AMI 0.5- m complementary metal–oxide semiconductor
process, and achieves 89.7% average power efficiency and an end
voltage accuracy of 99.9% relative to the desired target 4.2 V,
while consuming 0.16 mm