POWER ELECTRON C DIFFERENT LDO TYPES AND THE


VARIOUS OPTIONS IN TOPOLOGY Hans Adams, manager at Ricoh Europe Semiconductor support centre highlights the different types of LDO regulators, which are available today and the possibilities of combining the features of two LDO types, and how to optimise the capabilities


advanced processors with a high operating frequency, as a result the load of the voltage regulator contains fast load transient peaks. First of all, the regulator should be able to regulate fast enough in order to compensate the over and undershoot peaks.


T


Secondly, certain applications are in a standbymodemost of the time and only active for a short period. In such cases the current consumption should be kept low during the standby period as much as possible to extend battery life. In the last years LDO’s experienced an


conversion (less heat dissi devices have amore effici DC/DC Converters,mainly increasing competition of


available (Buck, Boost, Bu


because such advanced


ent power


there are various options i compared to voltage regu


lators and also pation)


ck-Boost etc.). n topology


However, there are still plenty of advantages left to choos e for a CMOS LDO regulator:


 Power supply <2A and moderate Vin versus V


 Cheap and simple soluti  Only two external comp  Ultra small PCB area outdifference


 High ripple rejection  Low output noise


 Low supply curren t CURREN CONSUMP ION CURRENT CONSUMPTION:


With LDO current consumption we actually mean the supply quiescent current or grou


nd current of current,


the LDO required to provide power to internal circuits plus the current


flowing through the resistor divider on the output in order to set and measure the output voltage.


Another feature important for an LDO is the dynamic performance, which is the ability to respond to line peaks (fluctuations of the inpu t voltage) and load peaks (fluctuations of the output current) as well as the performance to attenuate any ripple on the input voltage.


LDO CATEGORIESATEGORIES


• LDOs with low current consumption • LDOs with high dynamic performance


/ ELECTRONICS ELECTRONICS


onents on


• LDOs with selective performance • LDOs with seamless performance


LDO W TH L


LDO WIITH LOW CURREN CONSUMP ON


CONSUMPTIION Traditional LDOs have a relatively


constant low current consumption level with respect to the output current range. Their main disadvantage is a moderate dynamic performance, such as load and line transient response, ripple rejection or output noise. These devices are optimised to prolong the lifetime of battery powered applications with less demanding performance requirements. Supply currents are ranging from around 0.2 to 10µA. The current trend is to develop new LDO products with a current consumption belo w 1µA .


HIGHIH GH DYNAM C PERFORMANCE LDOs with good dynamic performance are very well suited for applications


NAMICI PERFORMANCE Figure 1: Figure 1:


CMOS LDOs a e available in varavailable in variousious packages


Os arer packages CURRENT Figure 1: Figure 1:


Comparison of the O types


Comparison of the various Lrva ious LDO types


oday’s applications contain


demanding a fast response speed high ripple rejection and low output noise. However, in order to provide such high performance these LDOs require more power for the internal control circuit. Supply currents are ra around 20 to 250µA. One may prefer to h


,


combination of the previously two described LDOs. These products exist and have the possibili between two internal one optimised for low consumption and the


other one for current


good dynamic performance. An


additional ECO pin switches between the internal control circuits whilst another CE pin disables the LDO. The main advantage of this type of LDO is that high current consumption only occurs when required.


The first generation of these selective performance LDOs had a manual switching mechanism to switc h between modes. This requires


additional control software and wiring on the circuit board. For this particular reason a new product was developed with an automatic switching


mechanism. As soon as the output current demand is high enough, the LDO will switch over to another mode and vice versa. This current threshold is


few milliamps. Typic a internally fixed and is


l for these type o f in the range of a


LDOs is the fact that they have two levels of current consumption. Further development on LDO’s


resulted in a new generation, the so called seamless LDO. Instead of a fixed output current threshold to switch between modes, this type improves the dynamic performance significantly at higher output current demands. Consequently, it operates similar to a high performance LDO. The current consumption will increase


proportionally with the performance, at no load it has a typical value in the range of 10µA.


Ricoh Europe www.ricoh-europe.com


www.ricoh-europe.com e: cco@ricoh-europe.com


ELEC ELECTRONICS | DECEMBER/JANUAR ECEMBER/J JANUARY 2017 23 23


control circuits , ty to switch


ONICI S


FEAT RE FEA ATURE


ave an LDO with a nging from


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