Global Sources
EE Times-India
Stay in touch with EE Times India
EE Times-India > T&M

Solutions for LDO load transient improvement

Posted: 18 Nov 2008     Print Version  Bookmark and Share

Keywords:low dropout  error amplifier  LDO design  load transient 

The low dropout (LDO) regulator is widely used in many portable electronics systems such as cell phones, notebooks and PDAs. In these mobile devices, LDO design is challenging due to the need for reduced power consumption and accurate operation.

As the digital circuit—which is supplied from the LDO output—switches from one mode of operation to another, the load demand on the LDO can change quickly. This quick change of load results in a temporary glitch of the LDO output voltage. But digital circuits do not react favourably to large voltage variations. This makes LDO load transient improvement very important.

Using the conventional LDO structure, which includes an error amplifier and a pass device, it is possible to define the influence of the load variation on LDO operation.

Variation of LDO load current changes LDO output voltage level until the error amplifier will be able to compensate for the variation by driving the pass transistor according to the variation of the load current. There is always a delay between output current changing and reaction of the error amplifier. During this time voltage spikes at the LDO output are created. By reducing the delay time it is possible to minimise the output voltage error. This delay time has many causes. One of the main causes is the time needed for charging the parasitic capacitance of the pass device. LDOs that are usually used in portable applications have a maximum output current in a range of a few hundred milliamps. This requirement increases the pass device area. Thus parasitic capacitances Cp1 and Cp2 of the pass device also increase and can exceed 100pF. This affects power consumption, and battery life extension is very important nowadays.

View the PDF document for more information.

Comment on "Solutions for LDO load transient imp..."
*  You can enter [0] more charecters.
*Verify code:


Visit Asia Webinars to learn about the latest in technology and get practical design tips.


Go to top             Connect on Facebook      Follow us on Twitter      Follow us on Orkut

Back to Top