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Switcher vs. LDO for automotive applications?

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blapcb

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OK, so I have just finished a prototype (for automotive) using the L5790D switcher. But, now I am confused.... because, it is suggested (by some), that LDOs are also fine for this application and are actually a lot less expensive and less part count also. So... what are the pros and cons of Switchers vs. LDOs?
In my case, the application is an automotive telematics unit (GPS/GSM) for 12/24v cars/trucks. Thanks!
 

emresel

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LDOs are less energy efficient means it may be heat up. In your applicaiton if you obtain i.e. 3v3 volts from 12v, and ie 250mA, you consume (12-3.3)*0.25=2.175 Watts on LDO. It is case may be too hot depending on ambient temperature, package, PCB design etc...
On the other hand since it is not switching, there is no swtiching noise on supply line. That means a clean supply. It may be important depending on application. If you are suppliying an RF receiver cct, it is better LDO regulated clean supply to have a better reception performance.
 

mister_rf

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To choose an optimal solution we need to consider also the maximization of efficiency, taking into account the current consumption of the equipment.
To minimize noise in power lines is necessary to use additional filters, including capacitors with minimal series inductance, like ceramic capacitors, solid tantalum capacitors or the newest solid polymer aluminum (SPA) type.
 

blapcb

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OK I was going to post another thread on this but see that I already had started this one a while back :)
So....

Can someone please elaborate on how to go about deciding if I should use a switcher or an LDO?
As I said I presently use a L5970D switcher. But why not use a LM317 for example that is robust and wide input?
The application is automotive telematics meaning a GSM module that will also draw peaks of 2A at about 200Hz.

Thanks
 

dick_freebird

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It probably all comes down to waste heat. Calculate the power
dropped in a linear regulator (VBATmax-Vload)*Iload and if it's
over a couple of watts, you're past underdash convection cooling
as an option.
 

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