Hi,i am using TPS76918 voltage regulator and i noticed that it requires low esr capacitors at the output.What does it mean and what kind of capacitors i have to use?With what specifications?

 

There's no real "standard" regarding what can be called low ESR, all you can do is believe what they claim.

They're probably trying to keep you away from just putting a 0.1 uF or something on the output.

I notice they recommend a 4.7 uF with a maximum ESR or 0.2 ohms. Those shouldn't be hard to find, or you can just use a slightly larger cap to meet the ESR requirements.

 

Just about anything you buy new.

Tantalum caps and even ceramic caps are low-esr.

Electrolytic caps have the highest esr that I know of, and you can find special marked "LOW-ESR" electrolytic caps.

If you are using the caps for decoupling and/or to prevent oscillation, ceramic will be just fine.

 

Sometimes low ESR capacitors are called low impedence.

If you are using ceramic capacitors, the ESR for ceramic caps is usually so small it can be neglected. If you are using electrolytic capacitors, it is important.

The line is blurred between low ESR and normal caps - there is no definite point at which a capacitor is low ESR or not.

A low ESR capacitor basically means the capacitor has low equivalent series resistance. Think of a parasitic resistor in series with the cap. If you try and draw current from the capacitor, this resistor produces heat. It also increases ripple voltage.

 

Here is a link to information about ESR - http://wiki.xtronics.com/index.php/Capacitors_and_ESR

You can look for the caps using a search engine - http://www.vishay.com/capacitors/low-esr/ or you can look at a catalog listing and pay attention to the ESR figure - http://search.digikey.com/scripts/DkSearch/dksus.dll?Cat=131081

 

Yea, you can enter the ESR as a filter in Mouser's drill down selection database too.

Remember that you're working with low voltages, the selection of leaded electrolytics in that area have dwindled but you can find about anything in surface mount.

They list several options in the datasheet as acceptable:
http://focus.ti.com/lit/ds/symlink/tps76918.pdf

 

You can also put a ceramic (say 0.1 uF) in parallel with an electrolytic of 4.7 uF to have a similar effect as a low esr capacitor of 4.7 uF. A lot of datasheets will show multiple capacitors in parallel instead of a single larger one.

John

 

I notice they recommend a 4.7 uF with a maximum ESR or 0.2 ohms. Those shouldn't be hard to find, or you can just use a slightly larger cap to meet the ESR requirements.

They recommend a minimum ESR of 0.2 ohms, and a maximum of 10 ohms.

This is typical of low dropout regulators--the ESR can't be too low.

 

They recommend a minimum ESR of 0.2 ohms, and a maximum of 10 ohms.

This is typical of low dropout regulators--the ESR can't be too low.

Exactly right. Use a cheapo electrolytic.

 

They recommend a minimum ESR of 0.2 ohms, and a maximum of 10 ohms.

This is typical of low dropout regulators--the ESR can't be too low.

Gotcha, need some sort of impedance o the circuit.

 

These app notes discuss the problem:

http://focus.ti.com.cn/cn/lit/an/slva115/slva115.pdf

http://www.ti.com/lit/an/snva167a/snva167a.pdf