Output capacitor selection for LD1085D2M-R

[hamzdmr]

Edited by a ST moderator: Update the title and the content with the part number

Hi,
I'm using LD1085D2M-R regulator. There is no certain information about output capacitor ESR limit value for stabilization. 

-Input : 5V

-Output : 4V @3A

-Desired Output Capacitors : 2x10uF 10V 
 

Can we use Ceramic capacitors with additional series resistor? In this case what is required resistance value?

  

[mƎALLEm]

Hello,

What ST product are you using in your case?

See How to write your question to maximize your chances to find a solution

[hamzdmr]

Sorry mƎALLEm,

The IC we are going to use is LD1085D2M-R.

Best regards.

[AScha.3]

Hi.

>  Input : 5V     --> Output : 4V @3A

Anyway not possible...see dropout of LD..:  about 1.25 V

 

[RobK1]

---

@hamzdmr wrote:

There is no certain information about output capacitor ESR limit value for stabilization. 

---

There are two graphs, one for VO=1.8V and one for VO=12V. While the maximum ESR is quite different in both cases, the minimum is 0.08Ohms in both cases. That seems pretty certain to me.

[Peter BENSCH]

As @AScha.3 noted, you cannot use the LD1085D2M-R for your specification because it is a so-called quasi LDO. That is why it is not listed on our website under LDO, but under Standard voltage regulators. Although quasi LDOs achieve better dropout voltages than classic linear regulators, they were later replaced by true LDOs with dropout voltages significantly below 1V.

Instead of the LD1085, you can consider the LD29300, which remains below 400mV at 3A and can therefore easily regulate the specified output voltage of 4V.

Even though this LDO is also not designed for ceramic capacitors due to its age, you can still use ceramic caps if you add an artificial ESR of at least 300mΩ (see data sheet, fig. 14).

Hope that helps?

Regards
/Peter