Is this the current limiting?

[EDA_hg81]

When smart card reader is doing reading function, the voltage at node 1 dropped to 4V but after reading the voltage is back to normal 5V.

Do you think it is current limiting?

Under what condition switching regulator LM2736 can lose voltage regulation?

By the way, what “Contact electrical data” means?

Thank you so much.

 

[JoannesPaulus]

current limiting could definitely be the reason. The regulator can stop working when the output current is too high.

 

[EDA_hg81]

Please correct me if I am wrong.

Since the voltage only dropped to 4V from 5V, this means the LM2736 is still working properly to regulate the output voltage.

 

[JoannesPaulus]

No, that's incorrect. The regulation voltage is 5V, if it drops below that it is not regulated anymore!

 

[karesz]

Hi,
Is it some older equipment pls?
C1/2 are 10/22uF ceramics & trough thermocycling is possible, that the capacitance lossed_especially C2/22uF!
I would change C2(ev. L1 too & IC as last), but are you sure, that your load is in specifications range?
Your LDO should be capable to deliver up to 0.7A...
Did you measured the input voltage if reader is working_maybe it isnot 9V:-(
K.

 

[dick_freebird]

What about the 9V source impedance?

Begin with measuring all the intermediate voltages and see
where the load-droop begins to appear, in the chain.

 

[bill66656]

Look for the current limit threshold value and then calculate your application peak current, to see if they are close.

 

[umesh49]

Check this link, might be useful
**broken link removed**