[SOLVED] LD1117S33 vs MIC5205-3.3

Hi,
I am new to the forum. I am working on a project that involves a 6volt (4 AA) battery supply and the main ICs are running on 3.3v. I have tried LD1117S33 with Caps filter as it recommended in the APP but I am getting a spike max 4v when I unhook and re-hook the battery (4 AA) at power up. Is MIC5205-3.3 LDO more stable then the LD1117S33? I am trying to get rid of the voltage spike and stay away from ferrite beads if possible. I have attached my power up circuit below.

Thanks,
Sheng

I used several year LD1117 as a regulator, and it works very well . how did you measure output? also with battery you should have very stable circuit it should be depend on your measurement. do you have load? what is it? if no use a 1k ohm resistor as load and test it again. if yes disconnect it and test it again with 1k ohm resistor as load.
also it is better to use ceramic capacitor 100NF parallel to the output of regulator .

Hi Asadi,

I am using the 3.3 Vout of the regulator to power Bluetooth smart chip (BLE112). I hook up my scope to the Vout of the regulator to do some measurement. The reason I am testing the regulator is because the BLE112 chip keep losing the store memory once I power down and re-hook the battery. During stable power, everything work great. Please look at attached waveform. The attached waveform is capture by unhook and re-hook the battery. Also, I notice in example of the BLE112 app note they used a ferrite bead and a ldo but limited to 6v max. The reason I used ld1117 is have Vin great then 6v for protection since 4AA something is greater then 6v. That's why I was wondering if MIC5205 would be a better choice for this project. Are you referring to adding an extra 100nf cap parallel to the 10uf Cap?

Thanks,
Sheng

**broken link removed**

Hi Sheng,
your attachment doesn't work.
I attached the circuit bias that I use several year without any problem.


best regards,
Siyavash.

Hi Siyavash,
I hope my attachment work this time. Please find attached the spike waveform.

From looking at your circuit, I notice a ferrite bead. What value did you use for your ferrite bead? I assume a ferrite bead is really needed to make it clean and spike free from your example.

All I needed was a circuit that used 4 AA battery to convert to a 3.3 v DC clean and smooth with out spike. Do you have any recommend circuit for my project? Will your example work?

Thanks,
Sheng


**broken link removed**

I used this circuit for more than 50 board and they work very well, so my recommended circuit was what I attached for you.
120 ohm ferriteberad is suitable.
no, your attachment doesn't work again.
best regards,
Siyavash

Hi Siyavash,

Great I will give your circuit a try. How is the value for the ferritebead calculated?

Thanks again,
Sheng

1uH is suitable.