What am I doing wrong with this MCP1700t.

[DirtyLude]

I'm not new to regulators. I've been doing this for a while, but I got these tiny MCP1700t 5v regulators in SOT23 package and they aren't working for me.

MCP1700

I put them on my circuit board and they are just piping whatever input voltage I'm putting in straight to the output pin. No regulation whatsoever. I thought it might have something to do with the board, so I just soldered wire onto one and tested it on a breadboard, but I get the same thing. So, I've tested 2 of them with the same result.

Input is the single top lead, then on the bottom it's ground on the left and regulated output on the right. It's just not that complex, but it's not working. I put in 13v and I get 13v out. I don't have any bypass capacitors on the breadboard, but on my circuit board I had a 4.7uf input and 0.1uf output capacitor.

The full part number is MCP1700T-5002E/TT. I checked the package labeling itself and it is labeled as the 5v regulator.

I'm hoping I'm just doing something stupid, because I'm stumped here. If nobody can figure this out, I can take pictures of exactly how I have it connected. I've gone over the connections against the datasheet about a dozen times now, though.

 

[eng1]

That's an LDO regulator suitable for low input voltages only. Check the absolute maxmum ratings and the input operating voltage on the datasheet, it must be less than 6.0 V.
Have you tried with Vin = 5.5 V for example?

 

[DirtyLude]

Oh man, that's it. No. I haven't tried it with 5.5 or 6. I'm using it, because I saw it in a similar circuit, which must have had a lower input voltage. Thanks. I knew it was something stupid on my part. Time to look for another regulator. I hardly ever work with 5v, it's usually 3.3v.

 

[audioguru]

How many volts more than its max input of 6V did you feed it?
Didn't you read its datasheet?

 

[DirtyLude]

I did not read all the specs on the datasheet obviously. It's an LDO regulator, I expected it to handle more than 1 volt over the voltage it's supposed to regulate otherwise it's not all that useful, and it's not. It looks like it would be more useful in it's lower voltage parts, but regulating 6v down to 5v doesn't help me.

I only gave it 5.2 volts on the actual circuit, but it was exhibiting other strange behavior which is why I took it off to test it individually. On the breadboard I connected it straight to a walwart, which gave me something like 13v-14v. On the circuit, I expect it to handle voltages up to 12 volts, though, so I'll switch parts.

It's not a big deal. I bought 3 of them, thats $1.50 down the drain. I'll move to the LD1117.

 

[eng1]

I only gave it 5.2 volts on the actual circuit, but it was exhibiting other strange behavior which is why I took it off to test it individually.

The 0.1 uF output capacitor might have been the problem. This value is too low for proper operation.
The choice of the output capacitor is critical with LDO regulators.
The MCP1700 needs a 1.0 uF output capacitor with an ESR of 0 to 2 ohms.

 

[DirtyLude]

The 0.1 uF output capacitor might have been the problem. This value is too low for proper operation.
The choice of the output capacitor is critical with LDO regulators.
The MCP1700 needs a 1.0 uF output capacitor with an ESR of 0 to 2 ohms.

It was not the problem, but thanks. I plan to use a 1uf capacitor in the final design, but I don't have any at the moment. I was just going to desolder and solder the new one on once it arrived. I thought that the capacitors only effected the stability, which is not the problem I was seeing. The problem ended up being that I had cut a ground plane in half doing a cut into the board to mount a larger external component. I had to use a bridge wire to fix it.

In fact I made several mistakes on this board, which has caused me to rework and swap components for a new design, which is unusual for me; usually I'm pretty good at getting everything first try. It's been about a year since I've done any electronics works, though.