When I build the circuit on the circuit breadboard. the input voltage is 1.3，but output only 2.0v without load resistance. when I input 3v with two cells batteries，the ouput only 2.8v without load. If I add load for circuit, the output voltage is lowee. So why? Is that any problem with official datasheet? Please somebody can help me?

 

The part works as advertised. I've got a few thousand of them in the field with no problems.

You're doing something wrong.

 

I find it curious that your schematic has no pin numbers on it. I hope you did not depend on your memory to remember the pin numbers that go with the names.

 

I find it curious that your schematic has no pin numbers on it. I hope you did not depend on your memory to Rember the pin numbers that go with the names.

yes,the pin numbers are right, so I'm very confused

 

Measure the current consumption without load. If it is high, replace the Cout capacitor. Also check the choke.

 

How big is your alkaline cell? What is its terminal voltage on load? Remember that it has to supply 250mA.

 

Cout might be backwards.
If it is an electrolytic the negative plate should be grounded.

 

Cout might be backwards.
If it is an electrolytic the negative plate should be grounded.

I use 10uF monolithic capacitor which are Cin and Cout

 

Are you sure that the inductor is not saturating ? What is the full specification ofthe inductor ?

Les.

 

Is it cased by breadboard ? I test is on the breadboard.

 

Are you sure that the inductor is not saturating ? What is the full specification ofthe inductor ?

Les.

Good point! It is fairly common for people to use a small signal inductor in this kind of circuit. Small signal inductors sometimes have high resistance or saturate too easily.

I will also add that those plastic breadboards often make high resistance or intermittent contact with components and jumpers.

Also, go back and re-read post #2.

 

Could be breadboard, they are notorious for bad connections - for something this simple I'd 'rats-nest' in free air! But my guess is wrong type of inductor - common mistake!

 

Is it cased by breadboard ? I test is on the breadboard.

Post pictures of your breadboard work, you might have missed something.

 

Post pictures of your breadboard work, you might have missed something.

here is the breadboard, I build it with offical circuit. I test the inductive current is about 4 mA

 

Are you sure that the inductor is not saturating ? What is the full specification ofthe inductor ?

Les.

the inductor Rdc 100 mohm，saturation current is 3A

 

The spec for the inductor looks OK. I can't read the marking on the capacitors but they look too small to be 10 uF. They look more like 10 nF ceramic capacitors. Can you post a close up of the markings on the capacitors.
I also think the capacitor and inducter should be connected to the MCP1640 with much shorter wires.

Les.

 

You should move all the components farther apart so they can be less effective.

 

they look too small to be 10 uF

Mouser lists over 90 branded 5mm dia/5mm lead spacing 10uF MLCC so its possibly OK

 

Mouser lists over 90 branded 5mm dia/5mm lead spacing 10uF MLCC so its possibly OK

Possible but they do look like the classical 104 Ceramic Capacitor 0.1uF bypass capacitor we've all used a million times.

 

this is MLCC 106(10uF) ,I think it's normal.
nsaspook,Irving,joeyd999,LesJones