Boost regulator

[Tom120]

I have a project with a step up dc/dc converter. It is a ltc3400 chip. At the moment it is working fine 2v to 4v but it seems to stop working down at 1.5v input.( The spec is 0.85v minimum input). I was wondering if anyone knows any problems that might occur as the input voltage is reduced.

 

[danadak]

Is your battery capable of delivering energy at 1.5V ? What is your energy source ?


Regards, Dana.

 

[Tom120]

Hi Dana. Yes I'm using a 1.5v battery in good condition.(Tom)

 

[Tony Stewart]

What deviations to the App Note such as figure 2 and the values did you make? and why?
https://www.analog.com/media/en/technical-documentation/data-sheets/3400fa.pdf

 

[sagor1]

What is the load? Note that in the spec sheet (Minimum Start-Up Voltage vs Load Current), if the load is around 100mA, the startup voltage required is around1.3V

 

[Tom120]

Thanks for replying. My circuit differs from the app example only in resistors R1 and R2. R1 is 1.5M and R2 is 620K to produce 4.2v output. I've been testing the circuit with a light load - about 1mA.

 

[tepalia02]

Thanks for replying. My circuit differs from the app example only in resistors R1 and R2. R1 is 1.5M and R2 is 620K to produce 4.2v output. I've been testing the circuit with a light load - about 1mA.

Have you performed any tests in no load condition?

 

[Tom120]

Yes. Same result with zero load. (4.2 volts with 2volt input but only 1.2 volts with 1.5 volt input)

 

[rjenkinsgb]

The data sheet mentions the extra Schottky diode is used for the graph showing 1.5V operation.

Also, due to the high operating frequency the type of capacitors may be critical - try adding 0.1uF ceramics across the input & output caps??

 

[Tom120]

Thanks for that. I tried the extra caps also the schottky diode but no change unfortunately.

 

[Lightium]

You should have a cap across the source voltage when using anything on its low voltage end.

 

[rjenkinsgb]

Thanks for that. I tried the extra caps also the schottky diode but no change unfortunately.

How is the circuit built? If there are long connections between any components in the high frequency current path, that could affect efficiency?

 

[Lightium]

Without a pic or schematic it's tuff to tell what's drawing all the current.

 

[Tom120]

Hi. Just thought I'd let you know the result of this one. Later I read that overheating the chip through careless soldering might degrade performance. I got another LTC3400 and soldered it carefully. This time the circuit worked fine. All the way down to 0.8volt input producing a 4 volt output. (Tom120)