So im trying to explore this part. LT8331

DigiKey Link here

On the digi key site there is a ltspice download of a simulation for the part. I can get that to run.
However, the part is suppose to be capable of a negative output voltage.

According to the datasheet, i just have to follow this equation and it should output a negative voltage but its not.

R1 = R2* (abs(vout)/.8 - 1)

I have not been able to get it to output a negative voltage. Can someone help me?

Model attached

 

The datasheet shows on page 26 voltage converters with a negative output voltage.

 

The datasheet shows on page 26 voltage converters with a negative output voltage.

Hi, thanks for your reply
I have duplicated the circuit on page 26 and the voltage is still not -12?
I dont get it

 

hi mike
post your asc circuit for page 26
E

 

hi mike
post your asc circuit for page 26
E

Here is what i have

 

I know its not exact, its based on the spice model from digi key. Its just missing the second inductor but that should only effect its stability and ripple i imagine not the fact that its outputting 24+ instead of -12
I must be missing something obvious

 

Hi mike,
To save me from drawing out the circuit, please post the asc file
E

 

Hi mike.
Your circuit is nothing like the one/s on page 26???
E

 

I have modified to make it look exactly like the picture. I am getting a crazy oscillation

 

The only thing that was not the same was C2 and i just madeit 22uF and it didnt seem to change to much

 

Hi mike,
This is a version of page 26


You are missing the K1 mutual coupling factor.
E

 

Hi mike,
This is a version of page 26
E
View attachment 301723

Thats not right either, Look at your bias pin. It should be going to ground.

Also it says it operates down to 5V input. Which is what im trying.

 

Hi mike,
This is a version of page 26


You are missing the K1 mutual coupling factor.
E
View attachment 301723

Also your D2 and C2 are not in the same config

 

Also your D2 and C2 are not in the same config

Scartch this, it is.
Mine still is not working though. I literally duplicated yours and get a different result

 

Hi mike,
This is a version of page 26


You are missing the K1 mutual coupling factor.
E
View attachment 301723

Can you send me your .asc?

 

What D2 and C2?

Your sim is missing K1 L1 L2 1

 

ok i dont get it. For whatever reason mind just started working. The only thing i did was give D1 and C2 a separate ground instead of tieing them to a single ground

 

What D2 and C2?

Your sim is missing K1 L1 L2 1

The sepearte grounds worked





Does not work.

With the grounds at the same node.....
I dont get it??????

 

What D2 and C2?

Your sim is missing K1 L1 L2 1

What do you mean missing? I have L1 and L2?

 

As requested. Please post your asc file, so that we can all sing from the same hymn-sheet.