LT8210 adjustable input voltage Vin

Hi Jeufi2000,

My name is Chris Gass. I am the factory application engineer supporting this part.

The LT8210 requires 4.5 VIN to start up. After the part has started and EXTVCC is connected to VOUT, the part will run to VIN of 2.8 V.

Please let me know if you have any other questions,

Chris

Hi Chris,

thx for the quick response. EXTVCC is connected to VOUT after start, but does EXTVCC connects automatically?? or do I have to make some changes on the pcb? 

I have changed the threshold Resistors already but still not have what I need.

Is it possible to have a phone call?

Jeufi2000

Hi Chris,

i have the same issue too with Vin less than 4.5

i have changed the threshold resistors already but still having 0V output by Vin less than 4V 

I also removed the R33 leaving it open while connecting CXVCC in parallel with R32 (CXVCC=4.7uF and R33=1K) still not having the output i need.

Question: is R32=RXVCC? because there is no space for RXVCC on the Board

please  how can i achieve an output voltage of 10V when my Vin is 3V?

Can you also send a circuit/drawing of how i can connect?

Thanks

Tati

Hi Tati,

Nice to meet you. 

R33 must be 0 ohms. The part is then powered from VOUT instead of VIN. VEXTVCC needs to stay above roughly 7-8 V. If it falls below this, then the part will switch back to being powered from VIN and then quit switching when VIN falls below about 4.5 V.

Please be sure to keep R33 = 0 ohms for this mode of operation.

Thank you,

Chris

Hello Chris,

Thanks for your support.

R33 was already 0  ohm but still not working. 

i am having Board B just for you to know.

Thanks

BR

Tati

Hello Chris,

Thanks for your support.

R33 was already 0  ohm but still not working. 

i am having Board B just for you to know.

and also please what is the value of R32 on the Board? should it be left open? 

is R32 same as RXVCC?

Thanks

BR

Hi Chris,

can you please provide me a block diagram how to achieve an output voltage with an input Vin >= 2.8V?

Then I tried already several thinks and changed R32 & R33 but still not have an output voltage with an input voltage lower than 4.0V.

Thanks in advance for the quick response.

Best regards

Jeufi2000

Yes, R32 = RXVCC. Follow the stuffing table. Only one or the other is stuffed, never both together.

Please send me a picture of the following:

VIN, VOUT, VEXT nodes as power is descending.

Thank you,

Chris

Hi Jeufi2000,

It is difficult to draw a block diagram. Rather is is condition based:

1. VIN at start up MUST be greater than 4.5 V.

2. VEXT MUST be greater than 8.8 V.

3. Then VIN can descend.

4. If VEXT falls below 8 V, then switching will stop. This must stay greater than this. Then VIN can run to 2.8 V. 

Please show me a scope picture with VIN, VOUT, VEXT as VIN is descending.

Thank you,

Chris

Hello Chris,

Here is the Osci picture. that is for 12V to 4v

CH1 is Vin

CH2 is VEXT

CH3 is Vout

Thanks

BR

Tati